19/2/2015
Poor Fuel Economy
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Poor Fuel Economy Copyright AA1Car Is your vehicle delivering poor fuel economy? Have you noticed a gradual or sudden drop in the mileage you were once getting? The following are common causes of poor fuel economy that may or may not turn on your Check Engine Light or cause a loss of fuel economy: Sluggish Oxygen Sensors The oxygen sensors on your engine monitor the air/fuel mixture so the powertrain control module can add or subtract fuel as needed to meet changing operating conditions. As Oxygen sensors age, they become less responsive to changes in the air/fuel mixture, and typically produce a lean-bias signal. This tells the engine computer to add more fuel, when in fact the engine really doesn't need the extra fuel. The end result is a richer than normal fuel mixture that increases fuel consumption. The fix here is to use a scan tool and/or digital storage oscilloscope to test the response of the oxygen sensors. Or, if your vehicle has a lot of miles on it (over 100,000) to simply replace the O2 sensors if you suspect they are getting sluggish. You can also use a scan tool to look at Long Term Fuel Trim (LTFT). If the value is negative, it means the engine is running rich. This confirms the engine is wasting fuel, but it does not tell you why the engine is running rich. It could be sluggish oxygen sensors or some of the following causes. Inaccurate or Defective Coolant Sensor The coolant sensor monitors the operating temperature of the coolant that is circulating inside the engine. If the sensor is defective and reads lower than normal, or always reads cold, the engine computer will keep operating in "open" loop - which means the fuel mixture remains rich. A richer fuel mixture is required while a cold engine is warming up to prevent it from stalling. But if the mixture remains rich once the engine is warm, it wastes the extra fuel and causes poor fuel economy.
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The quickest way to check a coolant sensor is to plug in a scan tool and compare the coolant sensor reading with the inlet air temperature sensor reading when the engine is cold. But should show the same temperature reading. Then start the engine, and look for the coolant sensor to show a gradually increasing reading. If the engine eventually reaches 185 to 195 degrees ( once they warm up), the coolant sensor is probably okay. If the coolant sensor reading does not change, or never reaches normal operating temperature, the problem could be the sensor or it could be a defective thermostat that is not closing when the engine is cold. The next step would be to check the sensor's resistance reading with ah ohmmeter. If the reading does not match specifications for a given temperature, the sensor is bad and need to be replaced. If the sensor reads good, the problem is likely the engine thermostat. Defective Engine Thermostat The thermostat controls the operating temperature of the engine, and it helps the engine warm up quickly after a cold start. The thermostat is usually located in a housing where the upper radiator hose connects to the engine. When the engine is cold, the thermostat closes to block the flow of coolant. When a cold engine is started, the thermostat should remain closed until the coolant gets hot (around 185 to 195 degrees). If the thermostat does not close tightly or does not close at all, coolant will be circulating while the engine is trying to warm up. This will prevent the engine from warming up quickly, and it may never reach normal operating temperature. This can delay the powertrain control module from going into closed loop operation, causing a rich fuel mixture and poor fuel economy. A quick check for this problem is to feel the upper radiator hose while the engine is warming up. If you feel coolant circulating through the hose following a cold start, the thermostat is probably stuck open. The fix is to replace the thermostat. Engine Misfire If an engine is misfiring for any reason, it will waste a LOT of fuel and result in poor fuel economy. Misfires can be caused by ignition problems such as worn or fouled spark plugs, bad plug wires, weak ignition coils or arcing between the plug wires or coil and ground. Misfires can also be caused by dirty or defective fuel injectors, vacuum leaks in the intake manifold, or low fuel pressure. Misfires can also be caused by loss of compression in one or more cylinders. On 1996 and newer vehicles with OBD II, misfires should turn on the Check Engine Light and set a misfire code if the misfires are severe enough to cause an emissions problem. However, if the misfire rate is just below the threshold where a code must be set, you won't get a code or Check Engine light. If you have access to a factory scan tool or a professional level scan tool that can read something called "Mode $06" data, you can look at the actual misfire rates for each of the cylinders. from this, you can see if one or more cylinders are misfiring (even if they have not yet set a code). If you do have a Check Engine Light and a cylinder specific misfire code (such as P0301 which would indicate cylinder #1 is misfiring), inspect the spark plug, plug wire (if used) and coil for that cylinder. If the ignition components appear to be working normally (no fouling, no shorting or arcing), the problem is likely a dirty or dead fuel injector. If you get a P0300 "random misfire" code, the most likely cause is a lean fuel mixture due to an intake manifold vacuum leak, leaky EGR valve, or low fuel pressure. Intake Manifold or EGR Valve Leak A vacuum leak at the intake manifold gasket, in the manifold itself or any of its vacuum hose connections can lean out the air/fuel mixture and cause the engine to misfire and deliver poor fuel economy. Likewise, an EGR valve that does not close at idle, when the engine is cold or when it is not under load can allow exhaust to leak back into the intake manifold. This can also have a leaning effect and cause fuel-wasting misfires and poor fuel economy. You need to check for vacuum leaks, and/or remove and clean the bottom of the EGR valve. Vacuum leaks can be found by spraying throttle cleaner along the edges of the intake manifold while the engine is idling. If the idle suddenly dhanges, it means some of the cleaner is being pulled into the engine through a leak. The fix usually requires replacing the intake manifold gasket, or the manifold itself if it is cracked. A cheaper fix is to apply a high temperature epoxy sealer to the crack and hope it seals the leak. NOTE: It does not take much of a leak to upset the air/fuel ratio. Even a very small leak can cause problems. Professional technicians often use a device called a "smoke machine" to find small leaks. The machine generates a mineral vapor smoke, which is fed into the manifold (engine off). If there are any leaks, you will see the smoke seeping through the crack.
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If no vacuum leaks are found, remove the EGR valve and check the underside of the valve and the port in the intake manifold for carbon deposits that may be preventing the valve from closing. Also, check the EGR valve's vacuum connections and solenoid to see if they are operating properly. There should be NO vacuum reaching the valve at idle or when the engine is cold. Worn or Fouled Spark Plugs Worn or fouled spark plugs will obviously cause fuel-wasting engine misfires. Platinum and Iridium plugs should last 100,000 miles, but short trip stop-and-go driving may cause the plugs to foul prematurely. An engine that is using oil can also foul out its spark plugs. Remove and inspect the spark plugs. Clean the plugs if they are dirty, and regap to specifications, or better yet, just install a new set of spark plugs. Dirty Fuel Injectors Fuel varnish deposits can build up inside fuel injectors, preventing them from delivering their normal dose of fuel. This can cause a lean air/fuel mixture that results in lean misfires and wasted fuel. Try adding a bottle of good quality (not the cheapest stuff) fuel injection cleaner to your fuel tank. It may take several tankfulls before any improvement is noticed. If that does not work, having the injectors professionally cleaned will often restore normal performance. If an injector is too badly clogged to be cleaned, or it is defective, you're looking at replacing one or more fuel injectors (which aren't cheap to replace!). Low Compression If you are driving a high mileage vehicle (over 100,000 miles), you may be getting poor fuel economy because your engine does not have the compression it once had. As the miles add up, so does the wear on the piston rings and valves. This can result in a gradual loss of compression that reduces engine efficiency and fuel economy. If you suspect low compression, do a compression test on the engine. If low, there is no easy fix other than an overhaul. There's no miracle cure in a can that will restore lost compression. Wrong Oil Viscosity Most late model passenger car engines today require a low viscosity 5W-20 or 5W-30 motor oil. Some even specify 0W-20. Such oils improve fuel economy, especially during cold weather when the oil tends to thicken. If you are using a heavier viscosity motor oil, it can reduce your fuel economy (maybe 5 to 10 percent depending on what you are using). Dirty Air Filter If your air filter is really dirty, it will interfere with normal engine breathing and hurt fuel economy. Remove and inspect the filter, and if it is dirty replace it with a new one. Clogged Converter or Exhaust Restriction Any obstructions in the exhaust system will create power-robbing backpressure that also hurts fuel economy. You can inspect the outside of the system for any obvious signs of damage such as a crushed or crimped pipe. But internal problems such as a clogged converter or collapsed muffler or double walled pipe can't be seen from the outside. You can check for an exhaust restriction by connecting a vacuum gauge to the intake manifold. At idle, the engine should show a high and steady vacuum reading (say 18 inches or higher). If the reading is less than this or it gradually drops, you have an exhaust restriction. Slipping Clutch or Transmission If the clutch on a manual transmission is slipping, or the bands or torque converter lockup on an automatic transmission are slipping, some of the engine's power will be lost before it can reach the wheels. This can cause a noticeable drop in fuel economy -- and be VERY expensive to fix because it will require replacing the clutch or transmission.
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Low Tires To achieve maximum fuel economy, your tires must be inflated to the recommended pressure for your vehicle and load. For most passenger car tires, that means 32 to 34 PSI. A low tire increases rolling resistance (and tire wear), and can result in a loss of 5 to 10 percent fuel economy. Check all four tires (when cold) with an accurate gauge, and inflate as needed to the recommended pressure. Dragging Brakes A parking brake that is not fully releasing, or a brake caliper that is sticking can cause the brakes to drag and your engine to waste fuel. A quick check for this kind of problem is to park your vehicle on a slight incline, put the transmission in neutral, then release the brake pedal. If your car does not start to roll immediately, the brakes may be dragging. Too Much Junk in Your Trunk More weight equals less fuel economy. It takes power to move mass, so if you are hauling a lot of unnecessary weight in the trunk or cargo area of your vehicle, you are not going to achieve maximum fuel economy. Poor Driving Habits This is probably the most common problem and biggest fuel waster of all. Aggressive driving and jack rabbit starts flood the engine with extra fuel. Take it easy, as if you were driving with a raw egg under the gas pedal and you'll get the most miles per gallon from the fuel in your tank.
For Fuel Saving Tips from the Car Care Council, Click Here.
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More Fuel System Related Articles: Fuel Saving Tips from the Car Care Council Gas Saving Gadgets Most Fuel Efficient Cars for 2011 Most Fuel Efficient Cars for 2009 Most Fuel Efficient Cars for 2008 Troubleshooting Engine Misfires Troubleshooting & Cleaning Fuel Injectors Compression Testing Spark Plugs (Why They Need To Be Replaced)
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Car Won't Start
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Car Won't Start? Copyright AA1Car YOU TRY TO START YOUR CAR BUT IT WON'T START What should you do when your car won't start? Diagnosing a no-start condition requires a logical approach to figuring out what might be preventing your car from starting. Below is a list of possible causes that can prevent your car from starting.
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... When you turn the ignition key to start your car, or press the START button, voltage from the battery flows through the ignition switch to the Park/Neutral safety switch and/or brake pedal or clutch pedal safety switch (you have to push the pedal down before the circuit will complete) to the starter relay or solenoid. When the relay or solenoid is energized by voltage from the ignition switch circuit, it closes a contact that routes more power from the battery directly to the starter to crank the engine. The starter motor spins, pushes the starter drive gear to engage the flywheel and cranks the engine. If the engine fails to crank, there is a fault in one of the components in the battery/ignition/starter circuit.
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COMMON CAUSES OF NO-CRANK NO-START Low battery (Check battery voltage, recharge if low, or jump start with another vehicle or battery charger). Loose or corroded battery cables (Inspect, clean and tighten BOTH ends of BOTH battery cables). Bad starter relay wiring connections or ground connection (Inspect, clean, tighten wiring connections). Bad starter relay/solenoid (Check for voltage at relay, if relay has voltage but there is no "click" when key is turned to start, replace relay). Bad starter (Jump battery voltage direct to starter to see if it spins, or remove starter and have it bench tested at auto parts store). Damaged starter drive or teeth on flywheel (Remove starter and inspect drive gear and flywheel teeth, replace damaged parts if necessary). Bad ignition switch (Check to see if voltage reaches starter relay/solenoid when turn to start. If not, check for open P/N switch and brake or clutch pedal switch. Replace ignition switch if defective). Open P/N safety switch, or open Brake Pedal Safety Switch (automatic transmission) or open Clutch Pedal Switch (manual transmission). Bypass switch with jumper wire to see if engine cranks, or use test light or voltmeter to check for voltage passing through switch when ignition is turned to start. Engine seized due to bearing failure or internal damage (Use socket and long handle to see if engine can be turned by hand, if not engine is locked up). Engine hydrolocked due to coolant leak from leaky head gasket (Use socket and wrench to see if engine rotates, remove spark plugs and see if coolant comes out or engine can not be cranked with plugs out).
ENGINE CRANKS OKAY BUT WON'T START If the engine cranks over normally when you attempt to start you car, but the engine does not start, the problem may be NO FUEL, NO SPARK or NO COMPRESSION. The engine needs adequate fuel pressure, a properly timed spark and normal compression to start. TIP: To find why the engine won't start, remove the air inlet tube from the throttle body, push the throttle open and spray a small amount of aerosol starting fluid into the engine. Crank the engine. IF it has spark and compression but NO FUEL, it will start and run a few seconds before dying. If it does NOT start, it probably has NO SPARK. TIP: Another method to check for spark is to pull a spark plug wire off of a spark plug (if it has plug wires, coil-on-plug ignitions do not) and place the open end of the plug wire near a metal surface on the engine. Have a helper crank the engine while you watch for a spark. DO NOT hold the wire while doing this as it can shock you. If you see a spark, the problem is not spark, but most likely NO FUEL or NO COMPRESSION. If you do not see a spark, the problem is in the IGNITION CIRCUIT. TIP: Proper fuel pressure is critical for fuel injected engines to start and run. You should hear the fuel pump inside the fuel tank buzz for a couple of seconds when the ignition is turned on (no buzz means the pump is not running and the engine is not getting fuel). You can smell the tailpipe for gasoline vapors after cranking the engine. If you smell gas, the problem is likely not fuel but NO SPARK. You can also remove the plastic cap and press the schraeder valve test fitting on the fuel rail to see if there is any fuel pressure to the engine (not a very accurate test because fuel pressure must be at a certain level for the engine to start, for that you need a gauge). Even so, no fuel at the fuel rail would tell you fuel is not getting to the engine.
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Car Won't Start
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FUEL RELATED CAUSES OF A NO START If your Anti-Theft light is flashing, the anti-theft system is disabling the fuel pump to prevent the engine from starting. The problem could be a defective chip in a smart key, or a dead battery in a smart key or keyless entry fob, or a fault in the AntiTheft system itself. See Diagnose Anti-Theft System for help. Bad fuel pump (Pump should run for a few seconds when ignition key is turned to start, no buzz means no fuel delivery to the engine). Bad fuel pump relay (Relay is energized by PCM to route power to fuel pump when ignition is on). Bad inertia fuel shut-off safety switch (Shuts off fuel in an accident, may have been tripped by a severe jolt, press button to reset). Open in wiring anywhere in fuel pump wiring circuit (power or ground). Problem may be at wiring connector on top of fuel tank (hard to reach!). No gas in fuel tank (Check the fuel gauge, and keep in mind the gauge may not be reading accurately). Bad gas (Contaminated with water or too much alcohol or diesel fuel). If you just filled up with gas and now your car won't start, suspect bad gas. Plugged Fuel Filter (When was the filter last changed?). Replace the filter. If plugged with rust,k fuel tank may also need to be cleaned or replaced. Plugged or Pinched Fuel Line (Inspect fuel lines under vehicle for damage). Leaky Fuel Pressure Regulator (Controls fuel pressure to injectors, which is critical for starting and proper air/fuel mixture). No power to Fuel Injectors (Due to faulty fuel injector relay, blown fuse, no input signal to PCM from crank position sensor or cam position sensor, or bad PCM driver circuit). Injectors should usually have power when key is on. PCM grounds other side of injector circuit to pulse the injectors. Major vacuum leak (An open EGR valve, disconnected vacuum hose, PCV valve, etc, can create a large vacuum leak and allow too much air to be sucked into the engine. This will make the air/fuel mixture too lean and make the engine hard to start. Engine will usually idle rough if it does start.
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Car Won't Start
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IGNITION RELATED CAUSES OF A NO START Bad crankshaft position sensor or distributor pickup (Sends pulse signal to ignition module and/or PCM that is necessary to trigger the ignition coil(s)). Bad ignition module (controls firing of ignition coil(s), may have an intermittent open in circuitry that causes loss of spark, hard starting or sudden stalling, usually when hot) Bad ignition coil(s). Ignition coil creates high voltage to fire the spark plugs. On engines with a distributor, a bad coil will prevent spark at all the spark plugs. On engines with a distributorless ignition system or coil-on-plug ignition, a bad coil will only affect one or two cylinders depending on the application. This may make the engine hard to start, but it will run on the remaining cylinders that are firing. Cracks or carbon tracks inside distributor cap or on rotor (allows spark to short to ground before it reaches the spark plugs). Bad spark plug wires (if wet, cracked, burned or internal resistance exceeds specifications, can interfere with good spark and make engine hard to start). Fouled spark plugs (if the electrodes are contaminated with deposits, spark may short to ground before jumping gap causing misfires. Can make engine hard to start and run poorly. If plugs are wet when removed, it means they are not firing or engine is flooded).
COMMON CAUSES OF NO COMPRESSION Broken timing belt or chain (Belt failure will prevent the valves from opening. The engine will NOT run if the belt has broken, and it may have bent valves or other damage as a result of the belt breaking). Broken camshaft (This can happen on an overhead cam engine if the engine has overheated, warped the head and seized the camshaft). Plugged catalytic converter (Creates a restriction that causes exhaust backpressure to back up. Engine may start but usually dies within a minute or two).
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Diagnose Anti-Theft System
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Diagnose Anti-Theft System Copyright AA1Car
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. Anti-theft systems are designed to deter auto theft. Most do a pretty good job of doing just that. But anti-theft systems also cause a lot of annoying problems when they act up. Your car might not start. Or, the system may suddenly kill the ignition while you are driving, causing your car to stall. Or, the alarm may go off when you open the door with the key and not shut off. Or the alarm may go off for no apparent reason. Factory installed anti-theft systems are usually more reliable and less apt to misbehave than aftermarket anti-theft systems. One of the reasons for this is how the system in installed in the vehicle. The factory systems are usually integrated into the body control module (BCM) and powertrain control module (PCM), and are designed to prevent the vehicle from starting if someone attempts to start the engine without the key. Many factory systems will also sound an audible alarm (the horn or a second hidden horn) and flash the lights if someone opens a door without first unlocking it with the key or keyless entry fob. Most aftermarket systems are designed to do the same thing, but may also include a remote starting capability, GPS tracing if a vehicle has been stolen, and even remote disabling. The main problem with aftermarket installations is the installer. If the person who wires the anti-theft system into the vehicle is properly trained and does a professional job, you shouldn't have any issues with the system as long as it is working properly. But if the installer does a hack job of splicing into the wiring, he may create a variety of potential problems. Tapping into the wrong power circuit may rob voltage from a critical system, causing other problems that may seem to be unrelated to the anti-theft system. We've heard of aftermarket anti-theft systems setting engine misfire codes because it was cutting out the ignition for a split-second or two while the vehicle was being driven. Another issue with some aftermarket anti-theft systems is the quality or durability of the electronics used in the anti-theft module. A lot of electronics come from China these days, and a lot of this stuff uses recycled chips and other components, or ones that are very poor quality. Consequently, a year or two down the road, the electronics crap out and the system starts to cause problems or fails completely. The only fix for this is to buy a system that has the longest possible warranty, and hope the manufacturer is still in business and will honor that warranty should you have an issue later on.
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Diagnose Anti-Theft System
Diagnosing an Anti-Theft System Problem If the security or anti-theft light is flashing when you attempt to start your car, and the engine does not crank or does not start, you have an anti-theft problem. The system may not be recognizing your key or keyless entry signal, or there may be a fault in the anti-theft module, keyless entry system or wiring. If your vehicle has a smart key or smart key fob, the battery in the key or fob may be dead, or there may be a fault in the key or fob chip that is preventing the Anti-Theft system from recognizing it. A dealer will have to diagnose the system with a factory scan tool to determine what might be causing the problem.
Can You Disable or Circumvent Your Anti-Theft System? If it is a factory-installed system, probably not. Remember, these systems are designed to thwart auto theft, so if they could be easily disabled or bypassed, auto thieves would do so. There are always ways to get around an anti-theft system, but most are too time-consuming or expensive or complicated for the average do-it-yourselfer to attempt. Besides, if we told you the secrets of how to bypass your anti-theft system in this article, we'd be giving the keys to your car to anybody who might want to steal it. If the anti-theft system is an aftermarket system, and you have the installation manual or instructions that came with it, you could find all the places where it is spliced into the wiring and disconnect the system. Or, you could take it back to the installer and ask them to remove it or replace it with a new system.
Only Car Dealers or Certified Repair Outlets Can Access the Anti-Theft System One of the protective measures that is designed into today's anti-theft systems is that only new car dealer personnel with factory scan tools can access the system for diagnosis or repair. So if you have a problem with a factory-installed anti-theft system, it will most likely mean a trip to the dealer for diagnosis and repair. NOTE: Certified locksmiths who have undergone screening, are bonded and have met all the criteria for anti-theft access can also qualify for gaining access to anti-theft service information. But because of the cost involved, not many have signed up for this program.
Factory Anti-Theft Systems Various types of anti-theft systems are used by vehicle manufacturers: General Motors has one system called a Content Theft Deterrent (CTD) system that sounds an alarm if the doors are opened without the key. But the system does not prevent a car thief from driving your car away. Factory anti-theft systems that disable the ignition, the fuel system or the starter to prevent your vehicle from being stolen include GM's Vehicle Theft Deterrent (VTD) or Passlock system, Ford's Passive Anti-Theft System (PATS), and Chrysler's Sentry Key Immobilizer System (SKIS). Most use an ignition key that contains a coded transponder chip. The key is read by a transponder receiver in the ignition switch. The key signal is then routed through the anti-theft module or body control module (BCM) to the engine computer, which receives either a "go" or no go" signal. If the PCM receives a no-go signal or no signal at all from the anti-theft system, the computer won't enable the ignition, fuel system or starter (depending on how it is configured) so the engine won't start when you turn the key. Here's a related article on how to fix a Chevy Malibu that won't start or stalls because the Anti-Theft System has codes DTC P1626, P1630 or P1631. Your main clue as to whether or not you are dealing with an anti-theft system problem or some other type of problem (see Engine Won't Start article) is the security or anti-theft light. If the light continues to flash when you attempt to start the engine, the anti-theft system is sending out a no-go signal and you are not going anywhere. Call a tow truck and have your car towed to the dealer for diagnosis and repair.
What Goes Wrong with Anti-Theft Systems The anti-theft system may not be recognizing your key because the chip inside the key is faulty or has been damaged. Or it may not be reading the key because of a fault in the receiver inside the ignition switch. Sometimes interference from other computer chip keys on your key ring may be interfering with the signal that the correct key is supposed to be sending to the receiver in the ignition switch. http://www.aa1car.com/library/troubleshoot_antitheft_system.htm
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Chrysler had a problem with this on some of their cars if the vehicle owner had a second key to a different Chrysler on the same key ring. Sometimes the anti-theft receiver would read the correct key and start. The next time, it might read the wrong key (even though the other key was not in the ignition) and not start. Or worse yet, it might lose the signal from the correct key while driving and pickup up the other key, causing the engine to suddenly stall. The fix was to tell motorists with this problem NOT to put two different Chrysler keys on the same key ring. If your car has a keyless entry system or remote starter, and is not starting (anti-theft light flashing), the battery inside your keyless entry fob may be dead (try changing the battery), there may be a fault in the fob itself (try a second fob for your car if you have one), or the receiver may not be picking up the signal. The only fix for the latter is to have the dealer see if the module is receiving a signal and processing it correctly. If it is not, they will have to replace the keyless entry receiver or antitheft module.
Anti-Theft System Reprogramming If you have a bad key, have lost your keys, or the anti-theft module has been replaced, the anti-theft system will have to be reprogrammed to identify and accept the new keys or replacement module. On some Mercedes models, the ignition keys are matched to the PCM. This means you have to also have to replace the PCM if you lose your keys because reprogramming is not possible! Reprogramming can only be done by a dealership technician using a factory scan tool, or by an authorized locksmith if you can find one who can do computer keys. The typical charge for this may be $75 to $150 depending upon how long the procedure takes. Some anti-theft system reprogramming or relearning procedures can take 20 to 30 minutes or more to complete. Time-delays are built into the procedure to discourage someone from using a factory scan tool and access codes from hacking your car's anti-theft system and reprogramming the keys. Got an Anti-Theft System Problem? Need Help Now? Click the Banner Below to Ask an Expert:
News Flash:
Your Keyless Entry System May be Vulnerable to Hacking! Think your keyless entry system can't be hacked? Think again. Car thieves have come up with a clever way to fool remote keyfobs into sending out a signal to unlock the doors on your vehicle and possibly start the engine. A keyless entry fob will broadcast its radio signal when it is within about 25 feet or so of your vehicle. To hack the signal, a would-be car thief places a small fake antenna near you that fools your fob into thinking you are approaching your vehicle. When the fake antenna receives the coded signal from your fob (which you never knew it sent), the signal is resent to a second antenna placed near your vehicle to unlock the doors and enable the ignition. But the engine will only start if your vehicle has a push button starter. This trick may allow a thief to enter your vehicle, but they won't be able to start the engine if your vehicle has a conventional key lock ignition on the steering column.
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Diagnose Ignition Switch Problems
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Diagnose Ignition Switch Problems Copyright AA1Car The ignition switch is the master switch that provides power for the vehicle's electrical accessories, computer, fuel and ignition systems. It also routes current from the battery to the starter to crank the engine. An ignition switch has four positions: OFF - Or LOCK position, Turns off power to the engine and electrical accessories ACC - Accessory position that provides power to electrical accessories only, not the engine. RUN - The "ON" position that provides power to the engine and electrical accessories. The switch must be in this position for the engine to run and for the vehicle to be driven. START - Used only to start the engine.
IGNITION SWITCH ANTI-THEFT FUNCTIONS The ignition switch also serves as a theft prevention device. A key is required to turn the switch. The key portion of the switch (which is often a separate component from the multi-contact electrical part of the switch) works like any other lock. Inserting a key into the switch moves a row of pins inside a cylinder. If the pins line up correctly, the cylinder will turn allowing the switch to change position. If the pins don't line up, they prevent the switch from turning. Problems here can be caused by a worn key and/or worn pins inside the cylinder. On applications where the electrical part of the switch is a separate component behind the key cylinder, removing the key cylinder allows the switch to be turned manually (typically with a large screwdriver). On older vehicles, car thieves would use a slide hammer or pry bar to pop the key cylinder out of the ignition switch so they could start the engine without a key. But all that changed when auto makers began using anti-theft systems that included a coded "computer" key.
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Diagnose Ignition Switch Problems
On newer cars, the engine won't start even if the key cylinder has been removed because the computer must receive the proper code from the key. If the vehicle has a push button start system (no key), the anti-theft code comes from the key fob. If there's no code (or the wrong code), the computer won't energize the fuel pump or start the engine -- and the thief can't steal the car. Starting problems here can occur if the circuit that reads the smart key or key fob is faulty and doesn't recognize or transmit the proper signal back to the computer. The same thing can happen if the smart key or key fob is defective or damaged. On some applications, the anti-theft system can be confused if there are more than one smart key on the key ring and the system is reading the wrong key. This may happen is the second or third keys are for a similar make/model of vehicle rather than a different make/model of vehicle.
IGNITION SWITCH INTERLOCKS The ignition switch is also used to lock the steering wheel when the key is removed. This is also to reduce auto theft. On vehicles with automatic transmissions, there is also a "shift interlock" solenoid that locks the transmission linkage so the transmission cannot be shifted out of Park. Problems with the column lock (such as binding) may prevent the ignition switch from turning when the key is inserted, or it may prevent the key from being removed when you turn the engine off. Problems with the shift interlock solenoid may prevent the transmission from being shifted out of Park. The cause may be a bad solenoid, an electrical fault between the ignition switch circuit and the interlock solenoid, or binding in the shift interlock linkage.
COMMON IGNITION SWITCH PROBLEMS Common problems with ignition switches include any of the following:
IGNITION SWITCH WON'T TURN WHEN KEY HAS BEEN INSERTED Try jiggling the steering wheel back and forth. The steering column may be binding because one of the front wheels is turned at an angle against a curb. This puts a load on the steering linkage, which may be enough to bind the column lock and ignition switch. A worn key (or the wrong key) can prevent the ignition switch from turning. If you have a spare key, try the spare key in the ignition switch to see if it works. If the spare key works, the problem is not a bad ignition switch but a bad key. Throw the old key away and get a new copy made of the spare key. If you have no spare key, a lock smith may be able to make you a new key using a key code from the owner's manual or auto maker. If that is not an option, the key cylinder in the ignition switch will have to be replaced along with a new set of keys. If the ignition switch is binding (hard to turn in either direction), lubricating the switch may help. Use a nonconductive lubricant such as dielectric silicon grease or aerosol electronics cleaner. CAUTION: Do not use penetrating oil or graphite because it might short out the electrical contacts inside the switch.
IGNITION SWITCH TURNS ON BUT ENGINE WILL NOT CRANK If nothing happens when you turn the ignition switch to the start position, the problem may be a bad ignition switch, or it may be a fault in the starting circuit.
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First, do the instrument panel warning lights come on when the key is turned to the ON position? No warning lights or other signs of electrical activity could indicate a dead battery or that the battery cables are loose or corroded. Try turning on the headlights. No lights? Then you have a battery or battery connection problem. If the headlights work, the problem is not the battery but an electrical fault in the ignition switch, ignition switch circuit (wiring or fuse), or a problem in the starting circuit (bad relay, solenoid, wiring or starter).
IGNITION SWITCH TURNS ON AND ENGINE CRANKS BUT WILL NOT START
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The problem here is probably an anti-theft fault, or a fault in the fuel pump circuit, ignition circuit or engine computer. If the anti-theft light is flashing, the computer is NOT recognizing the key or key fob and is preventing the engine from starting. This could be due to a bad receiver in the ignition switch that reads the key, a damaged smart key or key fob, or a wiring fault between the switch and computer. On some vehicles, reprogramming the computer may be required so the computer will correctly recognize the smart key or key fob. You can't circumvent an anti-theft system because it is hard wired into the computer.
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If the anti-theft light is NOT flashing when you attempt to start the engine, and the engine is cranking normally, the computer is recognizing the key but the engine may not be starting because it is Learn More not getting fuel or spark. Check the fuel gauge to make sure it is not on empty. Got fuel? Listen for the fuel pump to buzz when the key is first turned on. No buzz means a fault in the fuel pump, pump relay or pump wiring. There could also be a problem in the ignition system (such as a bad crankshaft position sensor, ignition control module or computer) that is preventing the engine from starting. See the related articles on these subjects for further diagnosis. If the engine cranks, but much slower than normal, the problem is not a bad ignition switch but low voltage to the starter (check the battery and cable connections) or a bad starter.
ENGINE STARTS AND RUNS NORMALLY, BUT SUDDENLY DIES WHILE DRIVING This is one of the most common symptoms of a worn ignition switch. Worn contacts inside the switch may cause a momentarily loss of voltage as a result of heat or vibration (as when driving on a rough road or hitting a bump). Any loss of power through the ignition switch will cause the engine to stumble, misfire or die. Ignition switches wear from normal use. The more you drive your vehicle, the more times you use the ignition switch. After many years and miles, the electrical contacts inside the switch may become worn or corroded, resulting in poor or intermittent electrical contact. The wear problem can be made worse by heavy key rings that place extra stress on the switch. A large heavy key ring that rocks and sways as you drive twists and tugs on the switch. Over time, this will accelerate wear and eventually cause the ignition switch to fail.
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ADVICE: Lighten your key ring as much as possible. Don't carry extra keys, fobs, remotes, pendants, jewelry or other things on the key ring that you don't really need.
KEY WON'T COME OUT OF THE SWITCH WHEN YOU TURN THE ENGINE OFF his may be due to binding in the steering column lock. Try jiggling the steering wheel back and forth until you feel it "click" into a locked position. You should now be able to remove the key from the switch. If the key still won't come out, the problem may a damaged column locking mechanism, or one or more pins sticking inside the key lock cylinder.
KEY IS BROKEN OFF INSIDE THE IGNITION SWITCH Your best option here is to find a lock smith and have them try to remove the broken key from the ignition switch. If the broken key can be successfully removed, you can use a spark key (if you have one) or get a new key made from the old broken key (which may or may not be possible depending on the damage). If a new key cannot be made from the broken key and you do not have a spare key, you will have to get a new lock cylinder and keys. If your vehicle has a smart key, the new key will have to be programmed to the computer. This usually requires having your vehicle towed to a new car dealer or other authorized repair facility so the computer can be programmed to recognize the new key.
REPLACING AN IGNITION SWITCH The easiest and safest way to replace an ignition switch is to take your vehicle to a repair shop or new car dealer and have them replace your ignition switch. Ignition switches are often difficult to replace by design. Auto makers make the switches hard to remove to deter auto theft. Ignition switches that are mounted on the steering column are usually located under some type of shroud or trim cover that must first be removed to access the switch. NOTE: On some applications, the switch must be in a certain position before it is removed or installed so that it will align properly. Always refer to a service manual for removal/installation instructions BEFORE you attempt to replace the switch. Also, on newer vehicles with smart key anti-theft systems, a special "learn procedure" or reprogramming the computer is usually required after the ignition switch has been replaced. If this is not done, the engine won't start and run. WARNING: On airbag equipped vehicles, the air bag system should always be deactivated before you attempt to replace the http://www.aa1car.com/library/ignition_switch.htm
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ignition switch to prevent the accidental deployment of the driver's airbag. The airbag can be deactivated by removing its power fuse, or by disconnecting the battery. Wait at least 15 minutes after deactivating the airbag system to start work so the capacitors that store reserve power for the airbags have time to discharge. On some vehicles with a column-mounted ignition switch, it may be necessary to remove the steering wheel to replace the ignition switch. This requires deactivating the airbag system and using a steering wheel puller to remove the steering wheel. CAUTION: Care must be taken to make sure the steering wheel is removed and installed properly so the airbag connections are not damaged, and are reconnected correctly so the airbag will work.
IGNITION SWITCH RECALLS In some cases, auto makers have issued safety recalls for vehicles with known ignition switch problems. Other times, they have issued technical service bulletins that describe ignition switch faults and recommended repairs. Recalls typically involve inspecting and/or replacing the original switch with a redesigned switch at no cost to the vehicle owner. Safety recalls with free repairs are generally good for a fixed period of time/mileage from the date of manufacture. TSBs, on the other hand, do NOT cover free repairs, and only offer suggested repairs for a specific problem or symptom. Some notable recent ignition switch recalls include:
June 16, 2014 - GM Recalls Another 3.3 Million Cars for Ignition Switch Risk General Motors has recalled 3.3 million of its vehicles for a problem that could allow the ignition switch to turn itself off. The problem is the key. The key has a slot across the top so the key can be attached to a key ring or fob. The problem is the slot allows the key ring or fob to slide and tug on the key. If there is a lot of weight on the key ring and the vehicle hits a bump or rough stretch of road, it's possible for the key to jiggle out of the RUN position and turn the ignition off. If this happens, the vehicle loses power steering and brake assist, and the airbags are turned off (which means they can't deploy if the vehicle hits something). The latest recall affects the following 2000 to 2014 model year GM cars: Buick Lacrosse, 2005-2009 Chevrolet Impala, 2006-2014 Cadillac Deville, 2000-2005 Cadillac DTS, 2004-2011 Buick Lucerne, 2006-2011 Buick Regal LS & GS, 2004-2005 Chevy Monte Carlo, 2006-2008 The fix is to replace the original ignition key that has a slotted head with one that has only a single small hole for a key ring. This will keep the weight on the key ring from twisting the key out of the RUN position. You can also fix the problem yourself by removing the key from your key ring or fob and using the key by itself.
June 13, 2104 - GM Recalls Half a Million Camaros over Ignition Switch Issue GM issued a safety recall notice for over half a million 2010 to 2014 Camaros because of the design of the ignition switch key fob. The key is part of the fob, and the fob protrudes in such a way that the driver may accidentally bump the key fob with his or her knee while driving, causing the switch to flip from the ON position to ACC or OFF. This causes the engine to quit running as well as a loss of power steering and brakes. Also, the air bags are deactivated when the ignition is not in the ON position (which means no air bags if you crash!). The car will still steer and brake with the key not in the ON position, but both require increased effort from the driver. The fix is to replace the original key fob with one that has a separate key and fob.
February 2014 - GM recalls 1.6 million vehicles for faulty ignition switch. The ignition switch recall affects 2005 to 2007 Chevy Cobalt and Pontiac G5, 2006 to 2007 Chevy HHR and Pontiac Solstice, and 2003 to 2007 Saturn Ion and 2007 Saturn Sky. The ignition switches on these vehicles may fail or rotate to the Accessory or OFF position as a result of vibration or wear (a problem GM has blamed on heavy key rings). The ignition switch problem may cause the engine to suddenly stall while http://www.aa1car.com/library/ignition_switch.htm
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driving. The loss of power also causes a loss of power steering assist (which increases steering effort), and cuts power to the airbags (which prevents the airbags from deploying if the vehicle is involved in an accident at the same time). GM says it will replace the ignition switches in the recalled vehicles at no cost to the vehicle owner.
This is the troublesome ignition switch that led to the GM safety recall.
June 2012 - GM Recalls Various Chevy Cobalt & HHR, and Pontiac G5 Models for Sticky Ignition Switch Recall bulletin 12089A issues June 6, 2012 recalled 2007 to 2008 Chevy Cobalt, 2008 to 2009 Chevy HHR and 2007 to 2008 Pontiac G5 models for a sticky ignition switch that may make it difficult of impossible to turn the switch and/or remove the key. The recall covers the above vehicles for 10 years or 120,000 miles from date of manufacture. The replacement ignition switch cylinder kit for these vehicle is P/N 20869121.
Ford Recalls 8 Million Vehicles for Ignition Switch Fire Hazard Starting in 1996, Ford issued a series of recalls for various 1988 through 1993 models for faulty ignition switches that could short out and start a fire. Similar recalls were issued later for various 1992 through 2003 models for the same problem (as well as a faulty cruise control switch that could short and catch fire). The ignition switches recalled were found to have badly worn brass contacts that could short out and start a fire even if the vehicle was parked with the ignition OFF.
Related Articles: Troubleshoot an Engine That Won't Crank Troubleshooting a Car That Won't Start http://www.aa1car.com/library/ignition_switch.htm
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Diagnose Intermittent Engine Problems
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Diagnose Intermittent Engine Problems Copyright AA1Car.com Adapted from an article written by Larry Carley for Underhood Service magazine An intermittent engine problem can be a nightmare to diagnose. Problems that come and go or only occur under certain driving or operating conditions can be very difficult to troubleshoot, unless you have a diagnostic strategy to outwit these kinds of problems. One thing all intermittent problems share in common is they are not a steady-state condition. If an engine dies and refuses to start, you can check for spark, fuel and compression to start isolating the cause. But when you have an engine that runs fine one minute, then dies, bucks, hesitates or misfires, then runs fine again, it is a different story. Something is obviously occurring that is interfering with normal combustion. But what? Is it the ignition system, fuel system, computer or something else? That is where a diagnostic strategy comes in. The worst kind of intermittents are those that occur infrequently, say once a week or less. Your odds of correctly diagnosing an infrequent intermittent are probably the same as winning the lottery. Unless you are lucky enough to catch the problem when it is occurring, you will have few clues to go on. You can always guess at a diagnosis based on a hunch or previous experience, but the odds of hitting the target every time are pretty slim. That is how parts changers "fix" cars. They replace the part they think might be causing the problem, and when that fails to cure the problem they replace something else and so on. Eventually they may replace the right part that was really causing the problem. But in the meantime, they have bought a lot of parts they didn't really need. Engine Diagnostic Strategies There are better ways to tackle intermittent engine problems. One is to wait until the intermittent has become a more frequent or continuous problem. It's always easier to diagnose a part that has failed than one which is only misbehaving. But if you can't depend on your car and don't want to get stranded, you need to fix it now. One time-saving step that may allow you to zero right in on the cause is to check for any technical service bulletins that might be out on the problem. It may be a situation where there is a pattern failure and the vehicle manufacturer has already done the diagnostic homework and figured out the solution for you. In many cases, taking a few minutes to
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check for a possible TSB can save you hours of frustration and wasted diagnostic time. The cure may not be to replace a part but to reflash the computer to change its operating instructions. The next thing you should always do is hook up a scan tool and check for trouble codes even if the Malfunction Indicator Lamp (MIL) is not on (the lamp may be defective). Depending on the system and scan tool you use, you also should take a look at any history codes or pending codes that may be in the Powertrain Control Module (PCM) memory. Also, look at some of the data stream perimeters like long- and shortterm fuel trim, oxygen sensor cross counts, TPS and MAP sensor signals. See anything that looks out of range? It might be a clue as to what’s causing the problem.
Another basic check that should always be made is the battery voltage and charging voltage. A low battery, weak alternator or overvoltage condition can all play havoc with onboard electronics. Solenoids and relays all require minimum voltages to function properly, so if the battery or charging system is not within normal specifications, you may have found the root of the problem. If a problem has left no tracks (no trouble codes or odd readings to steer you in a particular direction), your next task is to establish a pattern - if there is one. Does the problem only seem to occur during certain operating conditions? The two most common types of intermittent problems are an engine that cranks but may not start under certain conditions, and an engine that runs fine but occasionally experiences some kind of driveability problem such as stalling, surging, hesitation, stumbling, bucking, misfiring, knocking, rough idle, idles too fast, etc. In both cases, the intermittent may only occur during some kind of environmental or operating condition (only during wet or rainy weather, only when hot, only when cold, only when accelerating, and so on). Ah hah. We now have the beginnings of a diagnostic strategy for dealing with intermittents. Once you’ve established the conditions that are associated with the problem, you have a clue as to what might be causing the problem. Temperature Related Engine Problems If an intermittent starting or driveability problem only occurs when the engine is hot or cold, only during warm-up, only when the engine reaches normal operating temperature, or only when the ambient temperature is high or low, you know that temperature is affecting something. The question is what? Temperature-related intermittents often mean a circuit is shorting out or opening up as a result of thermal expansion or contraction. Heat may be causing a loose or corroded connector or ground to break contact. Microscopic hairline cracks in circuit boards, soldered connections, wiring connectors and even integrated circuits may open up as operating temperatures rise. An injector solenoid or ignition coil that shows normal resistance at room temperature may short out or open up when it gets hot. The same goes for relay coils and contacts. Sometimes diodes and transistors can become flaky at high temperatures and/or voltage loads, too. Temperature effects on electronic components can be simulated with a blow comb or hot air gun. By directing heat at suspicious connections, modules or other components, you can sometimes get the part to misbehave when it gets hot. If so, this would confirm the problem and complete your diagnosis. The next step would be to replace the faulty component. Changes in operating temperature also affect the way the PCM controls spark timing, the fuel mixture and other emissions functions. If an intermittent problem only occurs after the vehicle has been driven several miles, it may be occurring when the PCM goes into closed loop. The underlying cause might be a bad oxygen sensor signal, airflow sensor signal or MAP sensor signal that is upsetting the air/fuel mixture. If a problem seems to occur only when the engine is running in closed loop, that would tell you it’s probably a sensor or PCM-related issue. The strategy here would be to look at some of the key sensor inputs with your scan tool to see if readings are within normal limits. Some problems may occur too quickly for the normal data stream to detect a fault, so you may have to hook up a digital storage oscilloscope to detect a momentary glitch. Temperature also can cause mechanical things to stick as a result of thermal expansion when a part gets hot. Valves and lifters can stick if an engine overheats. EGR valves can stick from heat or a buildup of accumulated carbon deposits. Relay contacts may be affected by changes in temperature, too. One thing to check here is the operation of the cooling system. A low coolant level may prevent the thermostat from opening and closing normally. An inoperative electric fan or a clogged radiator also may allow unwanted fluctuations in engine http://www.aa1car.com/library/2003/us80312.htm
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temperature that affect the way it runs. Motion Related Engine Problems Intermittent problems that only occur when traveling at a certain speed, when driving on a rough road, when hitting a bump, when accelerating or braking, etc., are a pretty good indication that something is loose. The underlying problem may be a loose wiring connector, ground strap, a wiring harness that is chaffing or rubbing against something, or a circuit board with hairline cracks or fractures. Ford’s key on engine off "wiggle tests" are one way to check for loose wires and connectors that may be shorting or opening as a result of movement or vibration. A visual inspection of the wiring and connectors combined with some continuity checks while wiggling or moving wires will often reveal the bad connection. Motion-related intermittent problems also can occur when harmonic vibrations in the exhaust system, driveline or suspension feedback through the powertrain or chassis. This may affect the operation of certain parts or make you think your engine is running rough or making unusual noises. Moisture Related Engine Problems Problems that only occur during damp weather, when it is raining, after driving through a puddle, etc. would tell you water is acting as a conductor and shorting something out.
Moisture on the spark plug wires, distributor cap or coil can cause a no start. The fix is to wipe off the wires and spray them with a moisture repellent such as silicone lubricant or WD-40. When humidity is high, moisture can condense out of the air and form droplets of liquid on any cold surface. If the surface happens to be a distributor cap, ignition coil or spark plug wires, the ignition voltage may find a shortcut to ground instead of following it’s normal path to the spark plugs. Moisture is especially damaging to PCMs and electronic circuit boards. Moisture can cause corrosion that shorts out circuits and causes all kinds of weird electronic problems. That’s why flood-damaged vehicles are so unreliable. Sooner or later, they usually need to have the PCM and/or other electronic modules replaced. No Pattern Intermittent Engine Problems A totally random intermittent is the worst of all to diagnosis. God help you because the only thing you know about the problem is that it doesn't depend on any specific driving or environmental condition. It may occur at any time, at any temperature or any driving situation. If there is no apparent pattern to a problem, how can you duplicate it? The answer is you often can't. The only way to catch these kinds of problems is to keep driving your car until it acts up, then hope you can find some clues as to why the problem is happening. One alternative to the "wait-and-see" diagnostic approach is to take your car to a repair shop that has what's called a flight recorder. This plus into the OBD II diagnostic connector under the dash and records engine data while you drive your car. When the problem occurs, you push a button and the recorder stores a snap shot of the engine data at that moment. The shop can then look at the data on their scan tool or with a PC to hopefully get some insight into what happened and why. Some Intermittent Engine Problem Scenarios
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Scenario #1: An engine starts normally, idles smoothly and runs okay under light load, but misfires erratically when it comes under load or accelerates. The engine is obviously misfiring under load but does not do it all the time. The most likely causes here would be a defective ignition coil, bad plug wires or worn out or fouled spark plugs. When the ignition system comes under load, the spark finds an easier path to ground causing ignition misfire. The coil primary and secondary resistance may both be within specs, but the coil may have hairline cracks or internal shorts that only show up under load. A visual inspection of the ignition system and observing the snap voltage and ignition patterns on a scope can help you identify and isolate the parts that need to be replaced. Scenario #2: An engine starts normally one day, but not the next. It cranks but refuses to start the first or second time, but may start normally after it sits awhile. The condition does not seem to depend on temperature or humidity. Something is obviously disrupting spark or fuel, but what? The trick here is to catch the engine when it is acting up. If there’s no spark, check the crankshaft position sensor or distributor pickup and module. If there is spark, check the injectors and fuel system. Is the fuel pump working? Are the injectors buzzing? No buzz means no injector driver signal from the PCM. The underlying cause might be a bad injector relay, no trigger signal to the PCM or a bad driver circuit inside the PCM. If there’s also no spark and the vehicle is a Chrysler with an ASD (auto shutdown) relay, it’s probably a bad relay because the relay supplies voltage to both the fuel pump and the ignition coil. If the coil, fuel pump and PCM are all hot but there’s no injector signal from the PCM (which you can check for at the injectors with a noid light), the driver circuit in the PCM may be bad - or one of the injectors may be shorted and pulling down the PCM driver circuit. Check the resistance of each injector before you condemn the PCM. If there’s no fuel and the pump isn’t running, the pump may have a loose or corroded wiring connection, or a bad relay. If the vehicle has a safety inertia switch that cuts off the fuel pump in case of an accident, check that too. Scenario #3: An engine starts normally when cold, but has hot starting problems. Check the residual pressure of the fuel system when the engine is shut off. If the system isn’t holding residual pressure, the fuel inside the fuel rail may be boiling from the engine’s heat. The cause here is a leaky check valve in the fuel pump, a leaky pressure regulator, or a leaky fuel injector. Scenario #4: An engine suddenly quits running, but then starts again and runs normally. The cause may be the loss of an important sensor signal such as the crankshaft position sensor signal (distributorless ignition systems) or the ignition trigger signal (engines with distributors). Most of the old Ford Thick Film Integrated (TFI) modules that would quit working when they got too hot have been replaced, but there are still a lot of them on the road. Older GM HEI ignition modules also were prone to this disorder - especially if someone replaced the module in the distributor and forgot to apply the heat sink grease underneath to prevent the module from overheating.
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More Engine Diagnostic Articles: Check Engine Light On Got a Trouble Code? Engine Oil Warning Light On Engine Temperature Warning Light On or Engine Overheating Coolant Leak Car Won't Start (Possible Causes & Quick Checks) Engine Won't Crank or Start Engine Won't Start, No Fuel (Bad Fuel Pump?) Engine Won't Start, No Spark
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Check Engine Light On
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The Check Engine Light (which is actually the Malfunction Indicator Lamp or MIL) alerts you when an emissions-related problem occurs with the engine control system or emission controls on your vehicle. Depending on the nature of the problem, the Check Engine Light may come on and remain on continuously or flash. Some intermittent problems will make the Check Engine Light come on only while the fault is occurring (such as engine misfire). The Check Engine light usually remains on once a fault has been detected, and will remain on to remind you that a problem has occurred that needs to be investigated. An illuminated Check Engine Light can be annoying because you don't know what's wrong, and whether or not the problem might be a serious one or just a minor fault. There is no way to know what the problem is until you plug a scan tool into the vehicle's diagnostic connector and read out the code(s) that turned the light on.
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If no other warning lights are on, and the engine seems to be running normally (no unusual noises, smells, vibrations, etc.), you can assume the fault that is causing the Check Engine Light to come on is probably minor and won't hinder your ability to continue driving. But if other warning lights are on, you should probably stop and investigate the problem. When the Check Engine Light comes on, a diagnostic trouble code (DTC) is recorded in the powertrain control module (PCM) memory that corresponds to the fault. Some problems can generate more than one trouble code, and some vehicles may have multiple problems that set multiple trouble codes. CHECK ENGINE LIGHT ON SETS TROUBLE CODES In most older vehicles (those made before 1996), disconnecting the computer's power source or disconnecting a battery cable erases fault codes and turns off the Check Engine Light, at least temporarily. If the problem persists, the code will reset and the Check Engine Light will come back on. But on many newer vehicles, you do NOT want to disconnect the battery because doing so can wipe out the computer's memory settings. This may affect the operation of the transmission, climate control system and other functions. In 1996 and newer vehicles, a scan tool or code reader must be used to erase codes and turn the Check Engine Light off. HOW TO READ FAULT CODES WITH A SCAN TOOL If your Check Engine light is on, you need to read the code(s) that are causing it to come on with a code reader or scan tool. Plug the tool into the 16-pin OBD diagnostic connector (usually located under the dash near the steering column). When the ignition is turned on (don't start the engine yet), the tool will communicate with the PCM. You may be asked to enter the year/make/model and VIN code of your vehicle if the scan tool does not automatically recognize the application. Choose the READ FAULT CODE option on the scan tool menu, or press the button that allows the tool to read the codes. The tool will then display a number and/or code description that corresponds to a particular fault code. The letter "P" is the designation for Powertrain codes (which includes all of the engine controls, related emission controls, catalytic converter and fuel tank vapor control system). If there are more than one code, the codes will be listed in numeric order. TIP: Write the code(s) down on a piece of paper before you erase them. You may need to refer to the codes again later if the same problem keeps returning. Erasing the codes will turn the Check Engine Light off, but sooner or later the codes will likely return and turn the Check Engine Light back on again if the problem is still there. For a list of the Most Common Fault Codes and what causes them, Click Here. For general diagnostic tips on what can set various types of fault codes Click Here. Important! A fault code will tell you which sensor or system experienced some kind of problem. But the code will NOT tell you why the fault occurred, how bad the fault is or which part to replace. That usually requires more advanced diagnostics. For additional help with specific fault codes, see the related articles on the AA1Car website or refer to the list of sensor and emissions-related articles below for more information about these components and systems: Making Sense of Engine Sensors (overview of the different types of sensors and what they do) Air Temperature Sensors Coolant Sensors Crankshaft Position CKP Sensors Oxygen (O2) Sensors Oxygen Sensor Locations Wide Ratio Air Fuel (WRAF) Sensors Sensing Emission Problems (O2 Sensors) MAP sensors
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Mass Airflow MAF Sensors Vane Airflow VAF Sensors Throttle Position Sensors Understanding Engine Management Systems CHECK ENGINE LIGHT ON DIAGNOSTICS Prior to OBD II, fault detection was mostly limited to "gross failures" within individual circuits or sensors. The first generation systems were not capable of detecting misfire, converter problems or fuel vapor leaks. OBD II changed all of that by adding the ability to monitor these things so emission problems can be detected as they develop. OBD II uses the Check Engine Light to alert the driver when a fault occurs, and it stores trouble codes that correspond to specific kinds of problems. It can also track problems as they develop and even capture a snapshot of sensor data when a problem occurs. Almost any emission problem that causes hydrocarbon emissions to exceed 1.5 times the federal limit can cause the Check Engine Light to come on with OBD II, even if there is no noticeable drivability problem accompanying the emission problem. OBD II not only monitors the operation of all the engine's sensors and systems (fuel, ignition, EGR, evaporative emissions, etc.), it also monitors the operation of the catalytic converter and can even detect engine misfires! Anything that could possibly affect emissions is monitored by OBD II, including a loose gas cap! For more information about the OBD monitors and their ready status, Click Here. For a detailed look at the operating parameters that can set various fault codes, Click Here to view a PDF file on GM 4.6L diagnostic parameters. UNDERSTANDING DIAGNOSTIC TROUBLE CODES A misfire will cause the Check Engine Light to flash while the misfire is occurring. A misfire that occurs in a given cylinder will also set a P030X code where "X" will be the number of the cylinder that is misfiring. For example, a P0302 code would tell you cylinder number two is misfiring. Remember, the code does not tell you why the cylinder is misfiring. You have to figure that out by performing other diagnostic tests. The misfire might be due to a fouled spark plug, a bad plug wire, a defective ignition coil in a DIS ignition system, a clogged or dead fuel injector or a loss of compression due to a leaky exhaust valve, leaky head gasket or worn cam lobe. OBD II monitors the operating efficiency of the catalytic converter with a second oxygen sensor in the tailpipe behind the converter. By comparing upstream and downstream O2 sensor readings, it can determine how well the converter is doing its job. If converter efficiency drops below a certain threshold, OBD II will set a code and turn on the Check Engine Light. OBD II can detect fuel vapor leaks (evaporative emissions) in the charcoal canister, evap plumbing or fuel tank by pressurizing or pulling a vacuum on the fuel system. If the gas cap is loose or missing, it will detect it, set a code and turn on the Check Engine Light. In addition, OBD II can also generate codes for various electronic transmission problems and even air condition failures such as a compressor failure. TWO KINDS OF FAULT CODES OBD II is capable of generating two types of diagnostic trouble codes: "Generic" or "Global" codes (P0) that are the same for all makes and models of vehicles (these are required by law), and "Enhanced" or "OEM" codes (P1) that are unique to specific vehicles. Enhanced codes can also cover non-emission related failures that occur outside the engine control system. These include ABS codes, HVAC codes, airbag codes and other body and electrical codes. The "generic" codes that are common to all vehicle manufacturers can be accessed using any basic code reader or scan tool that is OBD II compliant. Unfortunately, most older scan tools made before 1995 won't work on 1996 and newer vehicles with OBD II. You need a scan
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tool that has the proper hardware and software to talk to your onboard computer so it can read OBD II codes and other diagnostic information. In fact, a scan tool or code reader is required to read codes on most 1996 and newer vehicles because most newer vehicles do not have manual flash codes. There are some exceptions. Some Nissan models still provide manual flash codes, as do some Dodge models. Most GM, Ford, Honda and Toyota models do not have flash codes, but on some GM vehicles with a driver information display, there may be a procedure for displaying codes manually.
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A simple code reader that plugs into the vehicle diagnostic connector can usually be purchased at an auto parts store for under $60. A basic scan tool that can read codes and additional system data (and erase codes) may sell for $70 to $400 depending on its features. The kind of scan tools that professional technicians use can cost several thousand dollars and have more advanced features, including bidirectional capabilities that allow the scan tool to run various self-tests that are built into the engine management system on your vehicle. These types of advanced tests may be required for more difficultto-diagnose problems. The high end professional level scan tools can also graph sensor voltages, allowing them to reveal diagnostic data that a simple DIY scan tool cannot. If you do not have a code reader or scan tool, you will have to take your vehicle to a repair facility or auto parts store if you need to diagnose a Check Engine Light problem. Money Saving Tip: Some parts stores (such as AutoZone and others) will do a FREE plug-in diagnosis for you, or they will loan you a scan tool so you can do the basic diagnosis yourself in the parking lot. The scan tool will tell you what the codes are that turned on your Check Engine Light. Just remember that a code by itself does NOT tell you which part may need to be replaced. Additional diagnostic tests are usually needed to determine the underlying cause that set the code. For example, a P0300 Random Misfire Code means the engine is misfiring in multiple cylinders but it doesn't tell you why it is misfiring. The cause could be fuel, ignition or compression, or any combination thereof. Additional tests are needed to identify the cause of the misfire.
YOUR VEHICLE WON'T PASS AN OBD PLUG-IN EMISSIONS TEST WITH A CHECK ENGINE LIGHT ON If your Check Engine Light is on, your vehicle will NOT pass an OBD plug-in emissions test. So if you are required to take such a test, the light must be out and there must be no codes in the PCM memory. You can't just erase the codes, drive your vehicle to the test station and take the test if the original problem is still there. The OBD II monitors need time to set, which usually requires driving at various speeds, sometimes over a period of several days. The OBD plug-in test checks to see if all of the monitor self-tests have completed, and if they have not your vehicle is rejected for not being ready. See OBD Monitors Not Ready. The OBD plug-in test also determines if your Check Engine light is functioning properly. if the lamp is burned out or has been disabled, your vehicle will be rejected until the bulb is replaced or the problem has been fixed. If the test finds any DTCs (Diagnostic Trouble Codes), your vehicle will fail the emissions test. The test center should give you a print out that lists any codes found along with possible suggestions as to what may be causing the fault(s). You must then have your vehicle repaired (which you can do yourself if you have the tools and know-how to do) or you can take it to a repair shop or new car dealer to have the problem fixed. Some states maintain a website (such as the Illinois Clean Air Team) that rates repair shops by their success rate at fixing emission faults. If you don't know where to take your car for repairs, these websites can be very helpful. SEMA eNews Update: May 16, 2007
EPA TARGETS ILLEGAL CHECK ENGINE LIGHT ELIMINATOR DEVICES The U.S. Environmental Protection Agency (EPA) is investigating sales of devices which can turn off the check engine light when O2 sensor readings are not operating properly. Both the EPA and the California Air Resources Board (CARB) have been more aggressive in recent years in removing such products from the marketplace since they can easily be used on the
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highway but are usually advertised for off-road use or racing-use only. These items are commonly referred to as defeat devices since they can render inoperative a portion of the emissions control system. Manufacturers, distributors and retailers of MIL eliminator devices could face charges of violating the Clean Air Act. The agency has authority to seize and destroy these products and issue fines. Subsection (B) of 42 USC Sec. 7522 (1990 Clean Air Act Amendments) makes it illegal for any person to manufacture or sell, or offer to sell, or install, any part or component intended for use with, or as part of, any motor vehicle or motor vehicle engine, where a principal effect of the part or component is to bypass, defeat, or render inoperative any device or element of design installed on or in a motor vehicle or motor vehicle engine in compliance with regulations under this subchapter, and where the person knows or should know that such part or component is being offered for sale or installed for such use or put to such use;
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Related Articles: Most Common Trouble Codes (and what causes them) Fault Codes and What Causes Them More on Check Engine Lights & Fault Code Diagnostics Ford P0171 & P0174 Lean Codes 5 Warning Lights You Should Never Ignore! Other Warning Lights (TEMP, OIL, ALT/GEN, BRAKES, ABS, AIR BAGS, etc.) Scan Tool Help Scan Tool Diagnostics Decoding Onboard Diagnostics TROUBLE CODES Help Understanding OBD II Driveability & Emissions Problems Zeroing in on OBD II Diagnostics OBD Monitor Not Ready Controller Area Network (CAN) Diagnostics Troubleshooting Intermittent Engine Problems OBD II Diagnostic Tips Mode 06 Onboard Diagnostics (advanced diagnostics) Help with DTC P0300 Random Misfire Codes Troubleshooting a P0420 Catalyst Fault Code
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Diagnose Check Engine Light Copyright AA1Car.com
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. The Check Engine light, which is officially called the "Malfunction Indicator Lamp" (MIL) alerts you when your vehicle's OBD II system has detected a potential emissions problem. Depending on the nature of the problem, the Check Engine lamp may come on and go off, remain on continuously or flash. Of course, none of this gives you any clue whatsoever as to what might be going on. Some people panic when they see the light, fearing their engine is experiencing some kind of major problem. But fear not, because in most instances, the problem is usually minor and is nothing that requires your immediate attention. Here's how the Check Engine Light works. When the OBD II system detects any fault that may cause an increase in emissions, it sets a "pending code" in the computer's memory. The Check Engine Light doesn't come on yet because the system needs to make sure the problem is real and not a temporary glitch. If the same problem occurs on a second trip (under the same driving conditions), the OBD II system will then set a diagnostic trouble code (DTC) and turn on the Check Engine Light.
What To Do If Your Check Engine Light Is On If no other warning lights are on (temp, oil pressure, charging, etc.), AND your vehicle is driving normally (no unusual sounds, smells, vibrations, loss of power or other signs of trouble), you don’t have to do anything immediately. But you need to find out why the light came on when it is convenient to do so.
Use a Scan Tool The only way to know why your Check Engine light is on is to connect a scan tool or code reader to the 16-pin OBD II diagnostic connector under the instrument panel and read out the code. If you do not have a code reader or scan tool to do this yourself, you can take your car to an auto parts store for a free diagnosis (Autozone & Advance Auto are currently offering this). If you can’t get a free diagnosis at an auto parts store, you will have to take your vehicle to a repair shop or new car dealer for a plug-in diagnosis. Be warned that this is usually expensive. Most charge $75 or more to perform this service. For the same money, you could buy a code reader or basic scan tool and do it yourself.
Reading Trouble Codes When you plug a code reader or scan tool into the diagnostic connector, the tool will display any trouble codes that are in the http://www.aa1car.com/library/2003/cm70336.htm
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powertrain control module (PCM) memory. There may be only one code, or there may be multiple codes. Basic code readers may only display a number, which you then have to look up in a reference book or online to find out what it means. Better scan tools display the trouble code number and a short definition of what the trouble code means. Write down any trouble codes and definitions that are displayed for future reference. What you do next will depend on the code(s) your found. A trouble code by itself does not tell you what part needs to be replaced. It only tells you the circuit or component where the fault occurred (oxygen sensor, for example), or the nature of the fault (misfire, for example). See Trouble Code Diagnostic Help for Types of Codes for additional information on how to diagnose and repair common trouble codes.
Further diagnosis is usually necessary to isolate the fault and figure out what is causing the problem and which part (if any) needs to be replaced. This often requires following a lengthy diagnostic chart and step-by-step checks to rule out various possibilities. This kind of information can be found in the vehicle service literature or on AlldataDIY. For example, let's say your Check Engine Light is on and you find a trouble code for one of the oxygen sensors (code P0130). The code might indicate a bad sensor, or it might indicate a loose connector or wiring problem. You should check the wiring first before replacing the sensor. Harder to diagnose are misfire codes. OBD II can detect misfires in individual cylinders as well as random misfires. If it generates a misfire code for a single cylinder (say P0301 for the #1 cylinder), it only tells you the cylinder is misfiring, not why the cylinder is misfiring. The underlying cause could be a bad spark plug, a bad plug wire, a weak coil on a distributorless ignition system (DIS) or coil-on-plug (COP) system, a dirty or dead fuel injector, or a compression problem (bad valve, leaky head gasket, rounded cam lobe, etc.). As you can see, there are multiple possibilities so it takes some diagnostic expertise to isolate the fault before any parts can be replaced. A "random misfire code" (P0300) is even harder to diagnose because there can be numerous causes. A random misfire usually means the air/fuel mixture is running lean. But the cause might be anything from a hard-to-find vacuum leak to dirty injectors, low fuel pressure, a weak ignition coil(2), bad plug wires or compression problems. For a detailed look at all the operating parameters that can set trouble codes, Click Here to view a PDF file on GM 4.6L diagnostic parameters. The best advice in situations like this is to take your car to a repair facility that has the proper tools and expertise to accurately diagnose the fault.
Watch Out for False Codes Sometimes circumstances will set a code that indicates a fault has occurred, but actually there is no real problem. Some cars will set codes because the OBD II system is over-sensitive or there is a glitch in the factory software. For example, older GM cars with certain 3.8L engines will often set a P1406 code, which indicates a fault in the EGR valve. Replacing the EGR valve doesn't fix the problem on these cars because the OBD II system is overly sensitive to how quickly the EGR valve opens when it is commanded to do so by the PCM. The cure here is not to replace the EGR valve, but to have your car dealer or repair shop reprogram your engine computer. This is called "reflashing the PCM" and it involves installing updated software that fixes the problem. The process typically takes about a hour and costs $100 to $200. Vehicle manufacturers frequently release Technical Service Bulletins (TSBs) that provide fixes for faults like these. This type of information is available on the vehicle manufacturer’s service information website, or through Alldata.
Turning The Check Engine Light Off The OBD II Check Engine light will generally remain on as long as a fault persists. If an intermittent fault does not reoccur after three consecutive trips, the MIL lamp will go out, but the trouble code will remain in memory. If the
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fault does not reoccur for for 40 to 50 trips, the code will be erased. The only safe way to clear fault codes and turn of the Check Engine Light is to use a scan tool or code reader. Most of these tools have a button or menu choice that says "Clear Codes?" When you press the button or choose the option, it wipes the code from the PCM's memory. This will take you back to ground zero. ADVICE: Write down any codes you have found BEFORE you erase them! Don't think you'll remember them because in a few days you probably won't.
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If the Check Engine Light comes back on again (which is usually does if there is a hard fault in the system), you can check the codes again to see if they are the same ones as before. This would confirm the fact that you have an emissions problem, and that further diagnosis and repairs are probably necessary.
NOTE: Many emission faults that sets codes won't have any noticeable effect on the way your car starts, drives or behaves. So you may be tempted to just ignore them. That's up to you. But if you live in an area that requires emissions testing, your vehicle will NOT pass an emissions test if the Check Engine Light is on. On older pre-OBD II vehicles (1995 and back), trouble codes can also be cleared from the PCM's memory by disconnecting the battery. Unhooking the battery ground cable for 10 seconds, then reconnecting it will "reset" the computer. But it will also wipe all of the other learned settings from the PCM's memory, too. That means your engine may not idle smoothly or feel quite right for some time until the PCM relearns what it needs to know. Same for the transmission controller. You will also lose the channel presets on the radio, and any other electronic settings (memory seats, mirrors, etc.). That's why a code reader or scan tool should be used to clear the codes only. WARNING: On many 1996 and newer OBD II cars, pulling the PCM fuse or disconnecting the battery may NOT clear the codes, and may cause a loss of important information the PCM needs to function correctly. This is certainly true on 2004 and newer vehicles with Controller Area Network (CAN) electrical systems. DO NOT DISCONNECT THE BATTERY ON THESE VEHICLES! On some vehicles, loss of power to the PCM may cause it to forget transmission settings, climate control functions and other essential data. This, in turn, may require an expensive trip to the new car dealer so they can use a factory scan tool to reset or reprogram the information that was lost. Check Engine Light On? Need Help Now? Click the Banner Below to Ask an Expert:
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Ford P0171 & P0174 Lean Codes
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Ford P0171 & P0174 Lean Codes Copyright AA1Car A Ford P0171 is a LEAN code for cylinder bank 1, and P0174 is a LEAN code for cylinder bank 2. These codes commonly occur on many Ford vehicles, and are set when the powertrain control module (PCM) sees the air/fuel mixture is running too lean (too much air, not enough fuel). When the Check Engine Light comes on, either one of these codes, or both, may be found when a code reader or scan tool is plugged into the vehicle diagnostic connector. IF the vehicle is driven long enough, typically both codes will be set. A P0171 lean code for bank 1 is the cylinder bank on the RIGHT (passenger) side of the engine on Ford vehicles with a V6 or V8 engine and rear-wheel drive. A P0174 lean code for bank 2 is the cylinder bank on the LEFT (driver) side of the engine on Ford vehicles with a transversemounted V6 engine and front-wheel drive. This code is not set on four cylinder engines (no bank 2).
WHAT A LEAN CODE MEANS A lean fuel condition may exist if the engine is sucking in too much air and/or the fuel system is not delivering enough fuel. If bad enough, a lean fuel condition may cause lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine performance. Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow). If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator or dirty fuel injectors. http://www.aa1car.com/library/ford_lean_codes.htm
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DIRTY MAF SENSOR One of the most common causes of Ford P0171 and P0174 lean codes is a dirty mass airflow (MAF) sensor. The MAF sensor is located in the air inlet tube just ahead of the throttle body. The MAF sensor should be protected from outside dust and debris by the air filter, but sometimes the air filter doesn't fit real tight inside the housing and allows unfiltered air into the engine. Dirt can stick to the MAF sensor wire and form a coating that slows the response of the sensor to changes in airflow. The MAF sensor can also be contaminated by fuel vapors that back up through the intake manifold and throttle body when the engine is shut off. The vapors can leave a waxy coating on the sensor wire. This causes the MAF sensor to under report airflow, which in turn misleads the powertrain control module (PCM) so it doesn't add enough fuel to maintain a properly balanced air/fuel ratio. As a result, the engine runs lean and sets a P0171 and/or P0174 code (see Ford TSB 98-23-10 for details). One way to diagnose a dirty MAF sensor is to hook up a scan tool, choose the PID data menu and look at fuel trim values while the engine is running. If the MAF sensor is dirty, the fuel trim at idle will probably be close to normal (plus or minus 3 to 5 range), but as engine speed increases up to 2500 RPM, you will see the fuel trim value go positive (5 or higher). If the MAF is dirty, the fix is easy enough: just clean or replace the MAF sensor. In many instances, the MAF sensor can be successfully cleaned by spraying the sensor element with electronics cleaner. Do not use any other type of cleaner as this may damage the sensor. Disconnect the air inlet tube just ahead of the sensor, and then spray the electronics cleaner through the screen at the wire element in the center of the little MAF sensor. Let the cleaner soak in for several minutes, then give it another shot of cleaner. Let it sit another five minutes, then reconnect the air inlet tubing and start the engine. If the lean codes keep coming back, the MAF sensor may have to be replaced if the engine does not have a vacuum leak or fuel delivery problem.
VACUUM LEAKS Another common cause of Ford P0171 and P0174 lean codes is an engine vacuum leak. Vacuum leaks can occur anywhere in the intake plumbing downstream of the throttle body (throttle body gasket, intake manifold gaskets or vacuum hose connections to the intake manifold)
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You can use a scan tool to diagnose a vacuum leak. Plug in your tool, sart the engine and choose the PID data menu. Look at the fuel trim values at idle. If there is a vacuum leak, the fuel trims will be positive (probably 5 or higher). Now rev the engine to 2500 RPM. If the cause is a vacuum leak, the leak will have less effect at higher engine speed and load, and you should see the fuel trim values drop back closer to normal (closer to zero, plus or minus 3 or 4). Ford TSB 04-17-4 details procedures for checking fuel trim and looking for vacuum leaks. On 3.8L Fords with a split-plenum intake manifold, the port gaskets and isolator bolt assemblies for the upper plenum can deteriorate over time and leak air, often as a result of oil being sucked into the intake manifold through the PCV system. Also the vacuum hose that connects the fuel pressure regulator to the intake manifold can swell and leak vacuum where the hose connects to the manifold. Ford TSB 03-16-1 says the fix involves several steps: remove the upper manifold plenum and replace the original gaskets and bolts with revised ones, replace the front valve cover with a revised valve cover that reduces the amount of oil vapor sucked into the PCV system, inspect and replace the fuel pressure regulator hose, and finally, reflash the PCM so it is less sensitive to lean fuel conditions.
LOW FUEL VOLUME DELIVERY Lean codes can also be set if the engine is not getting enough fuel. The underlying cause might be a weak fuel pump, low voltage to the fuel pump (which prevents the fuel pump from spinning fast enough to deliver normal fuel flow), a restricted fuel filter, or possibly a leaky fuel pressure regulator. See Diagnose Fuel Pump for more information on how to troubleshoot fuel delivery problems. You can also use a scan tool to diagnose fuel delivery problems that may be causing a lean code. Hook up your scan tool, go to the PID data menu and look at the fuel pressure PID. If fuel pressure is less than specifications, there is probably a problem in the fuel pump or fuel pump wiring circuit. Next, look at the fuel trim values while the engine is running. At idle, the fuel trim may be normal to slightly positive. If your engine has a fuel delivery problem, the fuel trim values will become more positive as engine speed and load increase. No change in fuel trim values would tell you the engine is getting enough fuel and that low fuel volume is NOT the cause of your lean code. Dirty fuel injectors can have the same effect as a weak fuel pump. They may flow enough fuel at idle and low speed to keep up with engine demand, but at higher engine speeds and loads, they may not spray enough fuel to maintain the proper air/fuel ratio. The effect on fuel trim would be the same as a weak fuel pump - close to normal at idle but going more positive (indicating a lean fuel mixture) as engine speed and load increase. The fix for dirty fuel injectors is to clean the injectors. Fuel tank additives can be slow or ineffective if the injectors are really dirty, so it may be necessary to have the injector professionally cleaned.
BAD DPFE SENSOR Ford p0171 AND p0174 lean codes can also be set by a bad EGR differential pressure sensor. These sensors have a very high failure rate once a vehicle has more than about 60,000 miles on the odometer or is more than five or six years old. The DPFE sensor is mounted on the engine, and is attached with two rubber hoses to the tube that routes exhaust gas to the EGR valve. The original equipment sensor has an rectangular aluminum housing about three inches long. Corrosion inside the sensor reduces its sensitivity to EGR flow, causing it to under-report EGR flow. The PCM responds by increasing EGR flow, which may keep the EGR valve open longer than usual creating a lean condition in the engine. Thus, a bad sensor may set a P0401 code (insufficient EGR flow), or it may not set an EGR code but a P0171 and/or P0174 lean code instead. The cause of the P0401 code in most cases turns out to be a bad DPFE sensor, not an EGR valve problem or an EGR valve
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that is plugged up with carbon (though this can also set a P0401 code). An aftermarket replacement DPFE sensor costs less than $50 and usually gets rid of not only the P0401 code, but also the P0171 and P0174 codes, too.
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5 Warning Lights You Should Never Ignore
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5 Warning Lights You Should Never Ignore! Copyright AA1Car
If any of the above warning lights come on while you are driving, DO NOT IGNORE THEM! Immediate action may be necessary to prevent damage to your vehicle, a breakdown or an accident.
OIL PRESSURE WARNING LIGHT The oil pressure warning light comes on if your engine has lost oil pressure or oil pressure is too low for safe engine operation. You should pull over to the side of the road, shut the engine off and check the oil level on the engine dipstick. Possible Causes: Low oil level (due to oil consumption or leaks), oil viscosity too thin, worn oil pump, excessive engine bearing clearances or defective oil pressure sending unit. If you engine is also making ticking, clattering or rapping noises, it is not getting sufficient oil. If you attempt to drive the engine in this condition, you will probably damage it - if it hasn't already suffered major internal damage. For more information about your engine's lubrication system and causes of low oil pressure, Click Here.
TEMPERATURE WARNING LIGHT The temperature warning light will come on if your engine is overheating. Do NOT continue driving if your engine is overheating as this can cause expensive engine damage (piston scuffing, valve stem galling, failed head gasket, cracks or distortion in cylinder head). Stop driving, pull over and shut your engine off. Open the hood and check the radiator and heater hoses, radiator and engine for coolant leaks. Note the level of the coolant in the coolant reservoir. CAUTION: DO NOT open the coolant reservoir or radiator cap until the engine has cooled off for at least 30 minutes. Steam pressure inside the cooling system can blow out and burn you! If the coolant level is low, add coolant (a 50/50 mixture of antifreeze and clean distilled water) after the engine has cooled down. Possible Causes: Low coolant level (due to coolant leak or bad head gasket), stuck thermostat, bad water pump, broken
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serpentine belt, defective radiator cooling fan, clogged or dirty radiator, exhaust restriction (plugged catalytic converter). HINT: Turning the A/C OFF and turning the heater on HIGH may help cool down an engine that is temporarily overheating due to unusually hot weather or from towing a trailer. But if the engine is running hot because it is low on coolant, this trick probably won't help much. For more information about troubleshooting an overheating problem, Click Here.
CHARGING SYSTEM WARNING LIGHT The "GEN" or "ALT" warning light, or an icon of a battery will illuminate if the charging voltage in your vehicle is low. You do not have to stop immediately, but you may only have 20 to 30 minutes of driving time before your battery goes dead and your engine stops running (or even less time if you are driving at night with your headlights on). Possible Causes: Broken or slipping serpentine belt or V-belt, bad alternator, charging control fault, or loose or corroded battery cables. Open the hood to see if the drive belt that turns the alternator is intact and is turning the alternator while the engine is idling. If the belt is not the problem, chances are the charging system has a problem that will have to be diagnosed and repaired. Better find a repair shop soon! For more information about the operation of the charging system and charging diagnosis, Click Here.
BRAKE WARNING LIGHT The Brake Warning light will come on if the parking brake has not been fully released, but it may also come on if the brake fluid level is low or there has been a loss of hydraulic pressure in one of your car's brake circuits. Loss of fluid or brake pressure means the brakes may not be able to stop your car when you step on the pedal. Carefully apply the brakes to see if they are working. If they are, pull over to the side of the road, open the hood and check the fluid level in the brake master cylinder. If the fluid level is low, the brake system should be inspected for leaks. If there are leaks, your brake system is unsafe to drive. If the brake pedal is low or goes to the floor, pumping the pedal may apply enough pressure to stop your car. If that fails, apply your parking brake to slow your vehicle. Also, take your foot off the gas and shift to neutral, or downshift and use engine braking to slow your vehicle if you have a manual transmission. If all that fails, aim for something soft like a bush or open field. Possible Causes: Loss of brake fluid due to leaks (master cylinder, calipers, wheel cylinders, brake lines or hoses), failure of the pressure differential switch that activates the brake light, parking brake pedal or handle not fully releasing, defective parking brake switch. WARNING: If the brake pedal feels soft, is low, goes to the floor, or you have to pump the pedal to get your vehicle to stop, your vehicle is unsafe to drive. You should have it towed to a repair facility for repairs. For more information about brake problems, Click Here.
LOW TIRE WARNING LIGHT The Low Tire Pressure Warning Light will come on if any tire on your vehicle is 25 percent or more underinflated. Driving on a low tire can be dangerous because it increases the risk of a tire blowout. A low tire can also cause uneven braking, uneven traction, uneven and rapid tire wear, increased rolling resistance and fuel consumption.
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5 Warning Lights You Should Never Ignore
Find a gas station with an air pump, and check the inflation pressure in each tire with an accurate gauge (not the gauge on the pump, which is often very inaccurate!). Add air as needed to inflate your tires to the recommended pressure (see your owners manual or the tire inflation decal in teh door jam or glove box). For most passenger cars, the recommended pressure is typically 32 to 34 PSI. Possible Causes: Loss of air pressure due to a leak (such as a nail or small puncture in a tire, or a bad valve stem), loss of air pressure due to seepage (1 to 2 PSI per month loss is normal for many tires), or inaccurate or failing TPMS sensor in tire. Checking your tires regularly (at least once a month or before any long road trip) is recommended. Check the tires when they are COLD and BEFORE you drive your vehicle as driving creates friction and heats up the tires (causing an increase in air pressure). For more information about the TPMS Warning Light, Click Here For more information about the Tire Pressure Monitor System, Click Here. For more information about Tire Inflation Tips, Click Here.
MORE WARNING LIGHTS Many vehicles have their own unique warning lights or icons to alert you when something is wrong. You can usually find these in the back of your vehicle owners manual. Note: The appearance of some warning lights will vary depending on the country where the vehicle is sold. Below are some typical warning lights for a late model Lexus (courtesy Toyota):
Click on image above to increase size.
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Dash Warning Lights
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Dash Warning Lights Copyright AA1Car
CHECK ENGINE LIGHT Also called the "Malfunction Indicator Lamp" or (MIL), an illuminated CHECK ENGINE LIGHT means you vehicle has detected a potential emissions fault. The computer has logged one or more diagnostic trouble codes that correspond to the problem and turned on the warning lamp to alert you to the problem. There is NO WAY to determine the nature of the problem without connecting a scan tool to the vehicle's diagnostic connector to read the fault code(s). Once this has been done, further diagnosis and testing may be required to isolate the fault so the correct parts(s) can be replaced. Don't be alarmed by a CHECK ENGINE light. Often the problem is something minor that will NOT affect the way your engine runs, or you car's ability to start or drive. Depending on the nature of the fault, your engine may not run as good as it normally does, or it may use more fuel than usual. But usually the problem does NOT require immediate attention. You can continue to drive your car until it can be diagnosed. Common reasons for the CHECK ENGINE light to come on include a loose gas cap, fouled spark plugs, dirty fuel injectors, the failure of an engine sensor such as the oxygen sensor, throttle position sensor or manifold absolute pressure sensor, or a problem in an emissions control system or device such as the EGR valve or catalytic converter. For more information about CHECK ENGINE light problems, Click Here. For more information about troubleshooting Check Engine Codes with a scan tool, Click Here..
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OIL PRESSURE WARNING LIGHT If a warning light says OIL or you see a little icon of an oil can, DO NOT ignore this warning light. It means your engine is not getting normal oil pressure. Stop driving immediately, turn the engine off and check the engine's oil level. If low, add oil to bring the level up to the FULL mark on the dipstick. The oil pressure warning light comes on when oil pressure drops below a minimum threshold (the exact pressure will vary from one vehicle to another). No engine will run very long if it runs out of oil. The bearings will run dry, overheat and seize, causing severe engine damage (spun bearings, damaged crankshaft journals, broken connecting rods, etc.). The underlying cause of a low oil pressure warning light is usually a low oil level in the engine's crankcase. This, in turn, may be due to leaky gaskets or seals, or worn valve guides, piston rings and/or cylinders that are causing the engine to burn oil. Leaky gaskets and seals are usually not too expensive to replace (except for the rear main crankshaft seal which is difficult and expensive to replace). The only fix for a worn engine that is burning oil is to overhaul or replace the engine (very expensive!) Other causes of an low oil pressure warning light include a worn oil pump or a faulty oil pressure sending unit. For more information about your engine's lubrication system and causes of low oil pressure, Click Here.
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TEMPERATURE WARNING LIGHT A TEMP warning light or an icon of a thermometer is another warning lamp that you should NOT ignore. Stop driving immediately, turn the engine off and let the engine cool for at least 30 minutes. Then check the coolant level in the coolant reservoir or radiator. CAUTION: DO NOT open the radiator cap on a hot engine. Hot water and/or steam can spray out and scald you. The temperature warning lamp is on because your engine overheated. Continuing to drive can cause expensive engine damage (head gasket failure, cracks in the cylinder head, piston scuffing, valve stem galling, etc.) Your engine may have overheated for a variety of reasons. The most common cause is a low coolant level (check the radiator, hoses and engine for coolant leaks). Other common causes include a stuck thermostat, a cooling fan that is not working, a failed water pump, obstructions that block airflow through the radiator (bugs, debris, plastic bags), a buildup of scale or sludge inside your cooling system, or overworking your engine or air conditioning system during unusually hot weather. Towing a heavy trailer or prolonged mountain driving may also cause your engine to run hotter than normal.
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If the coolant level is low, add coolant after the engine has cooled off. Check for leaks. If you see none, start the engine and cautiously proceed. If the engine starts to overheat again, your engine may have an internal coolant leak (Bad news because it means a leaky head gasket or cracks in the cylinder head or block), or there is some other problem (bad thermostat, water pump, etc.). If you see a coolant leak, you may be able to temporarily stop the leak by adding a can of cooling system sealer to the radiator. This may temporarily plug the leak or slow it down enough so you can continue driving until the leak can be fixed. For more information about your cooling system and causes of a temperature warning light, Click Here.
CHARGING SYSTEM WARNING LIGHT The "GEN" or "ALT" warning light, or an icon of a battery usually means trouble (on some vehicles, a battery icon may illuminate if there is a charging system problem). You do NOT have to stop immediately, but your drive time will be limited: maybe 30 minutes or so during the daytime, or less after dark. The reason for this is that your car will be running off the battery alone, so as long as the battery lasts you can continue to drive. Eventually, the battery will go dead causing your fuel pump and/or ignition system to stop working. To maximize your remaining drive time, turn off all accessories to minimize the electrical drain on the battery. If you're driving at night, DO NOT turn off your lights (too dangerous!). Pull off at the first opportunity and seek help. This warning light comes on when the charging system is NOT producing enough current or voltage to meet your vehicle's electrical needs. The cause may be a failed alternator or generator, a failed voltage regulator (if separate from the alternator), loose or corroded battery cables, or a broken or slipping drive belt. Turn the engine off and check the belt that turns the alternator. Caution: DO NOT get your fingers, clothing or tools near the belt(s) or pulleys while the engine is running. If the belt appears to be intact and is turning the alternator, start the engine, and turn on the headlights. If the lights are dim, it verifies the charging system is not working -- probably due to a failed alternator or other electrical fault. For more information about the operation of the charging system and charging diagnosis, Click Here.
BRAKE WARNING LIGHT More bad news -- but not always. The Brake Warning light may be one for one of two reasons: you forgot to release the parking brake, or your brake system has a potentially serious hydraulic problem that may make your vehicle unsafe to drive. First, check the parking brake lever, handle or pedal. Make sure it is fully released. If that is not the problem, test the brakes by pressing on the brake pedal. If the light comes on only while pressing the pedal, it means one of the hydraulic circuits in the brake system has lost pressure -- probably because of a leak (bad brake hose, leaky disc brake caliper or drum brake wheel cylinder). Your vehicle may or not be able to stop with this kind of problem, making it unsafe to drive. If the pedal feels unusually low or goes to the floor, DO NOT attempt to drive the vehicle. Have it towed to a service facility for repairs (or fix it yourself). If the Brake Warning light remains on all the time, the problem may be a low fluid level in the master brake cylinder reservoir. Many vehicles have a fluid level sensor that comes on if the fluid level gets low. This may also occur when braking hard or braking on an incline because of the fluid sloshing inside the reservoir. Check the brake fluid level and add fluid as needed if low. The brake system should also be inspected for leaks or worn linings. For more information about brake problems, Click Here.
ABS WARNING LIGHT This warning lamp means your antilock brake system has detected a fault. When this happens, the ABS system logs one or more fault codes that correspond to the problem and turns on the ABS warning light. In most cases, it also temporarily DISABLES your ABS system. You vehicle should still brake and stop normally, but it will NOT have antilock braking when making a sudden panic stop or braking on wet or slick surfaces. You can continue driving, but you should have the problem diagnosed and repaired at your earliest convenience. NOTE: If the Brake Warning light is also on, it may indicate a serious hydraulic problem with the brake system. Your vehicle may NOT be safe to drive (see the info on Brake Warning Light above). For more information about ABS, Click Here.
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LOW TIRE WARNING LIGHT This icon is a Low Tire Pressure Warning light. This light comes on if your vehicle's tire pressure monitoring system (TPMS) detects a tire that is more than 25 percent underinflated. Driving on a low tire can be dangerous because it increases the risk of a tire blowout. A low tire can also cause your vehicle to brake unevenly, pull to one side, handle poorly and get reduced fuel mileage. If the TPMS Low Tire Warning light is on, check the air pressure in your tires as soon as possible, and inflate them to the recommended pressure. For more information about the TPMS Warning Light, Click Here For more information about the Tire Pressure Monitor System, Click Here. For more information about Tire Inflation Tips, Click Here.
LAMP OUT INDICATOR LIGHT This is a warning that you have a lamp out: a headlight, taillight, stop light or turn signal indicator. You can continue to drive your vehicle, but with reduced visibility and safety. Be warned that law enforcement officers may stop you and issue you a warning ticket or a safety violation ticket. Check all the lights on your vehicle when it is safe to do so (not in the middle of the highway at night!), and replace any bulbs that have burned out. In some cases, the problem might be a corroded or loose socket, loose or corroded wiring, or a blown fuse. For more information about lights, Click Here.
SEAT BELT LIGHT WARNING LIGHT OR CHIMES This little icon means somebody forgot to buckle up. Seat belts save lives so always use them, even on short trips. Driving without being bucked up may result in a ticket and a fine for a safety violation.
AIR BAG WARNING LIGHT A warning light that looks like this or says SRS should NEVER come on unless there is a fault in your vehicle's air bag system (supplemental restraint system or SRS). Like the engine computer and ABS computer, the air bag control module runs a self-check every time the vehicle is driven. If it finds a fault in a crash sensor, one of the air bag modules, the wiring or itself, it will set a code, turn on the warning light and disable itself. You can drive the vehicle but the air bag(s) will NOT deploy should you be involved in an accident. You should have the problem diagnosed and repaired at your earliest convenience. For more information about air bags, Click Here.
LOW WINDSHIELD WASHER FLUID WARNING LIGHT This is a reminder light that the fluid level is low in your windshield washer reservoir. Add fluid at your earliest convenience for safe driving. For more information about windshield wipers, Click Here.
DOOR AJAR WARNING LIGHT This is a reminder light that one of the doors (or tailgate) is not completely closed. Check all the doors (and tailgate) to make sure they are all latched properly. Sometimes the metal contacts that tell your vehicle the door is closed become dirty or corroded, causing a FALSE indication that a door is ajar. Cleaning the contacts will usually solve this kind of problem
SERVICE REMINDER LIGHT Many late model vehicles have an oil change reminder light that comes on when the engine computer estimates the oil needs to be changed. The calculations are based on hours of engine operation, vehicle speed, ambient temperatures and other http://www.aa1car.com/library/warning_lights.htm
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operating conditions. You do NOT have to change the oil immediately, but neither should you postpone the recommended maintenance too long. Oil should be changed every 3,000 miles for short trip city stop and go driving (especially during cold weather), or every 5,000 to 7,500 miles for mostly highway driving. Refer to your vehicle owners manual for the recommended service intervals. Many service reminder lights have a RESET button that allows you to turn off the light and reset the interval period. On some, though, a scan tool is required to turn off and reset the light. For more information about oil change intervals, Click Here.
MORE WARNING LIGHTS Many vehicles have their own unique warning lights or icons to alert you when something is wrong. You can usually find these in the back of your vehicle owners manual. Note: The appearance of some warning lights will vary depending on the country where the vehicle is sold. Below are some typical warning lights for a late model Lexus (courtesy Toyota):
Click to see larger image of warning lights.
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Related Articles: 5 Warning Lights You Should Never Ignore! Check Engine Light On Troubleshoot Check Engine Light Got a Trouble Code? Engine Oil Warning Light On Engine Temperature Warning Light On Engine Overheating Coolant Leak Car Won't Start (Possible Causes & Quick Checks) Troubleshoot Anti-Theft System Engine Won't Crank or Start Engine Won't Start, No Fuel (Bad Fuel Pump?) Engine Won't Start, No Spark
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Choosing A Scan Tool
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Scan Tool Diagnostics: Choosing a scan tool that's right for you Copyright AA1Car.com Adapted from an article written by Larry Carley for Import Car magazine
Buying a scan tool is easy, but figuring out which scan tool is the best one for you takes some research. You want a scan tool that will work on your vehicle (or the vehicles you service most often if your are a professional technician), is user friendly (easy to use menus) and is upgradeable. The tool also has to fit your budget. You cannot always get everything you want in a single scan tool. Some tools have more features than others. Some are slim, hand-held models and others are more bulky. Some can perform a wide range of tasks, while others can do only a few limited functions. Some require a major investment while others are relatively cheap. Finding the scan tool that is right for you is not easy because there are so many different ones from which to choose. There are basic code readers, pre-OBD II scan tools and OBD II-compliant scan tools. There are OEM scan tools and aftermarket scan tools. There are dedicated scan tools and software for converting laptop PCs and Palm Pilots into code readers and scan tools. How do you choose from such an array of products? ZEROING IN If you are a professional technician and specialize in a single import nameplate, for example, the OEM factory scan tool probably will be your best choice. Factory scan tools generally provide access to all the diagnostic trouble codes (both "generic OBD II" and "enhanced"), all the on-board test procedures, and usually most of the on-board electronics beyond engine performance and emissions (such as ABS, air bag, suspension and so on, if these systems have scan tool diagnostics).
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Unfortunately, OEM factory scan tools also are the most expensive and least flexible way to go. To make matters worse, some factory scan tools are essentially "dealer only" tools. The version they sell to the aftermarket may not be a full-featured unit and may lack some of the diagnostic tests or other capabilities that are included in the tool used by the new car dealer technicians. Some may not display all of the same PIDs (parameter identification) or data lines as the dealer tool. Others may do only engine performance and emissions, but not ABS, air bags or anything else. This situation is gradually improving as time goes on. For Honda and Accura applications, Teradyne (now out of business) made a Pocket PC platform that used the SAME software as the OEM Honda scan tool. For repair shops that specialize in a broader mix of import and/or domestic nameplates, buying a different OEM factory scan tool for each may be more than they can afford. Most factory scan tools sell in the $2,000-plus range, and they work on only a limited range of vehicle applications. Some OEMs have one scan tool for pre-OBD II vehicles and another for the newer OBD IIcompliant vehicles. For this kind of situation, an aftermarket scan tool such as those made by Actron, AutoXray, Equus, OTC, Snap-On and others might be a more affordable repair solution. But what kind of aftermarket scan tool? Aftermarket scan tools run the gamut from those for specific import makes (such as Volkswagen, Mercedes-Benz, etc.), to those that can interface with nearly all makes and models, both import and domestic. The "universal" scanners provide the most flexibility, but typically require purchasing additional cartridges and adapters to handle Asian and European makes. When you add up the cost of the scanner itself ($800 to $4,000 or more for a professional grade tool), plus the different cartridges and adapters, which may range in price from $300 to $800 or more, you can make a significant investment in diagnostic hardware and software, which also will have to be periodically updated with new software and/or hardware to keep up with changing technology. Keep in mind that every aftermarket scan tool is different. An $800 scanner will not have the same features and capabilities as one that costs five times as much. In some cases, you are paying extra for color graphics, a larger display or more built-in features, rather than add-ons, etc. So you have to shop and compare carefully to see exactly what you are getting. WHICH PLATFORM? In recent years, various vendors have developed software that allows an inexpensive Palm Pilot, Windows CE-based personal digital assistant (PDA), Pocket PC, tablet PC or even a smart cell phone to function as a scan tool. The sophistication of the software varies greatly as does its usefulness as a diagnostic tool. The simplest and cheapest packages that sell for a hundred dollars or less essentially give you the ability to plug a hand held device into the diagnostic connector on a 1996 or newer vehicle and use it as a code reader to display and clear generic OBD II fault codes. The better packages include enhanced codes for specific vehicle applications, and also may include the ability to display various PIDs such as sensor voltages, switch status and so on. The best software also includes graphics for displaying sensor voltages and other data. All of these devices require an interface cable or wireless connection to link the tool to the vehicle. In some cases, the software supplier provides the software at no charge but requires you to purchase the cable. The software, by itself, is useless without the cable or wireless connector to link the tool to your car. If you are resourceful and want to save a few bucks, there are numerous sources on the Internet where you can buy interface cables separately, or kits or plans to build your own cables. Software also is available that can convert a laptop or any other Windows-based PC into a scanner. Most require a Windows XP or higher operating system. Like the hand-held devices and smart phones, a laptop or PC also requires an interface cable or wireless connector to link your computer to your vehicle. One of the advantages of using a laptop or desktop PC as a scanner is the larger display. This makes it easier to read and list more information on a single screen. Most laptops have a screen that measures 12 to 17 inches diagonally, while most PC monitors range in size from 14 to 24 inches or larger. Another advantage of using a hand held device, smart phone, laptop or desktop PC as a scan tool is that it can easily be updated by downloading the latest software from the Internet. This also can be done with most dedicated scan tools using your PC for the download, and a USB cable or flash drive to transfer the update to the tool. On the other hand, dedicated scan tools are designed to be scanners and nothing else. You cannot surf the Internet with them or check your e-mail or auctions on eBay. But you can fix cars with them. Many professional-grade scan tools also include additional hardware circuitry and test leads that allow you to use the same tool as a multimeter to measure voltages,
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resistance and current. This is an extremely useful feature to have and eliminates the need for yet another piece of test equipment. Some of the more expensive scan tools also have the added ability to function as graphing multimeters or digital storage oscilloscopes. Being able to display sensor voltages as waveforms makes it much easier to detect problems that are nearly impossible to diagnose any other way. If you are looking for a multi-purpose tool that can be used as a scanner, multimeter and scope, choose one that can display more than one waveform at a time. Several units that are now on the market can simultaneously graph and display up to four different PIDs. DEPTH OF COVERAGE With import vehicles, coverage continues to be a major issue for some European makes. Until the arrival of OBD II, many imports lacked the ability to display sensor data or other diagnostic information through a scan tool. Many of the pre-OBD II Asian imports provide fault codes at the ECM with LEDs or have other flash codes so you do not need a scan tool for diagnostics. But on 1996 and newer vehicles, a scan tool has become mandatory. Some aftermarket universal scan tools and software packages provide good coverage on domestic and Asian makes, but only limited coverage on European makes. Others only read "generic" OBD II information on 1996 and newer import makes. One of the things to check out, therefore, when shopping for an aftermarket scan tool or scan tool software package is a list of what is covered, and what is not (which is much harder to obtain). Some claims can be misleading. A vendor may say their product or software package covers a long list of makes and models, but it may be only generic OBD II information. They may not even have enhanced codes for the applications listed. Others may provide all the OBD II codes but no additional codes for ABS, air bags or other systems beyond the engine and powertrain. Some may have limited diagnostics and not include all the factory tests or procedures. If you are not sure exactly what is or is not included, ask before you buy. MORE THAN ONE TOOL? Since it is obvious that one tool cannot do it all, many technicians buy more than one scanner and use different tools for different purposes. An inexpensive code reader can be used to read and clear most OBD II codes on 1996 and newer vehicles. This type of tool often can be used to make a quick diagnosis and, in many cases, you may not need anything else. But for advanced diagnostics, no-code fault diagnosis or any procedure that requires bidirectional communication with the vehicle computer, you need a professional grade scan tool or software package with advanced capabilities. One of the best software packages that is currently available checks all the sensor circuits and compares the values to knowngood values to flag potential problems. For some jobs, you also may need a tool that can graph or display waveforms. That means buying a digital storage oscilloscope if you do not buy a high-end scanner that can do both. Most scan tools display data stream values, which is what the PCM tells it to display. If the PCM is misreading a sensor input or is substituting bogus information, you have no way of knowing without actually testing the circuit or component in question. That is where a scope comes in handy. When a scope is hooked up to a sensor or circuit, it shows what is actually going on inside that device or circuit. Voltage is displayed as a time-based waveform. Once you know how to read waveforms, you can tell good ones from bad ones. You also can compare waveforms against scan tool data to see if the numbers agree (which is a great way to identify internal PCM faults). A scope also allows you to perform and verify "action-reaction" tests. You can use one channel to monitor the action or input, and a second, third or fourth channel to watch the results. For example, you might want to watch the throttle position sensor, fuel injector waveform, crank sensor signal and ignition pattern when blipping the throttle to catch an intermittent misfire condition. Using a scope does require a working knowledge of scope basics as well as the limitations of the scope you are using. Like scan tools, different scopes have different capabilities, so study and compare before you buy. ADDITIONAL REQUIREMENTS First and foremost is that you must Keep Your Scan Tool Up-To-Date. Software that is not current may not be able to display the latest trouble codes, complete PID lists or access onboard self-tests. Worse yet, out-of-date software may display
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incorrect or misleading results! So find check with your scan tool supplier to see how often they offer udpates. Something else to keep in mind is that a scan tool by itself cannot fix anything. It takes a brain to operate and use the information provided by the tool. That, in turn, requires an understanding of the vehicle systems you are working on, access to current service information, technical service bulletins and electrical wiring diagrams. If you do not know how the system works, what causes a code to set, or how a particular sensor or circuit is wired, how are you going to fix the fault? You also cannot rely on codes alone to identify all problems. Many problems never set a code. Some codes can be misleading because of the combination of circumstances that caused them to be set. Other codes may be false codes that never can be eliminated by normal repair procedures. You may have to reflash the computer to fix the problem. The best advice here is to always check for TSBs, whether you find any codes or not. In many instances, there will be a TSB that covers the problem and will save you hours of frustration. In conclusion, the more time and research you put into choosing a scan tool, the better satisfied you will be. Check with your equipment suppliers or the sources listed with this article for specific product models, features and prices. Spend some time on the Internet researching the various alternatives. Do your homework and you will find the tool (or tools) that are right for you.
Scan Tool Supplier Links: Actron Autel Auterra AutoBoss AutoEnginuity AutoLogic Baum Tools Bosch EASE Diagnostics Hanatech INNOVA/EQUUS Launch Lemur Monitors (Blue Driver OBD Scantool App) Nexiq OTC Ross-Tech Snap-On
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How to Diagnose a CAN Network
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How to Diagnose a Controller Area Network (CAN) Copyright AA1Car
Controller Area Network (CAN) electrical systems began to appear in new vehicles in 2003. Since then, more and more vehicles have been equipped with CAN systems, until 2008 when virtually all passenger cars and light trucks sold in the U.S. were CAN-equipped. As a vehicle owner or do-it-yourself mechanic, you need to know how CAN has made the electrical system in late model cars and trucks much more complicated than ever before. CAN allows various modules and systems to share data and interact in ways that where previously impossible. So what exactly is CAN? It is a communication standard that allows the various modules and computers in a vehicle to talk to one another via a common "data bus" circuit in the wiring system. Think of it as a high speed party line that allows data and commands to zip back and forth from one module to another. This allows the Powertrain Control Module (PCM), antilock brake/traction control/stability control system, electronic steering, electronic suspension, automatic climate control system, keyless entry system, lighting control modules and dozens of other systems and modules to all be interconnected electronically. The Development of Controller Area Networks for Cars CAN was created in 1984 by the Robert Bosch Corp. in anticipation of future advances in onboard electronics. The first production application was in 1992 on several Mercedes-Benz models. Today you will find it on all new vehicles.
Multi Protocol Analyzer A Monitor/Simulator of SPI, I2C, HDLC, CAN/LIN, FlexRay, USB, LAN
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How to Diagnose a CAN Network
CAN Diagnostics If you don't know the difference between a CAN data bus and a school bus, you're not alone. Even many professional mechanics are not yet up to speed on CAN diagnostics. Troubleshooting a late model CAN car is really no different than troubleshooting any late model OBD II vehicles. You need a scan tool to read out fault codes and other sensor data, and you need a scan tool that is CAN compliant. That means it has the proper software and hardware to communicate with the vehicle at higher speeds. Older scan tools (namely, most of those made before about 2006) lack the circuitry to talk to a CAN system. Some older scan tools have the right hardware, and can be upgraded with new software. But in most cases you will need a newer scan tool that is CAN-compliant to do onboard diagnostics. Most inexpensive scan tools designed for the DIY market are on-e-way tools: they can read codes and data, but they cannot send commands to the vehicle that are necessary to run all kinds of system self-tests. That degree of sophistication is reserved for more expensive professional level scan tools or factory scan tools. In addition, the software in a typical DIY scan tool (even if it is CAN-compliant) can usually only access powertrain codes. It can't talk to the ABS system, climate control system, electronic steering or suspension systems, climate control system, airbag system or other onboard electronics. In other words, it is a very limited tool. For advanced diagnositics that go beyond sijply reading powertrain fault codes and sensor data, you need a professional level tool or a factory tool. The latter can be quite expensive, costing thousands of dollars -- plus annual software updates that can add hundreds more. So if you need advanced diagnostics, the only option for most motorists and DIYers is to take your vehicle to a repair shop that has the proper diagnostic equipment.
How Information Moves Around Your Car in a CAN System Like many current vehicles, information in a CAN-equipped vehicle is shared over a serial data bus. The bus is the circuit that carries all the electronic chatter between modules (nodes). The bus may have one wire or two. If it has two, the wires are usually twisted to cancel out electromagnetic interference. The speed at which the bus carries information will vary depending on the "class" rating of the bus as well as the protocol to which it conforms. A data bus with a "Class A" speed rating is a relatively slow, low-speed circuit that typically carries less than 10 kilobits (10 Kbps) of information per second. A data bus that operates at Class A speeds is limited to simple command functions like operating power mirrors, power seats, power widows, power door locks, remote trunk releases and lights.
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A data bus with a "Class B" rating, by comparison, may operate from 10 Kbps up to 125 Kbps, depending on the operating protocol (SAE J1850 or Europe's ISO 9141-2). This is fast enough to carry more complex information and time-sensitive data. Systems that may may share a data bus with a Class B rating include electronic instrumentation, electronic transmission controls, security systems, and climate control. Class C is currently the fastest data bus rating. Class C systems can operate at speeds up to 1 megabits per second, which is up to 100 times faster than a typical Class B data bus. Many of the vehicles that are currently using a Class C data bus are operating at speeds of around 500 Kbps, which is fast enough for powertrain control modules, air bag modules, and fastacting antilock brake and stability control systems. Eeven faster CAN systems are coming with "class D" ratings of over 1 megabytes per second. And some applications such as onboard entertainment systems require even higher speed audio and video streaming. One thing to keep in mind about the CAN standard is that CAN as well as other protocols such as SAE J1939, GMLAN, OBD II, SAE J1587 and LIN have more to do with the way information is formatted, transmitted and received than how fast it is sent. This means the automotive engineers who design the onboard electronics for CAN-compliant vehicles are free to choose any operating speed they want (up to one megabits per second) as well as the type of bus conductor (one wire, twisted paired wires or a fiber optic cable). On most cars today, a high-speed data bus is needed to handle the volume of information going back and forth between all the onboard electronics. In 1995, GM introduced its own "Class 2" data bus to handle communication between modules. The system ran at a speed of 10,400 bits per second (10.4 Kbps), which was more than adequate for vehicles a decade ago. In 2004, GM moved to their next generation data bus system which they called "GMLAN" (GM Local Area Network). Introduced on the Cadillac XLR and Saturn Ion, GMLAN added the capability to operate at two speeds on two separate buses: a low speed (33.33 Kbps) bus and a high speed (500 Kbps) bus. The low speed side of the GMLAN system operates on a single wire bus to handle body-related control functions, while the high speed bus uses two wires to carry data between the powertrain, transmission and antilock brake modules. A "gateway" node connects the high speed bus and low speed bus, and allows information to be shared back and forth. For example, the radio (which is connected to the low speed bus) may adjust volume based on engine speed and vehicle speed (from the high speed bus) to offset road noise. Mercedes also uses several different bus speeds on their vehicles. Depending on the application, there may be a high-speed 500 Kbps CAN-C bus for the powertrain, transmission and ABS modules, and a slower-speed 83 Kbps CAN-B bus for the body control functions. On some Mercedes cars, there may be as many as 30 modules on the CAN-B bus. Up to model year 2002, all communication between the CAN-C and CAN-B bus went through the electronic ignition switch (EIS) module. After 2002, a new "gateway" module handles the inter-bus communications as well as onboard diagnostics via a CAN-D bus.
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How to Diagnose a CAN Network
How CAN Data is Sent and Received If your eyes haven't glazed over yet, here's how data is sent and received in a CAN system. Every module (node) that is attached to the data bus network is capable of sending and receiving signals. Each module (node) has its own unique address on the network. This allows the module to receive the inputs and data it needs to function, while ignoring information intended for other modules that share the network. When a module transmits information over the network, the information is coded so all the other modules recognize where it came from. Data is sent as a series of digital bits consisting of "0's" and "1's". If you looked at the data on a scope, you would see a square wave pattern that changes between a high and low voltage reading. The low voltage reading usually corresponds to the "0" while the high voltage reading corresponds to the "1". The actual voltage readings will vary depending on the application and protocols the vehicle manufacturer is using, but most operate in the 5 to 7 volts range. The CAN standard requires a "base frame" format for the data. What this means is that for each distinct message sent or received by a module on the network, there is a beginning bit (called the "start of frame" or "start of message" bit), followed by an "identifier" code (an 11 bit code that tells what kind of data the message contains), followed by a priority code ("remote transmission request") that says how important the data is, followed by 0 to 8 bytes (one byte equals 8 bits) of actual data, followed by some more bits that verify the information (cyclic redundancy check), followed by some end of message bits and an "end-of-frame" bit. Still with me? There's more! One of the tasks of any network system is to keep all the messages separated so they don't collide and garble one another. Usually the body control module or instrument cluster module is assigned the task of managing the network traffic. When it sees a message coming over the bus, it looks at the first bit in the data stream. If the bit is a "0", the message is given priority over the others. This is called a "dominant" message. If the first bit is a "1" it is given a lower priority (a "recessive" message). Thus, the highest priority messages always get through to their intended destinations but the low priority messages may be temporarily blocked until the traffic eases up.
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CAN System Faults CAN-compliant vehicles are just as vulnerable to electronic faults as older vehicles. Though CAN systems use fewer wires and fewer connectors to save weight and cost, they also use more modules and more complicated modules. Communication problems can occur if module connectors become corroded or loose, if wires become grounded, shorted or break, or system voltage is below specifications. Some modules may even forget their settings or locations if the battery is disconnected or goes dead. On some Chrysler minivans, for example, the automatic climate control system will quit working if battery power is lost. This happens because the electric stepper motors that control the position of the blend doors forget their locations. The system has to be put into a "relearn" mode to re-establish all the motor locations and settings. Various kinds of problems can occur on other CAN-equipped vehicles when the battery is disconnected or goes dead. The modules in the CAN system require a certain amount of voltage for their Keep Alive Memory settings. If this is lost, the module will forget these settings and may not function properly until it has time to relearn the lost data. In some cases, this requires a special relearn procedure using a scan tool because the module can't do the relearn by itself. And on some vehicles, the module may go to sleep and not wake up until it is pinged by a scan tool or the main gateway module (usually the body control module). Relearning procedures typically require a factory scan tool or a professional level aftermarket scan tool. One of the features of CAN and other network systems is that modules can send and receive "ok" signals to let the main control module know if they are working or not. In theory, this makes diagnostics easier. On the other hand, it also means that one misbehaving module may generate enough noise to disrupt the entire network causing a complete shutdown of the vehicle! When a serial bus communication problem occurs, it will usually set a "U" diagnostic trouble code (DTC) and turn on the Malfunction Indicator Lamp (MIL). Depending on the fault, the vehicle may or may not start, or it may only operate in a "limpin" mode with limited capabilities. Loss of communication between the engine controller and transmission controller (code U1026 on a GM, for example) may put the transmission into a limp-in mode where it will only operate in one or two gears. Loss of communication codes may indicate a wiring problem on the bus, or a fault with a module. Isolating the fault may require unplugging modules one at a time until the fault is found. Just remember that all modules on a bus network need three things to function properly: power, ground and a serial data connection.
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When diagnosing bus or module communication problems, you usually start by checking for voltage at the module, then the ground connection, and finally the data line. If all three are good but the module isn't working, the module needs to be replaced. On GM applications, a code U100 or U1255 means a general loss of communication on the data bus. With a Tech 2 scan tool, you can go to Diagnostic Circuit Check, then Message Monitor to see a list of active modules and compare it to the list of modules that are supposed to be on when the key is on. To minimize the parasitic current drain on the battery when the vehicle is off, a "sleep" signal is sent to the modules on the network. Some may remain on for a short period of time after the ignition is switched off (air bag module, for example), and some may never go to sleep (anti-theft module and keyless entry receiver, for example) but most are put into a sleep mode to save battery power. If the sleep signal is never sent, or a module fails to recognize the sleep signal, it may remain active and pull power from the battery. Depending on the current draw, this may run down the battery if the vehicle sits for a period of time.
CAN System Applications 2003 Ford Excursion, 2003 Ford F-250 & F-350, 2003 Ford Focus & Thunderbird, 2003 General Motors Saturn ION, 2003 Lincoln LS, 2003 Mazda 6, and 2003 SAAB 9-3 2004 Buick Rendezvous, 2004 Cadillac CTS, XLR & SRX, 2004 Dodge Durango, 2004 Ford Explorer, 2004 Ford F-150, E-250 & E-350, 2004 Ford Taurus, 2004 Lexus LS430, 2004 Mercury Mountaineer, 2004 Mercury Sable, 2004 Mazda 3 & RX-8, 2004 Toyota Prius, and 2004 Volvo S40 2005 Audi A4 & A6, 2005 Buick LaCrosse, Rendevous & Ranier, 2005 Cadillac STS, 2005 Chevrolet Cobalt, Corvette & Malibu, 2005 Chevrolet Equinox, 2005 Chevrolet SSR, 2005 Chevrolet Trailblazer EXT, 2005 Chrysler 300C, 2005 Dodge Dakota & Magnum, 2005 Ford Crown Victoria, Five Hundred, Focus & Mustang, 2005 Ford E-150, 2005 Ford Escape & Expedition, 2005 Ford Freestyle, 2005 GMC Envoy ESV & XL, 2005 Isuzu Ascender, 2005 Jeep Grand Cherokee, 2005 Lexus LS400 & GX470, 2005 Lincoln Town Car, 2005 Mercury Grand Marquis, Montigo & Sable, 2005 Mercury Mariner, 2005 Pontiac G6, Grand Prix & GTO, 2005 Land Rover LR3, 2005 Mazda MPV & Tribute, 2005 Mercedes SLK350, 2005 SAAB 97X, 2005 Toyota Avalon, 2005 Toyota 4Runner, Sequoia, Tacoma & Tundra, and 2005 Volvo S60, S80, V50, V70, XC90 Essentially ALL 2008 and newer model year passenger cars and light trucks.
CAN Code List Controller Area Network (CAN) generic OBD codes
Related Articles: CAN communication problem (what to do when the CAN system won't talk to your scan tool) Flash Reprogramming PCMs More on Flash Reprogramming PCMs Powertrain Control Modules (PCMs) Trouble Codes Making Sense of Engine Sensors Understanding Engine Management Systems Throttle-By-Wire systems (Electronic Throttle Control) All About Onboard Diagnostics II (OBD II) Zeroing in on OBD II Diagnostics
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CAN_communication_problem
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CAN Communication Problem Source: Illinois Air Team seminar instructor Ken Zanders
What to do if the CAN system on a 2004 or newer vehicle won't talk to your scan tool The first items you will need to verify are power and ground circuits for the DLC (Diagnostic Link Connector located under the instrument panel). You must first disable the vehicle so that it cranks but does not start. You will then perform a voltage drop check on the system ground. The use of a DLC breakout box (as shown below) is preferred for testing.
Attach one meter lead to Pin# 4 of the DLC and the other lead to battery negative with the engine cranking. Perform the same test on Pin# 5 of the DLC to battery negative as well. This is a good dynamic test that should show a voltage drop of .2 volts or less. The next test on the DLC will be to check Pin# 16 for battery voltage. You must always refer to service information to verify that you are testing the proper pins.
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The next step is to check communication circuits. There are terminating resistors that are used to reduce electrical noise on these communication circuits. A review of the schematics that refer to vehicle communication for the vehicle you are working on is a valuable asset to properly diagnosing a communication issue. It is strongly recommended that a DLC breakout box be used for testing. The first test procedure is to check between Pins# 6 and 14 of the DLC with an ohmmeter. This resistance check should yield a resistance value of approximately 60 ohms. An example system diagram is shown below for review.
The next test is to check voltage information on DLC pin# 6 and 14. Pin# 6 is normally denoted as CAN-H and Pin# 14 is normally denoted as CAN-L. The voltage information can be checked with a voltmeter or lab scope. If a voltmeter is used, it is important to note that a peak min-max function should be used with a time testing window of 1ms or less.
The voltmeter cannot tell you the quality of the signal being produced. A lab scope gives a visual picture of the electrical quality of the signal that is present. A sample CAN voltage pattern on a lab scope is shown below for reference.
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CAN H will have a voltage range of 2.5 to 3.5 volts, where as CAN L will have a range of 2.5 to 1.5 volts. The wiring on the vehicle must be checked for shorts to ground, voltage, or opens. If wires are next to each other, it is also possible for wires to be shorted to each other. In many cases, frayed wiring has contributed to lack of communication on many of the vehicles tested. It is also important to be able to attempt communication with the vehicle on the generic as well as the enhanced side. It is possible for it to communicate one way and not the other. When a vehicle is at the test facility, the communication attempt is made on the generic side. In closing, the breakout box provides a way to view the communication activity under dynamic conditions. You must always check all feeds, all grounds, and serial data to a module before any replacement is considered.
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Related Articles: Controller Area Network (CAN) Diagnostics Flash Reprogramming PCMs More on Flash Reprogramming PCMs Powertrain Control Modules (PCMs) Trouble Codes Making Sense of Engine Sensors Understanding Engine Management Systems Throttle-By-Wire systems (Electronic Throttle Control) All About Onboard Diagnostics II (OBD II) Zeroing in on OBD II Diagnostics
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OBD II Mode $06 Diagnostics
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OBD II Mode $06 Diagnostics Copyright AA1Car Mode $06 is an advanced diagnostic mode within the onboard diagnostic (OBD II) system on 1996 and newer vehicles that keeps watch on how all of the sensors and other emission control components are functioning. It can only be accessed with a professional grade scan tool, and requires scan tool software that can convert the hexadecimal (16-bit computer code) into ordinary numbers and values. In other words, it is an advanced diagnostic mode that can reveal the inner workings of the OBD II system, and can tell you when a code is going to set even before it sets the code and turns on the Check Engine light. An inexpensive code reader or basic scan tool can't access or read mode $06 data. Normally, most technicians ignore mode $06. On older scan tools, it was very difficult to access. And if they found it, the hexadecimal code looked like gibberish. You had to use conversion tables to translate the code into ordinary numbers, and you had to find the vehicle manufacturer's reference codes to decipher what each line meant. So it was a pain to use, and many technicians didn't even know it existed. As time went on, scan tool manufacturers began to add software to their tools that made Mode $06 easier to find a use. Many professional grade scan tools now display all of the mode $06 data in plain English with units of measure for various types of data (pressure, temperature, etc.). Some will even flag in red values that are out of range, making it much easier to spot problems that may set a code. The greatest value of mode $06 from a diagnostic standpoint is that it can verify repairs have fixed a problem without having to wait days for certain OBD II self-tests to run. To make sure a vehicle's emissions do not exceed federal limits, the OBD II system runs various self-checks (called "monitors") while the vehicle is being driven. Some of these monitors are "continuous" and monitor certain sensors and systems all the time. Other monitors (called "non-continuous" monitors) only run after certain operating conditions have been met. Consequently, non-continuous monitors may be slow to complete their self-checks, and may not set a fault code for several days or even weeks after a fault occurs. So being able to verify a repair has fixed a problem without having to wait for the Check Engine light to maybe come back on is a god way for repair shops to reduce comebacks and unhappy customers.
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OBD II Mode $06 Diagnostics
Mode $06 is most useful for checking misfires on Fords, and for checking the catalytic converter and evaporative emissions (EVAP) system on most cars. The latter two are non-continuous monitors and can be very slow to complete depending on driving conditions. Using Mode $06 to Diagnose Misfires Every time a cylinder misfires, OBD II adds one number to a running count of misfires for that cylinder. When the rate of misfire in any cylinder exceeds a certain threshold (typically around two percent), it will usually set a misfire code for that cylinder and turn on or flash the Check Engine light. If the misfire rate is less than about two percent, however, it usually will NOT set a code. Even so, the misfire may still be noticeable enough that you can feel it when the engine is under load or accelerating. By using your scan tool to access Mode $06 data, you can read the actual misfire counts that have been recorded for each cylinder. Note: This may require looking up the Mode $06 test reference code for the cylinder misfire data unless your scan tool translates that information for you. For example, on a Ford, the cylinder misfire data may be listed under TID $053. Each cylinder is identified as Component $01, $02, $03, etc., where the $ number corresponds to the cylinder number in the engine's firing order. Normally, the misfire count should be zero or very close to zero for each cylinder if there are no problems. If there have only been a few occasional misfires (say less than 100 over a given time period), that is usually acceptable. But if you see a relatively high count (say more than several hundred or a thousand misfires for a given cylinder), it would tell you the cylinder is experiencing an abnormal misfire rate and there is a problem with ignition, fuel or compression in that cylinder. For additional information on analyzing misfires, see the following: Misfire Analysis Misfire Diagnosis Misfires (causes of P0300 random misfire code) Misfire Diagnosis Chrysler 3.5L V6 Wells Mfg. has a good video on using Mode $06 to troubleshoot a misfire problem on a 2000 Ford Expedition. To watch the video, Click Here. How Mode $06 Data is Displayed On older professional grade scan tools, all of the mode $06 data is in hex code with no units of measure defined. On newer tools, the software will often translate the Mode $06 data into familiar terms and units of measure. The data is listed in three columns: * "TID" stands for Test identification. This is the sensor or component that is being monitored on that line. * "CID" stands for Component identification. This is the test result for that sensor or component. * PASS or FAIL in the last column indicates if the value is within range or out of range (less than the minimum acceptable value or greater than the maximum acceptable value for that sensor or component). Translating Mode $06 Hex Code If a scan tool does not translate the mode $06 hex code, tables that list the TID and CID definitions must be used to make sense of the data. Not all vehicle manufacturers publish their mode $06 information. Ford and GM's mode $06 information can be found on the vehicle manufacturer's service information websites, and on the International Automotive Technicians Network website (www.iatn.net). For GM Mode 06 charts, Click Here. For Honda or Acura Mode O6 charts, Click Here. Share
Additional Mode 06 Diagnostic Information: Mode $06 Diagnostic Update (a more recent article I wrote for Underhood Service magazine on this subject) D-Tips.com
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PCM Flash Reprogramming Procedures
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PCM Flash Reprogramming Procedure Copyright AA1Car Adapted from an article written by Larry Carley for Underhood Service magazine Flash reprogramming PCMs is NOT for the feint of heart. First, you have to have a scan tool or J2534 device that can reprogram your vehicle's computer. Then you have to go to the vehicle manufacturer's service information website, pay an access fee and find the correct update for your vehicle. Then you have to follow the exact procedure to download and install the update into your vehicle's computer. PCM flash reprogramming is becoming more and more necessary as vehicle modules get smarter and more complex. General Motors estimates that they have released flash updates for as many as 70% of 1995 and newer GM vehicles. PCM Programming is Nothing New Flash reprogrammable PCMs have been ussed in vehicles since the 1990s. The first such application was the 1990 Geo Storm. Previously, Program Read Only Memory (PROM) chips held all of the PCMs vital calibration information and operating instructions. GM pioneered the replaceable PROM chip as a way of programming PCMs to fit a wide range of GM makes and models. A replaceable PROM chip also meant the PCM could be "retuned" if necessary to correct certain kinds of emissions or driveability problems. It also meant that if a bug was later discovered in the original factory programming, it could be corrected in the field by simply replacing the original PROM with an updated corrected PROM (a tactic GM has successfully used over the years to fix many factory flaws). Performance enthusiasts also liked replaceable PROMs because the chip could be replaced with one that provided more spark advance, fuel enrichment, a higher rev limit, etc., to squeeze more power out of the engine. But replaceable PROMS had a serious drawback: there were too many of them! Every model year and every running change meant another PROM had to be created. Every field fix or recall for an emissions or driveability problem created more part numbers to keep track of. We are talking thousands of different PROMS. The General Motors PROM Identification manual that OTC used to provide with their Monitor scan tool and Pathfinder software contained more than 362 pages of GM PROM numbers! Enter the flash reprogrammable EEPROM (Electronically Erasable Program Read Only Memory) chip. PCMs built with EEPROM chips can be reprogrammed in a matter of minutes without having to remove the PCM or replace a single chip. It is all done digitally with the proper access codes and input data. Following the Geo Storm, GM began phasing in PCMs with flash reprogrammable chips in a variety of cars and trucks. By 1995, most GM models had the flash reprogrammable PCMs. Ford and Chrysler were also doing the same thing as OBD II arrived on all cars and light trucks in model year 1996. Today, virtually all PCMs have reprogramming capabilities as do many
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other onboard control modules (ABS, air bags, climate control, body controller, etc.). This allows changes and upgrades to be made as needed.
Why Reprogram PCM?
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PCMs may need to be reprogrammed for several reasons. One is to fix factory bugs. Every time Bill Gates rushes yet another version of Windows to market to perpetuate the Microsoft revenue stream, it always turns out to have bugs and security holes that were somehow missed but must be fixed by downloading and installing the latest Windows "service pack." It's a never-ending cycle of upgrades and patches. Fortunately, it is not that bad yet with automotive PCMs, but it has become a crutch for automakers who rush products to market that aren't quite ready. This philosophy of "build it now and fix it later" creates a lot of unnecessary recalls, but at least it gives technicians a way to fix factory mistakes without having to replace any parts.
A reflash may also be required if the factory settings for the OBD II selfdiagnostics turn out to be overly sensitive - especially after a few years of operation. The same goes for driveability. What works fine in a brand new car many not work so great after 50,000 or 100,000 miles of realworld driving. Changing the fuel enrichment curve, spark timing or some emissions control function slightly may be necessary to eliminate a hesitation, spark knock or other condition that develops over time. For example, on certain GM vehicles the Check Engine light comes on and sets a code P1406 that indicates a fault in the position of the exhaust gas recirculation (EGR) valve. Cleaning or replacing the EGR valve and clearing the code does not fix the vehicle because the code usually returns. The real problem is the OBD II programming in the PCM. When the PCM commands the EGR valve to open to check its operation, it isn't allowing enough time for the valve to respond. A brand new valve takes only about 50 milliseconds to open but an older valve may take up to 350 milliseconds or longer - which is not long enough to cause a real NOx emissions failure but is long enough to trip a fault code. The fix in this instance is to reflash the PCM with new instructions that allow more time for the EGR valve to respond. Another example are rich codes that may appear on some late-model GM vehicles. The problem here is that the original OBD II self-diagnostic programming does not allow enough leeway for changes in intake vacuum that occur as the engine ages. After 60,000 miles, intake vacuum isn't as high as in a new engine, which can create a rich fuel condition. The cure is to flash reprogram the PCM to compensate for the drop in vacuum. When vehicle manufacturers calibrate the onboard diagnostics to meet federal emissions standards, they have to draw the line somewhere as to what operating conditions might cause emissions to exceed federal limits 1.5 times. That is the threshold where a fault code must be set and the Check Engine light must come on. It doesn't mean emissions really are over the limit, but it is possible based on laboratory dyno testing and field experience. Depending on the application, the vehicle manufacturer may even set the limit a little lower just to be safe because the last thing any OEM wants is an expensive emissions recall. The best advice when confronted with a troublesome code that keeps coming back or seems to set for no apparent reason is to check for any technical service bulletins that may have been published. Chances are it might be a programming issue that requires a reflash to fix. Something else to keep in mind with respect to many late-model flash reprogrammable PCMs: if you replace the PCM for any reason, the replacement unit may have to be reflashed before it will start the engine! Some modules are plug-and-play, and are preprogrammed by the dealer or aftermarket parts supplier so they can be installed ready-to-go. But many need vehicle specific calibration information to run properly. This may require downloading old calibration information from the original PCM (if possible) and reloading it into the replacement PCM, or getting updated calibration information from the vehicle manufacturer to install in the new module. If you are buying a reman PCM from an aftermarket supplier, they may be able to program it for you. The information they need to do this includes your year, make and model of vehicle, engine size, vehicle identification number (VIN), the type of transmission (manual or automatic), the emissions type (federal certification or California), and other options that may affect the calibration of the PCM. Your other option is to have a car dealer or repair shop reflash the computer, or attempt it yourself.
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Historically, car dealers have been the only ones who had access to the tools and software needed to reflash PCMs. Thanks to the passing of Senate Bill 1146 in September 2000, vehicle manufacturers must now make this technology available to independent repair shops and individuals at reasonable cost. Starting in 2004, flash reprogramming procedures also had to conform to SAE J2534 standards that allow the use of aftermarket scan tools or similar pass-through devices. Reflashing PCMs requires three things: a scan tool or J2534 pass-through device that is flash capable, a Windows desktop or laptop computer with an internet connection for downloading the flash software from the vehicle manufacturer website (Click Here for a list of OEM Service Websites & Access Fees), and a subscription to the manufacturer's database so you can access the software or get the software updates on CDs. Other items that are needed include a cable to connect the PC to the scan tool or J2534 pass-through device, and a cable to connect the scan tool or J2534 pass-through device to the OBD II connector on the vehicle. For GM applications, you need a Tech 2 scan tool or Vetronix Mastertech. For Ford applications, you need a Ford New Generation Star (NGS) scan tool, or their new IDS scan tool. For Chrysler applications, you need a Diagnostic and Reprogramming Tool (DART) or a Chrysler DRB III scan tool. These tools are available from OTC Div of SPX Corp. To view or download a copy of the DART users manual, Click Here (The manual is a PDF file). Generic reprogramming tools can also be used to reflash Chrysler PCMs, but Chrysler says they have encountered some problems with certain J2534 devices. This involves all their powertrain SCI engine computers from 1996 to 2004, and some PCMs from 2005. To avoid such problems, Chrysler recommends using the CTC Vehicle Box J2534 (http://www.ctchome.com/vehiclebox.html) device while performing SCI protocol-based reprogramming using their J2534 flash application. Before you begin a reflash on a Chrysler PCM, the programming application needs to establish successful communication with the vehicle computer. This can be accomplished by doing the following steps: Temporarily disconnect all aftermarket alarms, remote start systems, audio systems to prevent electronic interference. Check vehicle wiring for any obvious defects. Use the recommended J2534 device. For technicians using a factory service tool, Chrysler's wiTECH is capable of programming SCI computers in 2004 and newer vehicles. For 2003 and older vehicles, the DRB III scan tool should be used. For import applications, you need whatever factory scan tool the dealer uses, an aftermarket scan tool with reflash capabilities for that vehicle, or a J2534 pass-through device that will work on the vehicle. Yearly and monthly access fees to OEM databases tend to be very pricey, but one-day or short-term access fees are typically available for $20 to $25. Some vehicle manufacturers provide their flash updates on a CD once you pay their subscription fee. Others provide the software update as a download over the internet after you pay their fee. The download goes into your desktop or laptop computer. In some cases, the software must then be copied to a flash card which is then plugged into a scan tool or J2534 device for installation into the vehicle. In other cases, the software is fed through a cable or wireless connection to the J2534 device so it can be installed in the vehicle. NOTE> If the software download is feeding through an internet connection into the J2534 tool as it is being installed, you have to maintain the internet connection without interruption until the installation has been completed. If you lose the internet connection, you will have to start the installation all over again -- and hopefully it will work. Losing the connection part way through an installation may royally screw up the PCM! The flash procedure can takes from a few minutes up to an hour depending on the file size of the software you are installing. The newer and more complex the vehicle, the longer it typically takes to flash the PCM. GM Flash Updates On GM vehicles, a list of flash updates that are available can be found on GM's Vehicle PCM Calibration Information website at https://tis2web.service.gm.com/tis2web. The actual reprogramming procedure for a typical GM vehicle goes as follows: 1. Check the calibration history of the vehicle -- Go to the GM web page at https://tis2web.service.gm.com/tis2web to
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see what the latest vehicle calibration is for your car by entering the vehicle VIN number. If the PCM programming has been updated, the most recent calibration will be listed on the website. You can't download the new calibration software from the website,however. You must first purchase a TIS subscription from GM, and then GM will mail you the calibration software on a CD. The software can then be copied from the CD through your PC to a flash card for the Tech 2 scan tool. 2. Connect your PC to the Tech 2 scan tool with a RS232 cable pass-through device. 3. Before you start the procedure, make sure the battery is fully charged. You do NOT want any loss of voltage during the procedure as this can really screw things up! GM does NOT approve using a battery charger, unless it is a GMapproved Midtronics charger (which delivers very consistent voltage with no fluctuations). On some vehicles, removing the fuses for the fan relays, fuel pump or other modules may be required to prevent these devices from turning on during the procedure. 4. Start the GM recalibration software program on your PC (which you have to purchase from GM, along with the update CDs) and enter the vehicle application information (year, make, model, etc.). 5. Connect the Tech 2 scan tool to the diagnostic connector on the vehicle (located under the dash near the steering column). 6. Switch the Tech 2 scan tool on and wait for the Start screen. 7. Validate the vehicle VIN number. 8. Choose the operating system, engine, fuel system, speedometer or transmission. 9. Select "normal reprogramming" or "VCI" (special modifications). 10. Choose the update bulletin/recalibration number from the menu. 11. Start the transfer of data. As the software is loaded, you will see a progress bar. The reprogramming procedure may take a new minutes to 30 minutes or more depending on the file size, and can be done with the computer in or out of the vehicle. The PC screen will display a blue progress bar as the software is uploading to the vehicle. Note: The GM setup will NOT allow the same calibration to be reinstalled over itself. Only an updated calibration can be loaded into the vehicle computer. There is no going back to an earlier version. 12. When the software has finished loading, the message "PROGRAMMING COMPLETE" will appear. 13. Turn the ignition OFF, then disconnect the scan tool. Depending on the application, it may be necessary to run one or more "relearn" procedures before the PCM will function properly. Most GM PCMs require a "CASE" relearn so the PCM can learn the relative positions between the crankshaft and camshaft sensors. If you don't do the CASE relearn, the Check Engine Light will come on and there will be a code P1336. Ford Flash Procedure With Ford vehicles, a somewhat different approach is used. First, you need the vehicle calibration ID number. This can be found on a sticker somewhere in the engine compartment. Next, you have to figure out if there is a newer calibration available. This requires going to the www.motorcraftservice.com website, selecting "Quick Guides" on the left side of the screen. On the next menu page that appears, scroll down to the link for "Latest Calibration Information." The next screen says "Search Calibration by Vehicle, Model Year and Engine." Enter your vehicle model, year and engine information, and click Submit. The next screen will list all of the possible calibrations by PCM part number. Find the part number that matches your PCM and that's the latest calibration you need. To get the actual calibration download, click on the "Reprogramming & Initialization" link at the left. You then have to buy a one-day subscription before you can download the software to your PC that is necessary to do the reflash. You will also need a J-2534 pass thru tool to do the reflash. With Ford, the calibration software that will go into the car is not stored on the PC. The software that you downloaded only facilitates the transfer of the new calibration from Ford into the car. In other words, it is a "live" procedure that requires a continuous unbroken internet connection until it has finished.
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PCM Flash Reprogramming Procedures
Chrysler Flash Procedure Chrysler's flash procedure is sort of a cross between GM and Ford's procedures. First you go to the www.techauthority.com website and download their "benchtop Programmer" software to your PC. Then you download a huge pdf file ("J2534 Flash Availability") that lists all Chrysler PCMs and their software updates. Chrysler uses vehicle body codes to identify the PCM in addition to the VIN, and you need to use a scan tool to get the module ID from the vehicle. If the vehicle needs a update, you go back to the Chrysler website, pay their access fee, and download the new software to your PC. Then you transfer the software from the PC to a scan tool or J-2534 pass-through tool to install it in the vehicle. Also note, many Chrysler PCMs require a re-initialization procedure after a flash. For more information about this, click here (requires Adobe Acrobat to open pdf file). Here is a sample of the flash reprogram procedure a Chrysler dealer would use. This one happens to be for a recall Chrysler issued for 1999 California Dodge Ram Pickups and Vans with 5.9L engine ("Z" engine code in the 8th VIN position), automatic transmission and California emissions control system (code NAE). The OBD II catalyst monitor on these vehicles may not detect a catalyst failure so the PCM programming had to be revised to comply with California regulations. The dealer accesses the latest software through the modem connection in the Mopar Diagnostic System, and feeds it through the DRB III scan tool into the vehicle's PCM via the OBD II connector. The process begins by turning the ignition key on (engine off) and allowing the scan tool to "auto connect" with the PCM. Once the lines of communication are open, the VIN is displayed on the scan tool. The technician can now press the "OK" button to proceed with the reflash procedure. The first thing he does is select "Read Part Numbers From Vehicle" and click "Show Updates" on the MDS2. If somebody has already reflashed the PCM, the screen will say "Part number is up to date and does not require any new updates." The software number should be compared to the latest version to verify the numbers match just the same. If the PCM has not yet been updated, the technician clicks OK, selects the new software part number and clicks "Update Controller Software." From that point on, the process is automatic - but there is a hitch. During the flash reprogramming procedure, the PCM loses communication with other modules on the vehicle that may set a number of "false" trouble codes for the transmission module, ABS module, body control module, etc. This does not indicate a problem and the codes can be erased after the flash reprogramming procedure has been completed. The technician is also supposed to attach a label to the PCM with the reflash part number and date indicating the PCM has been reflashed. WARNING! PCM Flashing Is Not Without Risk So what happens if something goes wrong during a reflash procedure? Anyone who has ever experienced a crash while installing new software on a PC knows it can cause real problems. In some cases, the PCM may be so scrambled that it will not accept a reflash, which means you get to buy a new PCM! Chrysler issued a TSB (18-32-98) that deals with how to recover from a flash reprogramming failure. The bulletin says, "Occasionally a flash update procedure may not complete properly and/or the diagnostic equipment may lock up during the procedure." Common causes of flash errors include poor cable connections between the PC, scan tool and vehicle, loss of power to the diagnostic equipment while the flash procedure is underway, turning off the vehicle ignition switch before the flash procedure is complete, unfamiliarity with the procedure (pushing the wrong buttons), or low vehicle battery voltage. If the process crashes, recheck all the cable connections to assure good communications and reinitialize the flash procedure. In other words, if at first you don't succeed, try, try again. On the Chrysler applications, you may also have to identify which type of controller is on the vehicle (SBEC2, SBEC3, JTEC 96-98, JTEC+ 99, etc.) to get the system to accept the new programming. If you get an error message again, you probably selected the wrong controller type (try again!). Doing your own flash reprogramming is not without risk. Any number of things can go wrong during the installation process which may result in an incomplete update or a frozen PCM. The worst case is that you can't recover the PCM and have to replace it. Out advice is to leave PCM updates to a knowledgeable professional. If your vehicle needs a flash update, take it to the car dealer or a qualified repair shop and let them do the update.
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How to Reprogram PCM
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Reprogram PCM Copyright AA1Car Car companies are relying more and more on flash reprogramming to correct driveability and emissions related problems in newer vehicles. This procedure is usually done at a new car dealership, but with the right software and tools independent repair shops or even individuals can reprogram their PCM Powertrain Control Modules (PCMs) and other onboard electronics. U.S. Environmental Protection Agency regulations require original equipment manufacturers to make emissions-related onboard diagnostic service information available to the aftermarket via their technical websites, including updates on reprogramming vehicle modules. The flash reprogramming procedures must conform to SAE J-2534-1 standards, which allow the use of aftermarket scan tools or similar pass-through devices in addition to the factory scan tool. EPA rules require auto makers to post all of their text-based service and training information on the internet so anyone can access it, and at reasonable cost. For a complete listing of these websites and fees, Click Here. MOST LATE MODEL VEHICLES CAN BE FLASH REPROGRAMMED Most domestic vehicles built since 1996 (over 150 million!) have computers that can be reprogrammed (for a listing of vehicles that can be flash reprogrammed, Click Here). Reprogramming may be required for a variety of reasons. One is when a vehicle sets false trouble codes. The original factory programing may be overly sensitive or not take into account wear or other factors that may affect the operation of certain sensors or the OBD II monitors. CLICK HERE for a list of General Motors modules that are reprogrammable on 1993 to 2008 model year vehicles (pdf file). PCM Reprogramming is also necessary to change the engine idle speed, spark timing, fuel mixture or other emission control functions. PCM Reprogramming may be required to resolve a hot or cold starting issue, idle roughness, stalling, or an emissions failure. Reprogramming is often used to modify the operation of emission functions so they have less of an effect on drivability.
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How to Reprogram PCM
PCM Reprogramming may be necessary to smooth out or change the shift characteristics of an automatic transmission. It may also be used to modify the operation of the ABS, traction control or stability control systems, to change steering feel on vehicles with variable assist steering, and to change the ride characteristics on vehicles with electronic ride control. If a PCM, TCM, BCM or other control module is being replaced on a vehicle, reprogramming may be required to calibrate the new module to that particular vehicle (unless it has been preflashed by the OEM or module supplier). Also, additional learning procedures may be required to "initialize" the module so it will function properly. One thing reprogramming cannot do is fix mechanical problems like vacuum leaks, dirty fuel injectors, worn spark plugs, piston rings or bearings. If an engine or other component has a mechanical problem, these need to be diagnosed and ruled out or repaired before reprogramming is considered as a repair possibility. PERFORMANCE REPROGRAMMING A PCM Reprogramming is also a trick that many tuners use to enhance engine performance and dial-in more horsepower. Reprogramming can change spark timing, fuel enrichment and boost pressure (on turbocharged and supercharged engines) to make more power. Reprogramming is usually required after installing an aftermarket performance cam, bigger cylinder heads, a different intake manifold or fuel induction system to compensate for changes in airflow. Many performance chips on the market claim to remap engine timing by altering sensor readings sent to the ECU, but a professional tune is still highly recommended for these chips as well, when used in conjunction with other aftermarket parts. Reprogramming can also change the shift points of the transmission, disable the factory built-in rev limiter and vehicle speed limiter, and recalibrate the ABS/traction control system for different sized aftermarket tires and wheels. This type of reprogramming, however, requires a special aftermarket tuner scan tool, as well as software that is not provided (or approved) by the vehicle manufacturer. HOW A PCM STORES PROGRAMMING INFORMATION Before Onboard Diagnostics II arrived in 1996, the calibration instructions for most PCMs and other modules were located on "Program Read Only Memory" (PROM) chips. These integrated circuit chips were plugged into the module main circuit board, and could only be programmed once. If the instructions needed to be changed or updated for any reason, the PROM chip had to be physically removed from the module and replaced with a newer version. This created a proliferation of OEM PROM part numbers, as well as a lot of confusion about which PROM was the "right" one for a particular application, as well as which PROM was the latest version. For performance tuning, the original PROM chip could be replaced with an aftermarket performance PROM chip that provided more spark advance and fuel enrichment under certain driving conditions. But on vehicles that lacked a PROM chip, this was not possible. Caution: PROM chip can be easily damaged by mishandling. Static electricity can zap the chip's memory, and the little prongs that plugged into the circuit board can be easily bent or broken. If you are replacing a PROM chip, you should wear an anti-static wrist ground strap and take precautions to minimize the risk of a static discharge. In the early 1990s, General Motors began to use a new type of memory chip called an EPROM (Erasable Program Read Only Memory). This chip had a little window on it that allowed the chip to be reprogrammed with new instructions when it was exposed to a bright ultraviolet (UV) lamp. As the technology continued to evolve, the next improvement was the EEPROM (Electronically Erasable Program Read Only Memory) chip. These started to appear on OBD II cars in 1996, and soon became common because EEPROM chips could be electronically reprogrammed without having to remove the chip or expose it to an ultraviolet lamp. It could be reprogrammed by applying a higher than normal voltage. This told the chip to accept new instructions so new information could overwrite the old information on the chip. The latest version of this technology is the Flash EEPROM, which is essentially a higher capacity EEPROM chip that can hold more information (typically 512 megabytes or more) and can be overwritten more quickly and easily. TOOLS REQUIRED TO REPROGRAM PCM To reprogram a PCM or other vehicle module, you need a factory scan tool, or an aftermarket scan tool with reprogramming capabilities, or a J-2534 compliant "PassThru" interface tool (or J-2534-1 for 2004 & newer vehicles) that can connect a PC or scan tool to the vehicle's diagnostic connector or module. The updated software for reprogramming the vehicle comes from the vehicle manufacturer. The software may be downloaded from their website (which requires a broadband, DSL or faster connection, not a simple dial-up connection), or it may be supplied via CD or DVD after paying their subscription fee. With few exceptions, the software is NOT free. A subscription fee or access fee must be paid to obtain the software. And to install it, you need a scan tool with reprogramming capability, or a
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J-2534 or J-2534-1 PassThru tool. For a list of subscription fees and OEM technical websites for accessing this information, see Listing of OEM websites and fees. HOW TO REPROGRAM A PCM OR OTHER MODULE The first step is to determine whether or not any updates are available for a particular vehicle, and if so whether or not such an update might be needed to solve a particular problem. Updates can be found by searching recent TSBs or recalls. This will tell you which makes/models/years (or VINs or module part numbers) are covered by an update, and what symptom, problem or issue the update is designed to resolve. NOTE: Even though an update may be available for a vehicle, it does NOT mean the vehicle must be updated. As long as the vehicle is running fine and is experiencing no problems, there is no need to update it. On the other hand, if the vehicle has a problem that may be resolved by installing an update, then updating would be a good idea. The next step is to use a scan tool to determine which version of software is currently loaded in the vehicle. If it is not the latest version, and the vehicle is having a problem (or would benefit from an upgrade), reprogramming would be the next step. After downloading or obtaining the latest software from the OEM, the information must be transferred to a scan tool or J-2534 PassThru device that is plugged into the vehicle diagnostic connector. Modules can also be bench reprogrammed off the vehicle by connecting the scan tool or PassThru tool directly to the module, but it is usually easier to reprogram it on the vehicle. Caution: During the reprogramming procedure, power to the module and reprogramming tool must not be interrupted. A charger should be attached to the battery to make sure there is a steady supply of voltage during the procedure. Also, the scan tool or J-2534 PassThru tool must not be disconnected until after the installation is complete. Warning: On some older GM class 2 PCMs, if anything goes wrong during the reprogramming procedure, it may not be possible to undo the damage. The module may not accept any further information and may have to be replaced! IMPORTANT: Reprogramming is not reversible. Once the latest version of software has been installed, you can't go back to the old version. Nor can you install the same version of software over itself. GM FLASH UPDATES On GM vehicles, a list of flash updates that are available can be found on GM's Vehicle PCM Calibration Information website at https://tis2web.service.gm.com/tis2web (note, there is no www before the web address on this site). All that's needed to update a GM computer is a Tech 2 scan tool, the special OEM software from GM (which must be obtained from a GM dealer or their technical website) and a passthru tool that allows the update to be downloaded from the internet or a CD or DVD and loaded through the scan tool into the vehicle's computer. The actual reprogramming procedure for a GM vehicle goes as follows: 1. Check the calibration history of the vehicle -- Go to the GM web page at https://tis2web.service.gm.com/tis2web and see what latest program is for the vehicle using the vehicle's VIN number. If the programming has been updated to correct a problem, it will be listed on the website 2. Connect your PC to the Tech 2 scan tool with a RS232 cable pass-thru device. 3. Start the GM recalibration software program on your PC and enter the vehicle application information (year, make, model, etc.). 4. Connect the Tech 2 scan tool to the diagnostic connector on the vehicle (located under the dash near the steering column). 5. Switch the Tech 2 scan tool on and wait for the Start Screen. 6. Validate the vehicle VIN number. 7. Choose the operating system, engine, fuel system, speedometer or transmission. 8. Select "normal reprogramming" or "VCI" (special modifications).
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9. Choose the update bulletin/recalibration number from the menu. 10. Start the transfer of data. The reprogramming procedure takes about three minutes, and can be done with the computer in or out of the vehicle. The PC screen will display a blue progress bar as the software is uploading to the vehicle. NOTE: The GM setup will not allow the same calibration to be reinstalled over itself. Only an updated calibration can be loaded into the vehicle computer. 11. When the software has finished loading, the message "PROGRAMMING COMPLETE" will appear. 12. The scan tool can now be disconnected from the vehicle (turn ignition off first), and any subsequent relearning procedures that may be needed such as the crankshaft position variation relearn procedure can now be performed to finish the update.
Update: September 2014
New J-2534 Programming Specification Addresses Flash Programming Issues The new SAE J2534-1 v 05.00 specification addresses issues of incompatibility of some J-device flash reprogramming tools with current vehicle applications. The latest specification more closely defines reprogramming criteria to reduce ambiguity that can lead to flash programming issues on some applications. The new SAE J2534-3 Compliance Tests will assure that scan tools and vehicles meet these criteria so vehicle PCMs can be flash reprogrammed with fewer problems. The new spec also allows ISO 15765 CAN to have multiple 'Logical' channels and adds support for full and half-duplex functionality that can facilitate much faster reprogramming times. Unfortunately, the new J2534-1 specification is not backward compatible. Because of this, current J-devices must have software/firmware updates and OEM applications will need to be edited or rewritten to comply with the new 05.00 version of SAE J2534-1. According to a report by the National Automotive Service Task Force (NASTF), the California Air Resources Board (CARB) does not appear to be in a hurry to require OEMs implement this new spec. Some OEMs may voluntarily write new application software, but considering the expense and pending upgrades due for all model-year 2018 vehicles, the OEMs may be slow in the rollout.
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More Engine Computer Related Articles: PCM Flash Reprogramming Procedures Powertrain Control Modules (PCMs) General Motors Reprogrammable Module List 2003-2008 (pdf file) Scan Tool Companion software Scan Tool Help Scan Tools (how to buy) Tuner Scan Tools Onboard Diagnostics II (OBD II) OBD II Diagnostics OBD II Driveability & Emissions Problems CAN communication problem (what to do when the CAN system won't talk to your scan tool)
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Powertrain Control Module (PCM)
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Home, Automotive Repair Library, Auto Parts, Accessories, Tools & Equipment, Manuals & Books, Car BLOG, Links, Index Got a Powertrain Control Module Problem? Need Help Now? Click the Banner Below to Ask an Expert:
Powertrain Control Module (PCM) Copyright AA1Car Fred Foster
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... The onboard computer, or Powertrain Control Module (PCM),is the brains of the engine control system, so when the brain is not functioning correctly neither is the engine or anything else that the microprocessor controls - which may include the charging system, transmission, various emission controls and communications with other onboard control modules. Once a diagnosis has been made (and we emphasize the word diagnosis), then and only then should the PCM be replaced. Onboard Diagnostic (OBD II) diagnostic trouble codes that typically indicate a fault with the powertrain control module include: P0600....Serial Communication Link P0601....Internal Control Module Memory Check Sum Error P0602....Control Module Programming Error P0603....Internal Control Module Keep Alive Memory (KAM) Error
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P0604....Internal Control Module Random Access Memory (RAM) Error P0605....Internal Control Module Read Only Memory (ROM) Error P0606....ECM/PCM Processor P0607....Control Module Performance P0608....Control Module VSS Output 'A'
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Powertrain Control Module (PCM)
P0609....Control Module VSS Output 'B' P0610....Control Module Vehicle Options Error If you see any of these codes when diagnosing the vehicle with a code reader or scan tool, it may mean the PCM has failed and must be replaced. Additional diagnostic tests will usually be necessary to confirm the problem is really the powertrain control module and NOT something else. Refer to the OEM diagnostic charts for what these tests are. Usually it involves checking certain inputs to the PCM to see if it outputs the correct response. No response or an incorrect response usually means the PCM is defective and needs to be replaced. All too often, technicians tend to blame that which they understand least. If an engine is not running right and the cause is not obvious, they may blame the computer. Throwing parts at a problem in an attempt to solve it may be good for the parts business, but when a customer brings a PCM back because it failed to fix their problem, nobody wins. Warranty returns on complicated and expensive components like powertrain control modules are an ongoing problem that costs everyone money. UNNECESSARY POWERTRAIN CONTROL MODULE RETURNS. Over 50 percent of PCMs that are returned under warranty (either because the PCM failed to fix a performance problem or because the engine did not run properly after it was installed) have nothing wrong with them! So it is obvious a lot of people are swapping computers to see if a different PCM will fix their problem. The trouble with returns is if the PCM has been on the car, you have no way of knowing if it is still "good" or not. Somebody may have crossed up some wires, zapped the PCM with too much voltage or who knows what? The computer needs to be tested and verified before it can go back on the shelf and be sold to somebody else. Unfortunately, there is no easy way of doing that in a parts store. The PCM has to be hooked up to a sophisticated simulator that exercises all of the computer's input and output circuits to make sure it works correctly - which means the PCM has to go back to the supplier, be retested, and if no fault is found, repackaged and put back into stock. Be warned, though, that many parts stores have a policy of "no returns or refunds on electronic components." WHY DID THE POWERTRAIN CONTROL MODULE DIE? One way to reduce the risk of PCM warranty problems is to find out why the old PCM died. Determining the cause of death may not always be possible, but it may be essential to prevent the same thing from damaging the replacement PCM in some cases. PCMs typically fail for one of two reasons: voltage overloads (often due to a short in a solenoid or actuator circuit) or environmental factors (corrosion, thermal stress or vibration). If the shorted solenoid or actuator is not found and repaired, the voltage overload it creates may damage the replacement PCM, too. As for environmental factors, water is the main thing to avoid. If water gets inside a PCM, it can short circuits and set up irreversible corrosion that ruins electronic connections. Most remanufacturers will not even attempt to repair a PCM if the vehicle it came out of was submerged in a flood. Replacement is the only option. Thermal stress and vibration can form microcracks in circuit boards (which are repairable). This often has more to due with the ruggedness of the circuit design than operation factors in the vehicle itself. ACCURATE POWERTRAIN CONTROL MODULE IDENTIFICATION Because there are so many different PCMs, accurate identification of the PCM and its correct replacement is absolutely essential to prevent unnecessary returns. Many PCMs appear to be exactly the same on the outside (same sized box and connectors) but may be wired or calibrated differently inside. If the wrong PCM is installed in a vehicle, it may run but probably will not run well. Close enough is not good enough when it comes to replacing PCMs. It must be the correct replacement for the application. Accurately identifying the PCM requires not only the vehicle year, make, model and engine size, but also the OEM part number on the PCM itself. Most supplier catalogs list replacement PCMs both ways. So if in doubt, always refer to the OEM number on the PCM and look it up in the suppliers cross reference index to find their replacement part number. The calibration chip and PROM contains the programming instructions for the vehicle application. That is why it usually does not come with the replacement PCM. There are too many different possibilities. On many newer vehicles, flash memory or "EEPROMs" (Electronically Erasable Program Read Only Memory) are used. If the replacement PROM is not properly
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programmed for the application, it must be reprogrammed after it has been installed. Unfortunately, the ability to do this type of reprogramming is not readily available to the aftermarket. The car makers do not want aftermarket technicians messing around with the calibration of their onboard computers because they are afraid doing so may alter emissions or performance. But that is another issue. One such example is Chrysler transmission modules. They must be reset with the factory DRB scan tool and dealer codes to set the "pinion factor," which controls the operation of the speedometer. REMAN POWERTRAIN CONTROL MODULES Because a powertrain control module can be very expensive to replace, almost all aftermarket replacement PCMs are "remanufactured" units. A PCM is not rebuilt in the same way that an alternator or water pump is rebuilt because there are no mechanical parts that wear out. Remanufacturing in this case usually means testing the powertrain control module, isolating and repairing any faults that may be found, then retesting the powert5ain control module to make sure everything works correctly. A remanufactured PCM is typically sold one of two ways: on an exchange basis from stock, or on a custom rebuild basis. If a particular PCM is not in stock or is unavailable, you may be able to send an old PCM to a remanufacturer for repair. Turn around time is typically a few days and the cost is about the same as an exchange unit except there is no core charge). The hard part is finding a remanufacturer who can test and repair your powertrain control module. Some PCMs, though, may not be repairable. As we said earlier, most remanufacturers will not even touch a PCM if it came out of a flooded vehicle. PCM REPLACEMENT TIPS
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Replacing a PCM is essentially a matter of swapping boxes. Accessibility can be a problem on some vehicles because the PCM is often buried under or behind other components in the instrument panel, climate control system or console. Some are located under a seat and require removing the seat. Regardless of the PCM's location, though, one thing you should do prior to removing the old PCM and installing the replacement PCM is disconnect the battery. Once the PCM has been installed and reconnected, the battery can be reconnected, too. But the job is not done yet. Many PCMs have to undergo a "relearning" procedure after they have been installed or if they have been disconnected from the battery. On some newer vehicles, a scan tool may be required to reprogram the PCM and to reset the anti-theft system.
On some applications, there may be a specific relearn procedure for establishing the base idle speed and other operating parameters. On others, it may be necessary to take the vehicle for a short test drive so the computer can adjust itself. The exact requirements will be spelled out in the vehicle service manual. The best advice here is to test drive the vehicle after the powertrain control module has been installed. A short drive cycle that includes going over 35 mph will usually reset most PCMs so they will operate properly. The powertrain control module will also continue to learn and make small adjustments to the fuel mixture and other functions over time as the vehicle accumulates miles. If the PCM also controls the transmission, it may take awhile to relearn the driver's habits so the transmission may not shift exactly the same as before until this occurs. Finally, if the Malfunction Indicator Lamp (MIL) or Check Engine light comes back on after the PCM has been replaced, it means there is still a problem with the vehicle. The fault is probably NOT the PCM, unless the fault code is for an internal PCM fault. The presence of fault codes means additional diagnosis is required to identify and repair the fault. And until the real problem is found and fixed, the PCM may not function normally. If the engine control system is not going into closed loop, chances are the coolant sensor or oxygen sensor may not be working properly. If spark timing seems to be over advanced or retarded, the problem may be a faulty MAP sensor, misadjusted throttle position sensor or overly sensitive knock sensor. And if nothing seems to work right, low charging voltage due to a weak alternator or poor battery connections may be the fault. http://www.aa1car.com/library/pcm.htm
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Remember, a powertrain control module needs all its sensor inputs, proper battery voltage, a good ground and the ability to send out control signals to function normally.
Powertrain Control Module Resources: Blue Streak Electronics PCM Relearn Tips page Standard Motor PCM Relearn Tech Tips (PDF file)
PCM Related Articles: Toyota Recalls 2005 to 2008 Corolla & Matrix for Defective Engine Computer Flash Reprogramming PCMs More on Flash Reprogramming PCMs Powertrain Control Module Performance Tuning Module Madness (TechShop magazine offsite link) Trouble Codes Making Sense of Engine Sensors Understanding Oxygen (O2) Sensors Wide Ratio Air Fuel (WRAF) Sensors Air Temperature Sensors Coolant Sensors Crankshaft Position CKP Sensors MAP sensors Mass Airflow MAF Sensors Vane Airflow VAF Sensors Throttle Position Sensors Understanding Engine Management Systems All About Onboard Diagnostics II (OBD II) OBD II Diagnostic Tips Zeroing in on OBD II Diagnostics Controller Area Network (CAN) Diagnostics
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Computer Engine Controls Copyright AA1Car Adapted from an article written by Larry Carley for Counterman magazine The performance and emissions that today's engines deliver would be impossible without the electronics that control everything from ignition and fuel delivery to every aspect of emissions. Electronics make possible V8 engines that deliver excellent performance, good fuel economy and produce almost no pollution. But there's a price to be paid for today's technology, and that price is complexity. Many Powertrain Control Modules (PCMs) today have 16-bit and even 32-bit processors. Though not as powerful as the latest desktop personal computers, PCMs can still crunch a lot of information. It's been said that today's automotive PCMs have more computing power than the Space Shuttle's main processors. Kind of scary to think about, isn't it? So, does it take a rocket scientist to troubleshoot and repair drivability problems in today's cars? No, but it does take a lot of knowledge, experience and sophisticated diagnostic equipment. Fortunately, you don't have to be an expert to replace engine management parts if you know something about the basics of computerized engine control, what the sensors do and how to diagnose common faults. INSIDE THE PCM From the outside, most PCMs look similar: just a metal box with some connectors on it. The PCM's job is to manage the powertrain. This includes the engine's ignition system, fuel injection system and emission controls. The PCM receives inputs from a wide variety of sensors and switches. Some of the more important ones will be discussed in the following paragraphs. ENGINE CONTROL SYSTEM SENSORS The oxygen sensor provides information about the fuel mixture. The PCM uses this to constantly re-adjust and fine tune the air/fuel ratio. This keeps emissions and fuel consumption to a minimum. A bad O2 sensor will typically make an engine run rich, use more fuel and pollute. O2 sensors tend to deteriorate with age and may be contaminated if the engine burns oil or develops a coolant leak.
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On 1996 and newer vehicles, there is also an additional O2 sensor behind the catalytic converter to monitor converter efficiency. Though most O2 sensors have no recommended replacement interval (replace "as needed" only), sluggish O2 sensors can be replaced to restore like-new performance. Unheated one- or two-wire O2 sensors on 1976 through early 1990s applications can be replaced every 30,000 to 50,000 miles. Heated three- and four-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 miles. And on OBD II equipped vehicles, the sensor could be replaced once it has seen 100,000 miles. The coolant sensor monitors engine temperature. The PCM uses this information to regulate a wide variety of ignition, fuel and emission control functions. When the engine is cold, for example, the fuel mixture needs to be richer to improve drivability. Once the engine reaches a certain temperature, the PCM starts using the signal from the O2 sensor to vary the fuel mixture. This is called "closed loop" operation, and it is necessary to keep emissions to a minimum. The throttle position sensor (TPS) keeps the PCM informed about throttle position. The PCM uses this input to change spark timing and the fuel mixture as engine load changes. A problem here can cause a flat spot during acceleration (like a bad accelerator pump in a carburetor) as well as other drivability complaints. The Airflow Sensor, of which there are several types(Mass Air Flow (MAF) sensor or a Vane Air Flow (VAF) sensor), tells the PCM how much air the engine is drawing in as it runs. The PCM uses this to further vary the fuel mixture as needed. There are several types of airflow sensors including hot wire mass airflow sensors and the older flap-style vane airflow sensors. All are very expensive to replace. Some engines do not have an airflow sensor and only estimate how much air the engine is actually taking in by monitoring engine rpm and using inputs from the throttle position sensor, a manifold absolute pressure (MAP) sensor and manifold air temperature (MAT) sensor. Problems with the airflow sensor can upset the fuel mixture and various drivability problems (hard starting, hesitation, stalling, rough idle, etc.) The crankshaft position sensor serves the same function as the pickup assembly in an engine with a distributor. It does two things: It monitors engine rpm and helps the computer determine relative position of the crankshaft so the PCM can control spark timing and fuel delivery in the proper sequence. The PCM also uses the crank sensor's input to regulate idle speed, which it does by sending a signal to an idle speed control motor or idle air bypass motor. On some engines, an additional camshaft position sensor is used to provide additional input to the PCM about valve timing. The manifold absolute pressure (MAP) sensor measures intake vacuum, which the PCM also uses to determine engine load. The MAP sensor's input affects ignition timing primarily, but also fuel delivery. Knock sensors are used to detect vibrations produced by detonation. When the PCM receives a signal from the knock sensor, it momentarily retards timing while the engine is under load to protect the engine against spark knock. The EGR position sensor tells the PCM when the exhaust gas recirculation (EGR) valve opens (and how much). This allows the PCM to detect problems with the EGR system that would increase pollution. The vehicle speed sensor (VSS) keeps the PCM informed about how fast the vehicle is traveling. This is needed to control other functions such as torque converter lockup. The VSS signal is also used by other control modules, including the antilock brake system (ABS). A couple of things to keep in mind when replacing sensors: Parts that are physically interchangeable may not be calibrated the same and won't work properly if installed in the wrong application. To make sure you get the correct replacement part, it may be necessary to refer to the vehicle VIN as well as OEM numbers on the original part. Some aftermarket parts may not look exactly the same as the original. A "universal" O2 sensor, for example, may fit a large number of applications but usually requires cutting and splicing wires to install. OTHER PCM FUNCTIONS On many vehicles the PCM also controls the transmission. But on some vehicles, a separate transmission control module (TCM) is used to oversee gear changes and the torque converter. But even if there's a separate module for the transmission, the PCM and TCM talk to each other and share data so each knows what the other is doing. On many newer vehicles, the PCM also regulates charging system voltage; cycles the cooling fan on and off; interacts with the antilock brake system (ABS) module to reduce power if the vehicle has traction control; and may even interact with the automatic temperature control (ATC) module to operate the cycling of the air conditioning compressor clutch. The PCM may also be assigned vehicle security tasks. One of the PCM's most important jobs is to make sure all the engine's sensors are working properly and that the engine isn't
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polluting. Since the earliest days of the onboard computer, a certain amount of self-diagnostic capability has always been required to detect problems that might upset the smooth operation of the system. If a fault is detected, the PCM will set a trouble code. On older vehicles, the diagnostics for the engine control system were relatively crude. If a sensor circuit went open (no signal) or shorted, the gross failure would set a trouble code and turn on the check engine light. But many conditions that didn't cause a total failure could also upset engine performance and drivability. What's more, the earlier systems had no way of monitoring many conditions that could increase pollution. So the Environmental Protection Agency (EPA) required every city and state that didn't meet Federal clean air standards to institute some type of vehicle emissions inspection program. EMISSIONS AND OBD II Emissions testing has certainly helped boost the sales of aftermarket PCMs, sensors and emission control parts. But more importantly, it has made a significant improvement in the air quality of most large metropolitan areas. Even so, many motorists will only seek repairs if forced to do so because their vehicle failed an emissions test. Many put off repairs until their vehicle is barely drivable or dies and leaves them stranded. With computerized engine control systems, it doesn't take much of a sensor input problem to adversely affect driveability and emissions. A sluggish O2 sensor, a defective coolant sensor that always stays cold, a throttle position sensor that has a dead spot, an airflow sensor that isn't reading accurately, etc., can all hurt performance, fuel economy and emissions. In an attempt to ratchet up the self-diagnostic capability of PCMs, the California Air Resources Board developed a "next generation" onboard diagnostic system called OBD II. "OBD" is an acronym for "On Board Diagnostics." The "2" stands for "second-generation system." OBD II first appeared in 1994, and it has been required on all cars and light trucks since 1996. Unlike earlier onboard diagnostic systems that set a diagnostic trouble code only when a sensor failed or read out of range, OBD II monitors most engine functions while the vehicle is being driven. It is designed to detect almost any problem that can cause emissions to exceed the federal limit by 1.5 times. OBD II is extremely sensitive. Some say it is overly sensitive because the vehicle manufacturers have been overly cautious in setting trigger points below the 1.5 threshold to reduce the risk of expensive emission recalls. As a result, some vehicles may not actually have an emissions problem when the Check Engine light is on. Nevertheless, the problem should always be investigated to determine the cause.
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CHECK ENGINE LIGHT The Check Engine Light (Malfunction Indicator Lamp or MIL) is supposed to alert the driver when an emissions or sensor problem occurs. Depending on how the system is configured and the nature of the problem, the lamp may come on and go off, remain on continuously or flash - all of which can be very confusing because you have no way of knowing what the light means. Is it a serious problem or not? If the engine seems to be running okay, should you ignore the light or not? To address this issue, AutoZone recently announced a nationwide "Check Engine Light Program" for its stores. When a motorist has a Check Engine light on, he can take his vehicle to an AutoZone store for a free diagnosis. A store employee plugs a code reader or basic scan tool into the vehicle's diagnostic connector and reads out the code. In theory, this provides a diagnosis so the appropriate part(s) can be replaced. Unfortunately, it's not as simple as it sounds. A trouble code is only a starting place. It's not the final diagnosis. Somebody still has to check out the various components in the affected circuit to determine exactly what is causing the problem. This often requires following a lengthy diagnostic chart to isolate the fault. Jumping to conclusions often results in a faulty diagnosis. For example, let's say a vehicle has an OBD II code for the oxygen sensor circuit (code P0130). The code might indicate a bad sensor, or it might indicate a loose connector or wiring problem. Harder to diagnose are misfire codes. OBD II can detect misfires in individual cylinders as well as random misfires. If it generates a misfire code for a single cylinder (say P0301 for the #1 cylinder), it only tells you the cylinder is misfiring - not why. The underlying cause could be a bad spark plug, a bad plug wire, a weak coil on a distributorless ignition system (DIS) or coil-on-plug (COP) ignition system, a dirty or dead fuel injector or a compression problem (bad valve, leaky head gasket, rounded cam lobe, etc.). As you can see, there are multiple possibilities, so it takes some diagnostic expertise to isolate the fault before any parts can be replaced. A random misfire code (P0300) is even harder to diagnose because there can be numerous causes. A random misfire usually means the air/fuel mixture is running lean. But the cause might be anything from a hard-to-find vacuum leak to dirty injectors, low fuel pressure, a weak ignition coil, bad plug wires or compression problems. Something else to keep in mind about OBD II fault codes is that some codes are false codes. GM has had problems with certain 3.8L engines setting P1406 codes, which indicates a fault in the EGR valve. Replacing the EGR valve doesn't fix the problem because the OBD II system is overly sensitive to how quickly the EGR valve opens when it is commanded to do so by the PCM. The cure here is not to replace the EGR valve but to "flash reprogram" the computer so it is less sensitive to this condition. Referring to vehicle manufacturer technical service bulletins (TSBs) can save a lot of time and frustration for these kinds of problems. Something else that complicates diagnosis is that "standardized" OBD II codes really aren't. There are actually two different types. "Generic" OBD II codes are the same in the sense that all vehicle manufacturers use the same code numbers to indicate the same type of problem. But each vehicle manufacturer also has their own special "enhanced" codes that cover problems not included in the basic OBD II code list. These include many problems not covered by the generic codes as well as problems that are outside the engine management system such as ABS codes, climate control codes, body codes, air bag codes, etc. Generic OBD II codes all start with "P0" while the OEM enhanced codes all start with a "P1." Enhanced codes are often
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vehicle specific and may not be readable with some code readers or scan tools. In other words, it may require special software or a dealer scan tool to read the enhanced codes. Diagnosing computerized engine control systems and sensors isn't an easy task, but that's the price we pay for drastically reduced emissions and the feature-laden vehicles we drive today. So make sure your customers have done their diagnostic homework before they replace critical engine management system parts. It will save you both a lot of frustration and needless returns. ENGINE SENSOR REPLACEMENT A couple of things to keep in mind when selling replacement sensors: Parts that are physically interchangeable may not be calibrated the same and won't work properly if installed in the wrong application. To make sure your customer gets the correct replacement part, it may be necessary to refer to the vehicle VIN as well as OEM numbers on the original part. Some aftermarket parts may not look exactly the same as the original. A "universal" O2 sensor, for example, may fit a large number of applications but usually requires cutting and splicing wires to install. OXYGEN SENSOR REPLACEMENT INTERVALS Though most O2 sensors have no recommended replacement interval (replace "as needed" only), sluggish O2 sensors can be replaced to restore like-new performance. Unheated one- or two-wire O2 sensors on 1976 through early 1990s applications can be replaced every 30,000 to 50,000 miles. Heated three- and four-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 to 80,000 miles. And on OBD II equipped vehicles, the sensor can be replaced once it has seen 100,000 miles or more to restore like-new performance.
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Related Articles: Toyota Recalls 2005 to 2008 Corolla & Matrix for Defective Engine Computer Making Sense of Engine Sensors Air Temperature Sensors Coolant Sensors Crankshaft Position CKP Sensors Understanding Oxygen (O2) Sensors Wide Ratio Air Fuel (WRAF) Sensors Sensing Emission Problems (O2 Sensors) MAP sensors Mass Airflow MAF Sensors Vane Airflow VAF Sensors Throttle Position Sensors Powertrain control modules (PCMs) All About Onboard Diagnostics II (OBD II) TROUBLE CODES Help Diagnosic Tips for Trouble Codes
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Making Sense of Engine Sensors Copyright AA1Car Computers can only do what they are programmed to do. If they get garbage in, they put garbage out. In an automotive engine control computer (called a Powertrain Control Module or PCM), the input data is not from a keyboard but electronic signals from various sensors. They act the like the engines eyes and ears helping it make the most of its driving conditions. Consequently, the Powertrain Control Module (PCM) can't do this if the inputs it receives are faulty or missing. For example, the engine control system will not go into "closed loop," if the PCM does not receive a good signal from the coolant sensor or oxygen sensor. Nor can it balance the fuel mixture correctly if it does not receive good inputs from the throttle position sensor, MAP sensor or airflow sensor. The engine may not even start if the PCM does not get a signal from the crankshaft position sensor. Sensors monitor all the key functions necessary to manage ignition timing, fuel delivery, emission controls, transmission shifting, cruise control, engine torque reduction (if the vehicle has antilock brakes with traction control) and charging output of the alternator. On many late model vehicles (Toyota, Nissan, etc.), the PCM even controls the throttle because there is no direct cable or linkage connection to the throttle. Reliable sensor inputs are an absolute must if the whole system is to operate smoothly.
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COOLANT SENSOR
Usually located on the cylinder head or intake manifold, the coolant sensor is used to monitor the temperature of the engine coolant. Its resistance changes in proportion to coolant temperature. Input from the coolant sensor tells the computer when the engine is warm so the PCM can go into closed loop feedback fuel control and handle other emission functions (EGR, canister purge, etc.) that may be temperature dependent. Coolant Sensor Strategies: The coolant sensor is a pretty reliable sensor, but if it fails it can prevent the engine control system from going into closed loop. This will result in a rich fuel mixture, excessive fuel consumption and elevated carbon monoxide (CO) emissions - which may cause the vehicle to fail an emissions test. A bad sensor can be diagnosed by measuring its resistance and watching for a change as the engine warms up. No change, or an open or closed reading would indicate a bad sensor. OXYGEN (O2) SENSOR
Used on both carbureted and fuel injected engines since 1981, the oxygen (O2) sensor is the key sensor in the fuel mixture feedback control loop. Mounted in the exhaust manifold, the O2 sensor monitors the amount of unburned oxygen in the exhaust. On many V6 and V8 engines, there are two such sensors (one for each bank of cylinders). The O2 sensor generates a voltage signal that is proportional to the amount of unburned oxygen in the exhaust. When the fuel mixture is rich, most of the oxygen is consumed during combustion so there is little unburned oxygen in the exhaust. The difference in oxygen levels between the exhaust inside the manifold and the air outside creates an electrical potential across the sensors platinum and zirconium tip. This causes the sensor to generate a voltage signal. The sensor's output is high (up to 0.9v) when the fuel mixture is rich (low oxygen), and low (down to 0.1v) when the mixture is lean (high oxygen). Sensor output is monitored by the computer and is used to rebalance the fuel mixture for lowest emissions. When the sensor reads "lean" the PCM increases the on-time of the injectors to make the fuel mixture go rich. Conversely, when the http://www.aa1car.com/library/1999/cm69910.htm
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sensor reads "rich" the PCM shortens the on-time of the injectors to make the fuel mixture go lean. This causes a rapid back-and-forth switching from rich to lean and back again as the engine is running. These even waves result in an "average" mixture that is almost perfectly balanced for clean combustion. The switching rate is slowest in older feedback carburetors, faster is throttle body injection systems and fastest in multiport sequential fuel injection. If the O2 sensor's output is monitored on an oscilloscope, it will produce a zigzagging line that dances back and forth from rich to lean. Think of it as a kind of heart monitor for the engine's air/fuel mixture. O2 Sensor Strategies: Unheated one- or two-wire O2 sensors on 1976 through early 1990s applications should be replaced every 30,000 to 50,000 miles to assure reliable performance. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications should be changed every 60,000 miles. On OBD II equipped vehicles, the recommended replacement interval is 100,000 miles. The O2 sensor's responsiveness and voltage output can diminish with age and exposure to certain contaminants in the exhaust such as lead, sulfur, silicone (coolant leaks) and phosphorus (oil burning). If the sensor becomes contaminated, it may not respond very quickly to changes in the air/fuel mixture causing a lag in the PCMs ability to control the air/fuel mixture. The sensor's voltage output may decline giving a lower than normal reading. This may cause the PCM to react as if the fuel mixture were leaner than it really is resulting in an overly rich fuel mixture. How common is this problem? One EPA study found that 70 percent of the vehicles that failed an I/M 240 emissions test needed a new O2 sensor.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor is mounted on or connected to the intake manifold to monitor intake vacuum. It changes voltage or frequency as manifold pressure changes. The computer uses this information to measure engine load so ignition timing can be advanced and retarded as needed. It performs essentially the same job as the vacuum advance diaphragm on an old fashioned mechanical distributor. On engines with a "speed density" type of fuel injection, the MAP sensor also helps the PCM estimate airflow. Problems here may cause an intermittent check engine light (light comes on when accelerating or when the engine is under load), hesitation when accelerating, elevated emissions and poor engine performance. The engine will run with a bad MAP sensor, but it will run poorly. Some PCMs can substitute "estimated data" for a missing or out of range MAP signal, but engine performance will be drastically reduced. MAP Sensor Strategies: Some MAP sensor problems are not the fault of the sensor itself. If the vacuum hose that connects the MAP sensor to the intake manifold is loose, leaking or plugged, the sensor cannot produce an accurate signal. Also, if there is a problem within the engine itself that causes intake vacuum to be lower than normal (such as a vacuum leak, EGR valve that is stuck open or leaky PCV hose), the MAP sensor's readings may be lower than normal. THROTTLE POSITION SENSOR
Mounted on the throttle shaft of the carburetor or throttle body, the throttle position Sensor (TPS) changes resistance as the throttle opens and closes. The computer uses this information to monitor engine load, acceleration, deceleration and when http://www.aa1car.com/library/1999/cm69910.htm
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the engine is at idle or wide open throttle. The sensor's signal is used by the PCM to enrich the fuel mixture during acceleration, and to retard and advance ignition timing. Throttle Position Sensor Strategies: Many TPS sensors require an initial voltage adjustment when installed. This adjustment is critical for accurate operation. On some engines, a separate idle switch and/or wide open throttle (WOT) switch may also be used. Driveability symptoms due to a bad TPS can be similar to those caused by a bad MAP sensor: The engine will run without this input, but it will run poorly. MASS AIRFLOW SENSOR (MAF)
Mounted ahead of the throttle body on multiport fuel injected engines, the MAF sensor monitors the volume of air entering the engine. The sensor uses either a hot wire or heated filament to measure both airflow and air density. MAF Sensor Strategies: The sensing element in MAF sensors can be easily contaminated causing hard starting, rough idle, hesitation and stalling problems. Cleaning a dirty MAF sensor with electronics cleaner can often restore normal sensor operation and save the cost of having to replace the sensor (which is very expensive!). VANE AIRFLOW SENSOR (VAF)
The VAF sensor has a mechanical flap-style sensor that is used on Bosch and other import multiport fuel injected engines. The function is the same as a mass airflow sensor, but air pushing against a spring-loaded flap moves a rheostat to generate an electronic signal. VAF Sensor Strategies: The drivability symptoms for the VAF are the same as those of a mass airflow sensor if the sensor fails. MANIFOLD AIR TEMPERATURE (MAT) SENSOR
Mounted on the intake manifold, this sensor changes resistance to monitor incoming air temperature. The sensor's input is used to adjust the fuel mixture for changes in air density. MAT Sensor Strategies: Problems with the manifold air temp sensor can affect the air/fuel mixture, causing the engine to run rich or lean. CRANKSHAFT POSITION SENSOR
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Used on engines with distributorless ignition systems, the crankshaft position (CKP) sensor serves essentially the same purpose as the ignition pickup and trigger wheel in an electronic distributor. It generates a signal that the PCM needs to determine the position of the crankshaft and the number one cylinder. This information is necessary to control ignition timing and the operation of the fuel injectors. The signal from the crank sensor also tells the PCM how fast the engine is running (engine rpm) so ignition timing can be advanced or retarded as needed. On some engines, a separate camshaft position sensor is also used to help the PCM determine the correct firing order. The engine will not run without this sensor's input. There are two basic types of crankshaft position sensors: magnetic and Hall effect. The magnetic type uses a magnet to sense notches in the crankshaft or harmonic balancer. As the notch passes underneath, it causes a change in the magnetic field that produces an alternating current signal. The frequency of the signal gives the PCM the information it needs to control timing. The Hall effect type of crank sensor uses notches or shutter blades on the crank, cam gear or balancer to disrupt a magnetic field in the Hall effect sensor window. This causes the sensor to switch on and off, producing a digital signal that the PCM reads to determine crank position and speed. Crank Position Sensor Strategies: If a crank position sensor fails, the engine will die. The engine may, however, still crank but it will not start. Most problems can be traced to faults in the sensor wiring harness. A disruption of the sensor supply voltage (Hall effect types), ground or return circuits can cause a loss of the all-important timing signal. KNOCK SENSOR
The knock sensor detects engine vibrations that indicate detonation is occurring so the computer can momentarily retard timing. Some engines have two knock sensors. Knock Sensor Strategies: A failure with the knock sensor can cause spark knock and engine damaging detonation because the PCM will not know to retard ignition timing if knock is occurring. BAROMETRIC PRESSURE (BARO) SENSOR
The baro sensor measures barometric pressure so the computer can compensate for changes in altitude and/or barometric pressure that would affect the fuel mixture or timing. Some MAP sensors also perform this function. VEHICLE SPEED SENSOR (VSS)
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The vehicle speed sensor, or VSS, monitors vehicle speed so the computer can regulate torque converter clutch lockup, shifting, etc. The sensor may be located on the transmission, differential, transaxle or speedometer head. Vehicle Speed Sensor Strategies: A problem with the vehicle speed sensor can disable the cruise-control system as well as affect transmission shifting and converter engagement. MAKING SENSE OF IT ALL If you have not done your diagnostic homework and are replacing a sensor because you think it might be bad, you may be wasting money. Replacing a sensor won't solve a drivability or emissions problem if the problem is not the sensor. Common conditions such as fouled spark plugs, bad plug wires, a weak ignition coil, a leaky EGR valve, vacuum leaks, low compression, dirty injectors, low fuel pressure or even low charging voltage can all cause driveability symptoms that may be blamed on a bad sensor. If there are no sensor-specific fault codes, these kinds of possibilities should be ruled out before much time is spent on electronic diagnosis.
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Engine Air Temperature Sensor
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Engine Air Temperature Sensor Copyright AA1Car The Intake Air Temperature sensor (IAT) monitors the temperature of the air entering the engine. The engine computer (PCM) needs this information to estimate air density so it can balance air air/fuel mixture. Colder air is more dense than hot air, so cold air requires more fuel to maintain the same air/fuel ratio. The PCM changes the air/fuel ratio by changing the length (on time) of the injector pulses. On pre-OBD II vehicles (1995 & older), this sensor may be called an Air Charge Temperature (ACT) sensor, a Vane Air Temperature (VAT) sensor, a Manifold Charging Temperature (MCT) sensor, a Manifold Air Temperature (MAT) sensor or a Charge Temperature Sensor (CTS). HOW THE AIR TEMPERATURE SENSOR WORKS The Intake Air Temperature sensor is usually mounted in the intake manifold so the tip will be exposed to air entering the engine. On engines that use mass airflow (MAF) sensors to monitor the volume of air entering the engine, the MAP sensor will also have an air temperature sensor built into it. Some engines may also have more than one air temperature sensor (two if it has a split intake manifold or separate intake manifolds on a V6 or V8 engine).
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The air temperature sensor is a thermistor, which means its electrical resistance changes in response to changes in temperature. It works the same as a coolant sensor. The PCM applies a reference voltage to the sensor (usually 5 volts), then looks at the voltage signal it receives back to calculate air temperature. The return voltage signal will change in proportion to changes in air temperature. Most air temperature sensors are negative temperature coefficient (NTC) thermistors with high electrical resistance when they are cold, but the resistance drops as they heat up. However, some work in the opposite manner. They are positive temperature coefficient (PTC) thermistors that have low resistance when cold, and increase in resistance as they heat up. The changing resistance of the sensor causes a change in the return voltage back to the PCM. On older pre-OBD II applications (1995 & older vehicles), the signal from the air temperature sensor may also be used to turn on the cold start injector (if used) if the outside air temperature is cold. On some of these older applications, the air temperature sensor signal may also be used to delay the opening of the EGR valve until the engine warms up. Air temperature sensors are also used in Automatic Climate Control systems. One or more air temperature sensors are used to monitor the temperature of the air inside the passenger compartment, as well as the outside air temperature. The climate control system usually has its own separate outside air temperature sensor located outside the engine compartment so engine heat does not affect it. The outside air temperature sensor will usually be mounted behind the grille or in the cowl area at the base of the windshield.). Most of these sensors work exactly the same as the engine air temperature sensor. But some use an infrared sensor to monitor the body temperature of the vehicle’s occupants. CAUSES OF FAILURE An air temperature sensor can sometimes be damaged by backfiring in the intake manifold. Carbon and oil contamination inside the intake manifold can also coat the tip of the sensor, making it less responsive to sudden changes in air temperature. The air temperature sensor itself may also degrade as a result of heat or old age, causing it to respond more slowly or not at all. Sensor problems can also be caused by poor electrical connections at the sensor. A loose or corroded wiring connector can affect the sensor’s output, as can damaged wiring in the circuit between the sensor and PCM. DRIVEABILITY SYMPTOMS If the intake air temperature sensor is not reading accurately, the PCM may think the air is warmer or colder than it actually is, causing it to miscalculate the air/fuel mixture. The result may be a lean or rich fuel mixture that causes driveability symptoms such as poor idle quality when cold, stumble on cold acceleration, and surging when the engine is warm. If the engine computer uses the air temperature sensor input to turn on a cold start injector, and the sensor is not reading accurately, it may prevent the cold start injector from working causing a hard cold start condition.
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Engine Air Temperature Sensor
A faulty air temperature sensor may also affect the operation of the EGR valve is the PCM uses air temperature to determine when the EGR valve opens (on most, it uses the coolant temperature input). On OBD II application (1996 & newer vehicles), a faulty air temperature sensor may prevent the Evaporative (EVAP) Emissions System Monitor from completing. This can prevent a vehicle from passing a plug-in OBD II test (because all the OBD II monitors must run before it can pass the test). The EVAP monitor will only run when the outside temperature is within a certain range (not too cold and not too hot, as a rule). A faulty air temperature sensor that is reading warmer than normal will typically cause in a lean fuel condition. This increases the risk of detonation and lean misfire (which hurts fuel economy and increases emissions). A faulty air temperature sensor that is reading colder than normal will typically cause a rich fuel condition. This wastes fuel and also increases emissions. Sometimes what appears to be a fuel mixture balance problem due to a faulty air temperature sensor is actually due to something else, like an engine vacuum leak or even a restricted catalytic converter! A severe exhaust restriction will reduce intake vacuum and airflow causing the sensor to read hotter than normal (because it is picking up heat from the engine). DIAGNOSING THE AIR TEMPERATURE SENSOR A faulty air temperature sensor may or may not set a code and turn on the Check Engine light. If the sensor circuit is open or shorted, it will usually set a code. But if it is only reading high or low, or is sluggish due to old age or contamination, it usually will not set a code. A quick way to check the air temperature sensor is to use a scan tool to compare the air temperature reading to the coolant temperature reading once the engine is warm. A good air temperature sensor will usually read a few degrees cooler than the coolant sensor. The sensor's resistance can also be checked with an ohmmeter. Remove the sensor, then connect the two leads on the ohmmeter to the two pins in or on the sensor’s wiring connector plug to measure the sensor’s resistance. Measure the sensor’s resistance when it is cold. Then blow hot air at the tip of the sensor with a blow drier (never use a propane torch!) and measure the resistance again. Look for a change in the resistance reading as the sensor warms up. No change in the sensor’s resistance reading as it heats up would tell you the sensor is bad and needs to be replaced. The sensor reading should gradually decrease if the sensor is a negative thermistor, or gradully increase if it is a positive thermistor. If the reading suddenly goes open (infinite resistance) or shorts out (little or no resistance), you have a bad sensor. To be really accurate, you should look up the resistance specifications for the air temperature sensor, then measure the sensor’s resistance at low, mid-range and high temperatures to see if it matches the specifications. A sensor that reads within the specified range when cold, may go out of range at higher temperature, or vice versa. Such a sensor would not be accurate and should be replaced. The resistance and/or voltage test specifications for the air temperature sensor on your engine can be found in a service manual, or by subscribing to the service information on the (Vehicle Mfrs Service Information Website or AlldataDIY. REPLACEMENT/REPAIR/ADJUSTMENT The air temperature sensor is a solid state device so no adjustment is possible. However, it may be possible to clean a dirty sensor so that it functions normally once again provided it is still in good working condition. Contaminants can be removed from the tip of the sensor by (1) removing the sensor from the intake manifold, then (2) spraying the sensor tip with electronics cleaner. For sensors that are mounted inside a MAF sensor, the wire sensing element can also be sprayed with aerosol electronics cleaner. Do not use any other type of cleaner as it may damage the plastic housing or leave behind a chemical residue that may cause problems down the road. If a sensor is not reading within specifications or has failed, replace it. Fortunately, most air temperature are not very expensive (typically less than $30). Dealers always charge more than aftermarket auto parts stores, so shop around and compare prices before you buy. Labor to change an air temperature sensor is usually minimal, unless the sensor is buried
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Engine Air Temperature Sensor
under a lot of other stuff that has to be removed. When replacing the air temperature sensor, be careful not to overtighten it as this may damage the sensor housing, or the threads in a plastic intake manifold. Got an Engine Sensor Problem or Question? Need Help Now? Click the Banner Below to Ask an Expert:
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More Sensor Articles: Making Sense of Engine Sensors Coolant Sensors Crankshaft Position CKP Sensors MAP sensors Mass Airflow MAF Sensors Vane Airflow VAF Sensors Oxygen Sensors Wide Ratio Air Fuel (WRAF) Sensors Throttle Position Sensors Understanding Engine Management Systems Powertrain control modules (PCMs) Flash Reprogramming PCMs All About Onboard Diagnostics II (OBD II) Zeroing in on OBD II Diagnostics Controller Area Network (CAN) Diagnostics OEM Automotive Service Information Websites & Access Fees
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Engine Coolant Sensors
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Engine Coolant Sensors ► Engine Oil Types
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The engine coolant temperature (ECT) sensor is a relatively simple sensor that monitors the internal temperature of the engine. Coolant inside the engine block and cylinder head(s) absorbs heat from the cylinders when the engine is running. The coolant sensor detects the change in temperature and signals the Powertrain Control Module (PCM) so it can tell if the engine is cold, warming up, at normal operating temperature or overheating. The coolant sensor is extremely important because the sensor's input to the PCM affects the operating strategy of the entire engine management system. That's why the coolant sensor is often called the "master" sensor. Many of the fuel, ignition, emissions and drivetrain functions handled by the PCM are affected by the engine's operating temperature. A different operating strategy is used when the engine is cold than when it is warm. This is done to improve cold http://www.aa1car.com/library/coolant_sensors.htm
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driveability, idle quality and emissions. Consequently, if the coolant sensor fails or is giving the PCM a false reading, it can upset a lot of things.
HOW THE COOLANT SENSOR AFFECTS ENGINE OPERATION Input from the coolant sensor may be used by the PCM for any or all of the following control functions: * Start up fuel enrichment on fuel injected engines. When the PCM receives a cold signal from the coolant sensor, it increases injector pulse width (on time) to create a richer fuel mixture. This improves idle quality and prevents hesitation while the cold engine is warming up. As the engine approaches normal operating temperature, the PCM leans out the fuel mixture to reduce emissions and fuel consumption. A faulty coolant sensor that always reads cold may cause the fuel control system to run rich, pollute and waste fuel. A coolant sensor that always reads hot may cause cold driveability problems such as stalling, hesitation and rough idle. * Spark advance and retard. Spark advance is often limited for emission purposes until the engine reaches normal operating temperature. This also affects engine performance and fuel economy. * Exhaust gas recirculation (EGR) during warm-up. The PCM will not allow the EGR valve to open until the engine has warmed up to improve driveability. If EGR is allowed while the engine is still cold, it may cause a rough idle, stalling and/or hesitation. * Evaporative emissions control canister purge. Fuel vapors stored in the charcoal canister are not purged until the engine is warm to prevent driveability problems. * Open/closed loop feedback control of the air/fuel mixture. The PCM may ignore the oxygen sensor rich/lean feedback signal until the coolant reaches a certain temperature. While the engine is cold, the PCM will remain in "open loop" and keep the fuel mixture rich to improve idle quality and cold driveability. If the PCM fails to go into "closed loop" once the engine is warm, the fuel mixture will be too rich causing the engine to pollute and waste gas. This condition may also lead to spark plug fouling. * Idle speed during warm-up. The PCM will usually increase idle speed when a cold engine is first started to prevent stalling and improve idle quality. * Transmission torque converter clutch lockup during warm-up. The PCM may not lockup up the torque converter until the engine has warmed up to improve cold driveability. * Operation of the electric cooling fan. The PCM will cycle the cooling fan on and off to regulate engine cooling using input from the coolant sensor. This job is extremely important to prevent engine overheating. Note: On some vehicles, a separate coolant sensor or fan switch may be used for the cooling fan circuit only.
TYPES OF COOLANT SENSORS Most coolant sensors are "thermistors" that change resistance as the temperature of the coolant changes. Most are the "NTC" (Negative Temperature Coefficient) type where resistance drops as the temperature goes up. With this type of sensor, resistance is high when the engine is cold. As the engine warms up, the internal resistance of the sensor drops until it reaches a minimum value when the engine is at normal operating temperature.
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A typical GM coolant sensor, for example, may have around 10,000 ohms resistance at 32 degrees F and drop to under 200 ohms when the engine is hot (200 degrees). A Ford coolant sensor, by comparison, may read 95,000 ohms at 32 degrees and drop to 2,300 ohms at 200 degrees. Resistance specifications will vary depending on the application, so any sensor that does not read within its specified range should be replaced. Coolant sensors have two wires (input and return). A 5-volt reference voltage signal is sent from the PCM to the sensor. The amount of resistance in the sensor reduces the voltage signal that then returns to the PCM. The PCM then calculates coolant temperature based on the voltage value of the return signal. This number can be displayed on a scan tool, and may also be used by the instrument panel cluster or driver information center to display the temperature reading of the coolant. On some applications, a "dual range" coolant temperature sensor may be used. When the coolant reaches a certain temperature, the PCM changes the reference voltage to the sensor so it can read the coolant temperature with higher accuracy (higher resolution). On some older vehicles, a different type of coolant sensor may be used. Some of these are essentially an on/off switch that opens or closes at a predetermined temperature. The sensor may be wired directly to a relay to turn the electric cooling fan on and off, or it may send a signal to a warning light on the instrument panel. These older coolant sensors are typically single wire sensors. On other older applications, a single wire variable resistor temperature sensor that grounds through the threads may be used to send a temperature signal to a gauge on the instrument panel. These are typically called temperature "senders" rather than sensors.
COOLANT SENSOR LOCATION The coolant sensor is typically located near the thermostat housing in the intake manifold. On a few vehicles, the coolant
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sensor may be located in the cylinder head, or there may be two coolant sensors (one for each cylinder bank in a V6 or V8 engine) or one for the PCM and a second for the cooling fan. The sensor is positioned so the tip will be in direct contact with the coolant. This is essential to produce a reliable signal. If the coolant level is low, it may prevent the coolant sensor from reading accurately.
COOLANT SENSOR SYMPTOMS
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Because of the coolant sensor's central role in triggering so many engine functions, a faulty sensor (or sensor circuit) will often cause cold driveability and emission problems. A bad coolant sensor can also cause a noticeable increase in fuel consumption, and it may cause a vehicle to fail an emissions test if it prevents the engine management system from going into closed loop. Keep in mind that many coolant sensor problems are more often due to wiring faults and loose or corroded connectors than failure of the sensor itself.
The coolant sensor's impact on the engine management system, cold driveability, emissions and fuel economy can also be influenced by the thermostat. If the thermostat is stuck open, the engine will be slow to warm up and the coolant sensor will read low. Or, if someone installed the wrong thermostat for the application or removed the thermostat altogether, it will prevent the engine from reaching normal operating temperature and cause the coolant sensor to read low. A faulty coolant sensor may also cause the engine to overheat if it fails to energize the cooling fan relay when the engine gets hot. A faulty coolant sensor may also cause inaccurate coolant temperature gauge readings on the instrument panel.
COOLANT SENSOR DIAGNOSTIC FAULT CODES On 1996 and newer vehicles with OBD II onboard diagnostic systems, a faulty coolant sensor may prevent some of the system monitors from running. This will prevent the vehicle from passing an OBD II emissions test because the test can't be done unless all the required system monitors have run and passed. The OBD II system should catch the fault, turn on the Check Engine Light or Malfunction Indicator Lamp (MIL), and set one of the following diagnostic trouble codes: P0115....Engine P0116....Engine P0117....Engine P0118....Engine P0119....Engine
Coolant Temperature Coolant Temperature Coolant Temperature Coolant Temperature Coolant Temperature
Circuit Circuit Range/Performance Circuit Low Input Circuit High Input Circuit Intermittent
On older pre-OBD II vehicles, the Check Engine light may come on if the coolant sensor is shorted, open or is reading out of range. GM coolant sensor codes include codes 14 & 15, Ford codes are 21, 51 & 81, and Chrysler codes are 17 & 22.
COOLANT SENSOR DIAGNOSIS A visual inspection of the coolant sensor will sometimes reveal a problem such as severe corrosion around the terminal, a crack in the sensor, or coolant leaks around the sensor. But in most cases, the only way to know if the coolant sensor is good or bad is to measure its resistance and voltage readings. On vehicle systems that provide direct access to sensor data with a scan tool, the coolant sensor's output can usually be displayed in degrees Centigrade (C) or Fahrenheit (F). The coolant sensor should read low (or ambient temperature) when the engine is cold, and high (around 200 degrees) when the engine is hot. No change in the reading or a reading that obviously does not match engine temperature would indicate a faulty sensor or a wiring problem. The internal resistance of a coolant sensor can also be checked with an ohmmeter or DVOM (digital volt ohm meter) and compared to specifications. If the sensor is open, shorted or reads out of range, it must be replaced.
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If the resistance of a coolant sensor is within specifications and changes as engine temperature changes, but the engine is not going into closed loop, the fault is in the wiring or PCM. Further diagnosis will be needed to isolate the problem before any parts are replaced. One trick here is to use a sensor simulator tool to feed a simulated temperature reading through the sensor's wiring harness to the PCM. If the wiring continuity is good but the PCM fails to go into closed loop when you send it a "hot coolant" signal, the problem is in the PCM.
COOLANT SENSOR VOLTAGE CHECKS You can also use a voltmeter or digital storage oscilloscope (DSO) to check the sensor's output. Specs vary, but generally a cold coolant sensor will read somewhere around 3 volts. As the engine warms up and reaches operating temperature, the voltage drop should gradually decrease down to about 1.2 to 0.5 volts. If you're using a scope to display the voltage signal, you should get a trace that gradually slopes from 3 volts down to 1.2 to 0.5 volts in three to five minutes (or however long it normally takes the engine to reach normal operating temperature). If the voltage drop across the coolant sensor reads at or near 5 volts, it means the sensor is open or it has lost its ground connection. If the voltage is close to zero, the sensor is shorted or it has lost its reference voltage. When working on 1985 and up Chrysler products, watch out for a sudden voltage increase as the engine warms up. This is normal and is produced by a 1000 ohm resistor that switches into the coolant sensor circuit when the sensor's voltage drops to about 1.25 volts. This causes the voltage to jump back up to about 3.7 volts, where it again continues to drop until it reaches a fully warmed up value of about 2.0 volts. Sometimes a coolant sensor will suddenly go open or short when it reaches a certain temperature. If your voltmeter has a "minimum/maximum" function, you can catch sudden voltage fluctuations while the sensor is warming up. If you are viewing the voltage pattern on a scope, a short will appear as a sudden drop or dip in the trace to zero volts. An open would make the trace jump up to the VRef voltage line (5 volts). If the coolant sensor reads normally when cold (high resistance and 3 or more volts), but never seems to reach normal temperature it could be telling the truth! An open thermostat or the wrong thermostat may be preventing the coolant from reaching its normal operating temperature.
COOLANT SENSOR REPLACEMENT Most coolant sensors are not replaced unless they have failed. A coolant sensor that is shorted, open or reading out of range obviously can't provide a reliable temperature signal and must be replaced for the engine management system to function properly. But many experts also recommend installing a new coolant sensor if you are replacing or rebuilding an engine. Why? Because coolant sensors can deteriorate with age and may not read as accurately as they did when they were new. Installing a new sensor can eliminate a lot of potential problems down the road. It is also a good idea to replace the coolant sensor and thermostat if the engine has experienced a case of severe overheating. Abnormally high engine temperatures can damage these components and may cause them to misbehave or fail prematurely. Replacing a coolant sensor requires draining some of the coolant from the cooling system. You do not have to drain the entire radiator. Just open the drain valve and let out enough coolant so the coolant level in the engine is below the sensor. This would be a good time to check the condition of the coolant, and to replace it if the coolant is more than three years old (conventional coolant) or five years old (long life coolant). A coolant change and a flush would also be a good idea if the coolant shows any signs of contamination. The threads on the coolant sensor may be pre-coated with sealer to prevent coolant leaks. Tighten the sensor carefully to prevent damage. Once the new sensor has been installed, you can refill the cooling system. Make sure all the air is out of the cooling system. Air trapped under the thermostat may cause the engine to overheat or the coolant sensor to not read correctly.
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Crankshaft & Camshaft Position Sensors
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Crankshaft & Camshaft Position Sensors Copyright AA1Car Distributorless ignition systems require a crankshaft position sensor (CKP), and sometimes also a camshaft position sensor (CMP). These sensors serve essentially the same purpose as the ignition pickup and trigger wheel in an electronic distributor, the only difference being that the basic timing signal is read off the crankshaft or harmonic balancer instead of the distributor shaft. This eliminates ignition timing variations that can result from wear and backlash in the timing chain and distributor gear. It also does away timing adjustments (or misadjustments as the case may be). On 1996 vehicles with Onboard Diagnostics II (OBD II), the crankshaft position sensor is also used to detect variations in crank speed caused by ignition misfire. If the computer senses enough of these, it will illuminate or flash the Check Engine or Service Engine Soon light to signal the driver he has a problem.
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DIFFERENT TYPES OF CRANKSHAFT POSITION SENSORS
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There are a variety of different types of crankshaft position sensors. One is a Hall effect crank position sensor that reads a notched metal "interrupter" ring on the back of the harmonic balancer. This was first used on the early GM 3.8L V6 Buick Sequential Fuel Injection (SFI) engines (and turbos) with distributorless Computer Controlled Coil Ignition (C3I). The crank position sensor provides an on-off signal to the Powertrain Control Module (PCM) that the computer uses to monitor engine rpm and crank position. The system also uses a separate cam position sensor in place of the original distributor to inform the PCM about valve timing. This enables the PCM to determine the correct firing sequence which it then uses to control both injector and ignition timing. Ford uses a similar setup on its 5.0L V8 with distributorless ignition.
Another type of crankshaft position sensor GM uses is the "combination sensor" which you'll find mounted on the front of the 3.0L and 3300 V6. GM calls it a combination sensor because the crank position sensor contains a pair of hall effect switches that generate two separate signals. There are two notched interrupter rings on the back of the harmonic balancer. One ring has three notches which causes one of the hall effect switches to generate three crank position signals every revolution. The other ring has only one notch, which causes the other hall effect switch to generate a single "sync-pulse" signal that the ECM uses to calculate rpm and ignition timing. Another variation of the combination sensor is the "fast start" system used on GM's 3800 engine. A pair of Hall effect switches are mounted by the crank pulley while a cam sensor is mounted over the timing gear. One crank signal generates 3 pulses per revolution while the other generates 18. This allows the coil module to "sync" with the engine more quickly so the engine will start almost instantly. The third type of crankshaft position sensor is a magnetic pickup that reads slots machined in a "reluctor" ring in the center of the crankshaft, on the harmonic balancer or flywheel. This setup is used on GM engines with the Direct Ignition Systems (DIS) on the 2.0L, 2.5L and 2.8L engines, and the Integrated Distributorless Ignition (IDI) on the 2.3L Quad 4, and also many Ford, Chrysler and import engines. On the GM applications, the crank reluctor ring has six equally spaced slots 60 degrees apart. A seventh slot is spaced 10 degrees from one of the others so the crank sensor will generate an extra "sync-pulse" every revolution. The PCM then uses the information to calculate proper ignition and injector timing. This type of sensor must be carefully positioned so the air gap is within .050 in. of the crankshaft reluctor ring.
CKP & CMP SENSOR DIAGNOSIS http://www.aa1car.com/library/crank_sensors.htm
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The fastest way to check the crank and/or camshaft sensors on a 1995 or newer vehicle with OBD II is to plug in your scan tool and check for any fault codes. P0335....Crankshaft Position Sensor A Circuit P0336....Crankshaft Position Sensor A Circuit Range/Performance P0337....Crankshaft Position Sensor A Circuit Low Input P0338....Crankshaft Position Sensor A Circuit High Input P0339....Crankshaft Position Sensor A Circuit Intermittent P0340....Camshaft Position Sensor 'A' Circuit (Bank 1 or Single Sensor) P0341....Camshaft Position Sensor 'A' Circuit Range/Performance (Bank 1) P0342....Camshaft Position Sensor 'A' Circuit Low Input (Bank 1) P0343....Camshaft Position Sensor 'A' Circuit High Input (Bank 1) P0344....Camshaft Position Sensor 'A' Circuit Intermittent (Bank 1) P0345....Camshaft Position Sensor 'A' Circuit (Bank 2) P0346....Camshaft Position Sensor 'A' Circuit Range/Performance (Bank 2) P0347....Camshaft Position Sensor 'A' Circuit Low Input (Bank 2) P0348....Camshaft Position Sensor 'A' Circuit High Input (Bank 2) P0349....Camshaft Position Sensor 'A' Circuit Intermittent (Bank 2) You can also use your scan tool to check for the presence of a cranking rpm signal if an engine is cranking but is not starting because there is no spark (which is often a clue that the crankshaft position sensor is not working). On pre-OBD II vehicles, you can use a scan tool to check for codes, or use a manual flash code procedure to read out codes. On a pre-OBD II GM application, a trouble Code 12 while cranking would indicate no reference signal being generated. On pre-OBD II Ford applications, a Code 14 would indicate a problem with the crank position sensor signal, which Ford calls a "PIP" (Profile Ignition Pick-up) signal. CRANK POSITION SENSOR CHECKS Whether a crankshaft position sensor is the magnetic type or a hall effect switch, most problems can be traced to faults in the wiring harness. A disruption of the sensor supply voltage, ground or return circuits can cause a loss of the all-important timing signal resulting in an engine that cranks but won't start. Also, on some vehicles, damage to the notched sensor ring on the crankshaft, harmonic balancer or flywheel can cause an erratic crankshaft sensor signal. When troubleshooting a suspected crankshaft position sensor problem, you should follow the diagnostic flow charts in the vehicle manufacturer's service literature to isolate the faulty component when a fault code is present, otherwise there is no way to know if a no-spark starting problem is a bad ignition module, coil, computer, wiring fault or ignition switch. Magnetic sensors can be checked by unplugging the electrical connector and checking resistance between the appropriate terminals. On a GM 2.3L Quad 4, for example, the sensor should read between 500 and 900 ohms. Always refer to the vehicle manufacturers test specifications when testing these sensors. Obviously, if you see a zero resistance reading (shorted) or an infinite (open) reading, the sensor has failed and needs to be replaced. If viewed on an oscilloscope, a magnetic crank sensor will produce a waveform similar to that below:
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Digital and analog crank sensor waveforms as they would appear on a DSO scope. A good magnetic crank position sensor should produce an alternating current when the engine is cranked, so a voltage output check while cranking is another test that can be performed. With the sensor connected, read the output voltage across the appropriate terminals while cranking the engine. If you see at least 20 mV on the AC scale, the sensor is good, meaning the fault is probably in the module, coil, wiring or computer. Hall effect crankshaft position sensors typically have three terminals; one for current feed, one for ground and one for the output signal. The sensor must have voltage and ground to produce a signal, so check these terminals first with an analog voltmeter. Sensor output can be checked by disconnecting the coil and cranking the engine to see if the sensor produces a voltage signal. The voltmeter needle should jump each time a shutter blade passes through the Hall effect switch. If observed on an oscilloscope, you should see a square wave form (see above) that changes in frequency. If your diagnosis reveals a faulty crank sensor, the only option is to replace it. With Hall effect sensors, the sensor must be properly aligned with the interrupter ring to generate a clean signal. Any rubbing or interference could cause idle problems as well as sensor damage. Magnetic crankshaft position sensors must be installed with the proper air gap, which is usually within .050 in. of the reluctor wheel on the crankshaft. CAMSHAFT POSITION SENSORS On many engines with distributorless ignition systems and sequential fuel injection, a camshaft position sensor is used to keep the engine's control module informed about the position of the camshaft relative to the crankshaft. By monitoring cam position (which allows the control module to determine when the intake and exhaust valves are opening and closing), the control module can use the cam position sensor's input along with that from the crankshaft position sensor to determine which cylinder in the engine's firing sequence is approaching top dead center. This information is then used by the engine control module to synchronize the pulsing of sequential fuel injectors so they match the firing order of the engine. On some applications, input from the camshaft position sensor is also required for ignition timing. The camshaft position sensor may be magnetic or Hall effect, and mounted on the timing cover over the camshaft gear, on the end of the cylinder head in an overhead cam application, or in a special housing that replaces the distributor (in the case of some of the GM applications). Operation and diagnosis is essentially the same as that for a crankshaft position sensor.
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OXYGEN SENSORS
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Oxygen Sensors: How to Diagnose and Replace Copyright AA1Car Computerized engine control systems rely on inputs from a variety of sensors to regulate engine performance, emissions and other important functions. The sensors must provide accurate information otherwise driveability problems, increased fuel consumption and emission failures can result. The Oxygen Sensor is one of the key sensors in this system. It is often referred to as the "O2" sensor because O2 is the chemical formula for oxygen (oxygen atoms always travel in pairs, never alone). It may also be referred to as the H2O2 for Heated Oxygen Sensor because it has an internal heater circuit to bring the sensor up to operating temperature following a cold start. The first O2 sensor was introduced in 1976 on a Volvo 240. California vehicles got them next in 1980 when California's emission rules required lower emissions. Federal emission laws made O2 sensors virtually mandatory on all cars and light trucks built since 1981. And now that OBD-II regulations are here (1996 and newer vehicles), many vehicles are now equipped with multiple O2 sensors, some as many as four!
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Oxygen sensor internal components The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as the exhaust exits the engine. Monitoring oxygen levels in the exhaust is a way of gauging the fuel mixture. It tells the computer if the fuel mixture is burning rich (less oxygen) or lean (more oxygen). A lot of factors can affect the relative richness or leanness of the fuel mixture, including air temperature, engine coolant temperature, barometric pressure, throttle position, air flow and engine load. There are other sensors to monitor these factors, too, but the O2 sensor is the master monitor for what is happening with the fuel mixture. Consequently, any problems with the O2 sensor can throw the whole system out of whack. FUEL MIXTURE FEEDBACK CONTROL LOOP
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The computer uses the oxygen sensor input to regulate the fuel mixture, which is referred to as the fuel "feedback control loop." The computer takes its cues from the O2 sensor and responds by changing the fuel mixture. This produces a corresponding change in the O2 sensor reading. This is referred to as "closed loop" operation because the computer is using the O2 sensor's input to regulate the fuel mixture. The result is a constant flip-flop back and forth from rich to lean which allows the catalytic converter to operate at peak efficiency while keeping the average overall fuel mixture in proper balance to minimize emissions. It is a complicated setup but it works. When no signal is received from the O2 sensor, as is the case when a cold engine is first started (or the 02 sensor fails), the computer orders a fixed (unchanging) rich fuel mixture. This is referred to as "open loop" operation because no input is used from the O2 sensor to regulate the fuel mixture. If the engine fails to go into closed loop when the O2 sensor reaches operating temperature, or drops out of closed loop because the O2
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sensor signal is lost, the engine will run too rich causing an increase in fuel consumption and emissions. A bad coolant sensor can also prevent the system from going into closed loop because the computer also considers engine coolant temperature when deciding whether or not to go into closed loop. HOW AN OXYGEN SENSOR WORKS The O2 sensor works like a miniature generator and produces its own voltage when it gets hot. Inside the vented cover on the end of the sensor that screws into the exhaust manifold is a zirconium ceramic bulb. The bulb is coated on the outside with a porous layer of platinum. Inside the bulb are two strips of platinum that serve as electrodes or contacts. The outside of the bulb is exposed to the hot gases in the exhaust while the inside of the bulb is vented internally through the sensor body to the outside atmosphere. Older style oxygen sensors actually have a small hole in the body shell so air can enter the sensor, but newer style O2 sensors "breathe" through their wire connectors and have no vent hole. It is hard to believe, but the tiny amount of space between the insulation and wire provides enough room for air to seep into the sensor (for this reason, grease should never be used on O2 sensor connectors because it can block the flow of air). Venting the sensor through the wires rather than with a hole in the body reduces the risk of dirt or water contamination that could foul the sensor from the inside and cause it to fail. The difference in oxygen levels between the exhaust and outside air within the sensor causes voltage to flow through the ceramic bulb. The greater the difference, the higher the voltage reading. An oxygen sensor will typically generate up to about 0.9 volts when the fuel mixture is rich and there is little unburned oxygen in the exhaust. When the mixture is lean, the sensor output voltage will drop down to about 0.2 volts or less. When the air/fuel mixture is balanced or at the equilibrium point of about 14.7 to 1, the sensor will read around .45 volts.
When the computer receives a rich signal (high voltage) from the O2 sensor, it leans the fuel mixture to reduce the sensor's feedback voltage. When the O2 sensor reading goes lean (low voltage), the computer reverses again making the fuel mixture go rich. This constant flip-flopping back and forth of the fuel mixture occurs with different speeds depending on the fuel system. The transition rate is slowest on engines with feedback carburetors, typically once per second at 2500 rpm. Engines with throttle body injection are somewhat faster (2 to 3 times per second at 2500 rpm), while engines with multiport injection are the fastest (5 to 7 times per second at 2500 rpm).
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The oxygen sensor must be hot (about 600 degrees or higher) before it will start to generate a voltage signal, so many oxygen sensors have a small heating element inside to help them reach operating temperature more quickly. The heating element can also prevent the sensor from cooling off too much during prolonged idle, which would cause the system to revert to open loop. Heated O2 sensors are used mostly in newer vehicles and typically have 3 or 4 wires. Older single wire O2 sensors do not have heaters. When replacing an O2 sensor, make sure it is the same type as the original (heated or unheated) A NEW ROLE FOR O2 SENSORS WITH OBD II Starting with a few vehicles in 1994 and 1995, and all 1996 and newer vehicles, the number of oxygen sensors per engine has doubled. A second oxygen sensor is now used downstream of the catalytic converter to monitor converter operating efficiency. On V6 or V8 engines with dual exhausts, this means up to four O2 sensors (one for each cylinder bank and one after each converter) may be used.
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The OBD II system is designed to monitor the emissions performance of the engine. This includes keeping an eye on anything that might cause emissions to increase. The OBD II system compares the oxygen level readings of the O2 sensors before and after the converter to see if the converter is reducing the pollutants in the exhaust. If it sees little or no change in oxygen level readings, it means the converter is not working properly. This will cause the Malfunction Indicator Lamp (MIL) to come on.
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Watch O2 Sensor Diagnosis Video OXYGEN SENSOR DIAGNOSIS O2 sensors are amazingly rugged considering the operating environment they live in. But O2 sensors do wear out and eventually have to be replaced. The performance of the O2 sensor tends to diminish with age as contaminants accumulate on the sensor tip and gradually reduce its ability to produce voltage. This kind of deterioration can be caused by a variety of substances that find their way into the exhaust such as lead, silicone, sulfur, oil ash and even some fuel additives. The sensor can also be damaged by environmental factors such as water, splash from road salt, oil and dirt. As the sensor ages and becomes sluggish, the time it takes to react to changes in the air/fuel mixture slows down which causes emissions to go up. This happens because the flip-flopping of the fuel mixture is slowed down which reduces converter efficiency. The effect is more noticeable on engines with multiport fuel injection (MFI) than electronic carburetion or throttle body injection because the fuel ratio changes much more rapidly on MFI applications. If the sensor dies altogether, the result can be a fixed, rich fuel mixture. Default on most fuel injected applications is midrange after three minutes. This causes a big jump in fuel consumption as well as emissions. And if the converter overheats because of the rich mixture, it may suffer damage. One EPA study found that 70% of the vehicles that failed an I/M 240 emissions test needed a new O2 sensor. Most O2 sensor problems will cause the OBD II system to set one or more diagnostic trouble codes (DTCs) and turn on the Check Engine light. These are the OBD codes associated with O2 sensor faults: P0030....HO2S Heater Control Circuit Bank 1 Sensor 1 P0031....HO2S Heater Control Circuit Low Bank 1 Sensor 1 P0032....HO2S Heater Control Circuit High Bank 1 Sensor 1 P0033....Turbo Charger Bypass Valve Control Circuit P0034....Turbo Charger Bypass Valve Control Circuit Low P0035....Turbo Charger Bypass Valve Control Circuit High P0036....HO2S Heater Control Circuit Bank 1 Sensor 2 P0037....HO2S Heater Control Circuit Low Bank 1 Sensor 2 P0038....HO2S Heater Control Circuit High Bank 1 Sensor 2 P0042....HO2S Heater Control Circuit Bank 1 Sensor 3 P0043....HO2S Heater Control Circuit Low Bank 1 Sensor 3 P0044....HO2S Heater Control Circuit High Bank 1 Sensor 3 P0050....HO2S Heater Control Circuit Bank 2 Sensor 1 P0051....HO2S Heater Control Circuit Low Bank 2 Sensor 1 P0052....HO2S Heater Control Circuit High Bank 2 Sensor 1 P0056....HO2S Heater Control Circuit Bank 2 Sensor 2 P0057....HO2S Heater Control Circuit Low Bank 2 Sensor 2 P0058....HO2S Heater Control Circuit High Bank 2 Sensor 2
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P0062....HO2S Heater Control Circuit Bank 2 Sensor 3 P0063....HO2S Heater Control Circuit Low Bank 2 Sensor 3 P0064....HO2S Heater Control Circuit High Bank 2 Sensor 3 P0130....O2 Sensor Circuit Bank 1 Sensor 1 P0131....O2 Sensor Circuit Low Voltage Bank 1 Sensor 1 P0132....O2 Sensor Circuit High Voltage Bank 1 Sensor 1 P0133....O2 Sensor Circuit Slow Response Bank 1 Sensor 1 P0134....O2 Sensor Circuit No Activity Detected Bank 1 Sensor 1 P0135....O2 Sensor Heater Circuit Bank 1 Sensor 1 P0136....O2 Sensor Circuit Malfunction Bank 1 Sensor 2 P0137....O2 Sensor Circuit Low Voltage Bank 1 Sensor 2 P0138....O2 Sensor Circuit High Voltage Bank 1 Sensor 2 P0139....O2 Sensor Circuit Slow Response Bank 1 Sensor 2 P0140....O2 Sensor Circuit No Activity Detected Bank 1 Sensor 2 P0141....O2 Sensor Heater Circuit Bank 1 Sensor 2 P0142....O2 Sensor Circuit Malfunction Bank 1 Sensor 3 P0143....O2 Sensor Circuit Low Voltage Bank 1 Sensor 3 P0144....O2 Sensor Circuit High Voltage Bank 1 Sensor 3 P0145....O2 Sensor Circuit Slow Response Bank 1 Sensor 3 P0146....O2 Sensor Circuit No Activity Detected Bank 1 Sensor 3 P0147....O2 Sensor Heater Circuit Bank 1 Sensor 3 If an O2 sensor is marginally sluggish or is slightly biased rich or lean, it may not set a fault code. The only way to know if the O2 sensor is functioning normally is to check its responsiveness to changes in the air/fuel mixture. You can read the O2 sensor's voltage output with a scan tool or digital voltmeter, but the transitions are hard to see because the numbers jump around so much. The best way to observe O2 sensor output voltage changes is with a Digital Storage Oscilloscope (DSO). A scope will display the sensor voltage output as a wavy line that shows both it's amplitude (minimum and maximum voltage) as well as its frequency (transition rate from rich to lean).
A good O2 sensor should produce an oscillating waveform at idle that makes voltage transitions from near minimum (0.1 v) to near maximum (0.9v). Making the fuel mixture artificially rich by feeding propane into the intake manifold should cause the sensor to respond almost immediately (within 100 milliseconds) and go to maximum (0.9v) output. Creating a lean mixture by opening a vacuum line should cause the sensor output to drop to its minimum (0.1v) value. If the sensor does not flip-flop back and forth quickly enough, it may indicate a need for replacement. If the O2 sensor circuit opens, shorts or goes out of range, it may set a fault code and illuminate the Check Engine or Malfunction Indicator Lamp. If additional diagnosis reveals the sensor is defective, replacement is required. But many O2 sensors that are badly degraded continue to work well enough not to set a fault code, but not well enough to prevent an increase in emissions and fuel consumption. The absence of a fault code or warning lamp, therefore, does not mean the O2
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sensor is functioning properly. The sensor may be lazy, or biased rich or lean. A company called Lenehan Research makes a handheld O2 sensor tester that checks the response time of the O2 sensor to show if it is good or bad. The tester requires the oxygen sensor to jump from below 175mV to above 800mV in less than 100mS when the throttle is snapped. If the sensor does not respond quickly enough it fails the test. The tester also shows closed loop operation on a fast, ultra-bright, colored 10 LED display, and tests the PCM control of the fuel feedback control system. OXYGEN SENSOR REPLACEMENT Any O2 sensor that is defective obviously needs to be replaced. But there may also be benefits to replacing the O2 sensor periodically for preventative maintenance. Replacing an aging O2 sensor that has become sluggish can restore peak fuel efficiency, minimize exhaust emissions and prolong the life of the converter. Unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s vehicles can be replaced every 30,000 to 50,000 miles. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 miles. On OBD II equipped vehicles (1996 & up), a replacement interval of 100,000 miles can be recommended. The oxygen sensor can be removed from the exhaust manifold using a special oxygen sensor socket (which has a cutout to clear the wires), or a 22mm socket. The sensor will come out easier if the engine is slightly warm but not hot to the touch. Place the socket over the sensor and turn counterclockwise to loosen it. If it is frozen, apply penetrating oil and heat around the base of the sensor. When installing a new "direct fit" or OEM oxygen sensor, the wiring connector on the new sensor will plug into the connector with no modifications needed. But if you are installing a "universal" oxygen sensor, the original wiring connector will have to be cut off so the wires on the new sensor can be spliced to the wires that went to the connector. With 4-wire sensors, one wire is the signal wire, one is ground, and the other two are for the heater circuit. The wires are color coded, but the colors on the universal sensor probably won't match those on the original sensor. See the chart below from the color coding used on various brands of oxygen sensors:
Typical oxygen sensor wiring color codes.
Oxygen Sensor Q & A How many oxygen sensors are on today's engines? It depends on the model year and type of engine. On most four and straight six cylinder engines, there is usually a single oxygen sensor mounted in the exhaust manifold. On V6, V8 and V10 engines, there are usually two oxygen sensors, one in http://www.aa1car.com/library/o2sensor.htm
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each exhaust manifold. This allows the computer to monitor the air/fuel mixture from each bank of cylinders. On later model vehicles with OBD II (some 1993 and '94 models, and all 1995 and newer models), one or two additional oxygen sensors are also mounted in or behind the catalytic converter to monitor converter efficiency. These are referred to as the downstream O2 sensors, and thee will be one for each converter if the engine has dual exhausts with separate converters. How are the oxygen sensors identified on a scan tool? When displayed on a scan tool, the right and left upstream oxygen sensors are typically labeled Bank 1, Sensor 1 and Bank 2, Sensor 1. The Bank 1 sensor will always be on the same side of a V6 or V8 engine as cylinder number one. On a scan tool, the downstream sensor on a four or straight six cylinder engine with single exhaust is typically labeled Bank 1, Sensor 2. On a V6, V8 or V10 engine, the downstream O2 sensor might be labeled Bank 1 or Bank 2, Sensor 2. If a V6, V8 or V10 engine has dual exhausts with dual converters, the downstream O2 sensors would be labeled Bank 1, Sensor 2 and Bank 2, Sensor 2. Or, the downstream oxygen sensor might be labeled Bank 1 Sensor 3 if the engine has two upstream oxygen sensors in the exhaust manifold (some do to more accurately monitor emissions). It's important to know how the O2 sensors are identified because a diagnostic trouble code that indicates a faulty O2 sensor requires a specific sensor to be replaced. Bank 1 Sensor 1 might be the back O2 sensor on a transverse V6, or it might be the one on the front exhaust manifold. What's more, the O2 sensors on a transverse engine might be labeled differently than those on a rear-wheel drive application. There is not a lot of consistency as from one vehicle manufacturer to another as to how O2 sensors are labeled, so always refer to the OEM service literature to find out which sensor is Bank 1 Sensor 1 and which one is Bank 2 Sensor 1. This information can be difficult to find. Some OEMs clearly identify which O2 sensor is which but others do not. If in doubt, call a dealer and ask somebody in the service department. For Oxygen Sensor Locations, Click Here.
How does a downstream O2 sensor monitor converter efficiency? A downstream oxygen sensor in or behind the catalytic converter works exactly the same as an upstream O2 sensor in the exhaust manifold. The sensor produces a voltage that changes when the amount of unburned oxygen in the exhaust changes. If the O2 sensor is a traditional zirconia type sensor, the voltage output drops to about 0.2 volts when the fuel mixture is lean (more oxygen in the exhaust). When the fuel mixture is rich (less oxygen in the exhaust), the sensor's output jumps up to a high of about 0.9 volts. The high or low voltage signal tells the PCM the fuel mixture is rich or lean. On some newer vehicles, a new type of Wide Ratio Air Fuel (WRAF) Sensor is used. Instead of producing a high or low voltage signal, the signal changes in direct proportion to the amount of oxygen in the exhaust. This provides a more precise measurement for better fuel control. These sensors are also called wideband oxygen sensors because they can read very lean air/fuel mixtures. The OBD II system monitors converter efficiency by comparing the upstream and downstream oxygen sensor signals. If the converter is doing its job and is reducing the pollutants in the exhaust, the downstream oxygen sensor should show little activity (few lean-to-rich transitions, which are also called "crosscounts"). The sensor's voltage reading should also be fairly steady (not changing up or down), and average 0.45 volts or higher. If the signal from the downstream oxygen sensor starts to mirror that from the upstream oxygen sensor(s), it means converter efficiency has dropped off and the converter isn't cleaning up the pollutants in the exhaust. The threshold for setting a diagnostic trouble code (DTC) and turning on the Malfunction Indicator Lamp (MIL) is when emissions are estimated to exceed federal limits by 1.5 times. See Troubleshooting a P0420 Catalyst Code for more info about converter problems. If converter efficiency had declined to the point where the vehicle may be exceeding the pollution limit, the PCM will turn on the Malfunction Indicator Lamp (MIL) and set a diagnostic trouble code. At that point, additional diagnosis may be needed to confirm the failing converter. If the upstream and downstream O2 sensors are functioning properly and show a drop off in converter efficiency, the converter must be replaced to restore emissions compliance. The vehicle will not pass an OBD II emissions test if there are any converter codes in the PCM. http://www.aa1car.com/library/o2sensor.htm
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What's the difference between a "heated" and "unheated" oxygen sensor? Heated oxygen sensors have an internal heater circuit that brings the sensor up to operating temperature more quickly than an unheated sensor. An oxygen sensor must be hot (about 600 to 650 degrees F) before it will generate a voltage signal. The hot exhaust from the engine will provide enough heat to bring an O2 sensor up to operating temperature, but it make take several minutes depending on ambient temperature, engine load and speed. During this time, the fuel feedback control system remains in "open loop" and does not use the O2 sensor signal to adjust the fuel mixture. This typically results in a rich fuel mixture, wasted fuel and higher emissions. By adding an internal heater circuit to the oxygen sensor, voltage can be routed through the heater as soon as the engine starts to warm up the sensor. The heater element is a resistor that glows red hot when current passes through it. The heater will bring the sensor up to operating temperature within 20 to 60 seconds depending on the sensor, and also keep the oxygen sensor hot even when the engine is idling for a long period of time. Heated O2 sensors typically have two-three or four wires (the extra wires are for the heater circuit). Note: Replacement O2 sensors must have the same number of wires as the original, and have the same internal resistance. The OBD II system also monitors the heater circuit and will set a trouble code if the heater circuit inside the O2 sensor is defective. The heater is part of the sensor and cannot be replaced separately, so if the heater circuit is open or shorted and the problem is not in the external wiring or sensor connector, the O2 sensor must be replaced.
For Professional Technicians Only: An Oxygen Sensor Recycling Program NGK, a supplier of new oxygen sensors, has created an oxygen sensor recycling program for professional technicians. NGK says it will accept any brand of oxygen sensor for recycling. The program allows the small amount of platinum inside the sensor element to be recovered and reused. For details, go to http://ntkssrp.com/.
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Related Engine Sensor Articles: Wideband O2 Sensors & A/F Sensors Oxygen Sensor Locations Sensing Emission Problems (O2 Sensors) Making Sense of Engine Sensors Understanding Engine Management Systems Powertrain control modules (PCMs) All About Onboard Diagnostics II (OBD II) Zeroing in on OBD II Diagnostics OBD Monitor Not Ready Catalytic Converters Troubleshooting a P0420 Catalyst Code Poor Fuel Economy (causes of)
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Oxygen Sensor Locations
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Oxygen Sensor Locations Copyright AA1Car When troubleshooting oxygen sensor problems with a scan tool, you may find a diagnostic trouble code for one of the O2 sensors. The code displayed on your scan tool will indicate the type of fault, and identify one of the oxygen sensors by its position in the exhaust system. The oxygen sensor's location will be identified by position (sensor 1, sensor 2 or sensor 3), and by cylinder bank (bank 1 or bank 2). Most late model engines have multiple oxygen sensors, so which one is sensor 1, 2 or 3, and how do you know which cylinder bank is 1 or 2? On straight four and six cylinder engines, there is only one bank of cylinders. So all of the oxygen sensors will be bank 1. The oxygen sensor or Air/Fuel sensor closest to the engine in the exhaust manifold will always be Sensor 1. The O2 sensor located in or behind the catalytic converter will be Sensor 2. On V6 and V8 engines, Sensor 1 will always be on the SAME side as the Number ONE cylinder in the engine's firing order. On Ford V6 and V8 engines, for example, cylinder number one is typically the RIGHT front cylinder on the passenger side in a rear-wheel drive car or truck. On a Ford front-wheel drive car or minivan with a transverse (sideways) mounted engine, the number one cylinder is on the back side of the engine (closest to the firewall) on the right (passenger side) of the engine. On GM and Chrysler V6 and V8 engines, cylinder number one is typically the LEFT front cylinder on the driver's side in a rear-wheel drive car or truck. On a GM front-wheel drive car or minivan with a transverse (sideways) mounted engine, the number one cylinder is on the front side of the engine (closest to the radiator) on the right (passenger side) of the engine. On a Chrysler front-wheel drive car or minivan with a transverse (sideways) mounted engine, the number one cylinder is on the back side of the engine (closest to the firewall) on the right (passenger side) of the engine (like a Ford). To look up the firing orders for various engines, use the following links: Firing Orders (Chevy) Firing Orders (Chrysler) Firing Orders (Ford) The location of the number one cylinder on import engines will vary depending on the year/make/model. One way to find number one cylinder so you can identify bank 1 is to look at the ignition system. If it has a distributorless ignition system (DIS) or a coil-on-plug (COP) ignition, the plug wires or coils may have lettering or marking indicating the cylinder numbers. If a V6, V8 or V10 engine has dual exhausts with dual converters, the downstream O2 sensors would be labeled Bank 1, Sensor 2 and Bank 2, Sensor 2. Or, the downstream oxygen sensor might be labeled Bank 1 Sensor 3 if the engine has two upstream oxygen sensors in the exhaust manifold (some do to more accurately monitor emissions).
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It's important to accurately identify which oxygen sensor is which so you can replace the correct sensor. Oxygen sensors are expensive and difficult to replace, so you want to make sure you have the correct location before you replace anything.
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Related Articles: Oxygen Sensors Wide Ratio Air Fuel (WRAF) Sensors Sensing Emission Problems (O2 Sensors) Making Sense of Engine Sensors Understanding Engine Management Systems Powertrain control modules (PCMs) All About Onboard Diagnostics II (OBD II) Zeroing in on OBD II Diagnostics Catalytic Converters Troubleshooting a P0420 Catalyst Code
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Wideband O2 Sensors and Air/Fuel (A/F) Sensors
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Wideband O2 Sensors and Air/Fuel (A/F) Sensors Copyright AA1Car Wideband Oxygen sensors (which may also be called Wide Range Air Fuel (WRAF) sensors) and Air/Fuel (A/F) Sensors, are replacing conventional oxygen sensors in many late model vehicles. A wideband O2 sensor or A/F sensor is essentially a smarter oxygen sensor with some additional internal circuitry that allows it to precisely determine the exact air/fuel ratio of the engine. Like an ordinary oxygen sensor, it reacts to changing oxygen levels in the exhaust. But unlike an ordinary oxygen sensor, the output signal from a wideband O2 sensor or A/F sensor does not change abruptly when the air/fuel mixture goes rich or lean. This makes it better suited to today's low emission engines, and also for tuning performance engines.
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Oxygen Sensor Outputs An ordinary oxygen sensor is really more of a rich/lean indicator because its output voltage jumps up to 0.8 to 0.9 volts when the air/fuel mixture is rich, and drops to 0.3 volts or less when the air/fuel mixture is lean. By comparison, a wideband O2 sensor or A/F sensor provides a gradually changing current signal that corresponds to the exact air/fuel ratio. Another difference is that the sensor's output voltage is converted by its internal circuitry into a variable current signal that can travel in one of two directions (positive or negative). The current signal gradually increases in the positive direction when the air/fuel mixture becomes leaner. At the "stoichiometric" point when the air/fuel mixture is perfectly balanced (14.7 to 1), which is also referred to as "Lambda", the current flow from the sensor stops and there is no current flow in either direction. And when the air/fuel ratio becomes progressively richer, the current reverses course and flows in the negative direction. The PCM sends a control reference voltage (typically 3.3 volts on Toyota A/F sensor applications, 2.6 volts on Bosch and GM wideband sensors) to the sensor through one pair of wires, and monitors the sensor's output current through a second set of wires. The sensor's output signal is then processed by the PCM, and can be read on a scan tool as the air/fuel ratio, a fuel trim value and/or a voltage value depending on the application and the display capabilities of the scan tool. For applications that display a voltage value, anything less than the reference voltage indicate a rich air/fuel ratio while voltages above the reference voltage indicates a lean air/fuel ratio. On some of the early Toyota OBD II applications, the PCM converts the A/F sensor voltage to look like that of an ordinary oxygen sensor (this was done to comply with the display requirements of early OBD II regulations).
How a Wideband O2 Sensor Works Internally, wideband O2 sensors and A/F sensors appear to be similar to conventional zirconia planar oxygen sensors. There is a flat ceramic strip inside the protective metal nose cone on the end of the sensor. The ceramic strip is actually a dual sensing element that combines a "Nerst effect" oxygen pump and "diffusion gap" with the oxygen sensing element. All three are laminated on the same strip of ceramic.
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Wideband O2 Sensors and Air/Fuel (A/F) Sensors
Exhaust gas enters the sensor through vents or holes in the metal shroud over the tip of the sensor and reacts with the dual sensor element. Oxygen diffuses through the ceramic substrate on the sensor element. The reaction causes the Nerst cell to generate a voltage just like an ordinary oxygen sensor. The oxygen pump compares the change in voltage to the control voltage from the PCM, and balances one against the other to maintain an internal oxygen balance. This alters the current flow through the sensor creating a positive or negative current signal that indicates the exact air/fuel ratio of the engine. The current flow is not much, usually only about 0.020 amps or less. The PCM then converts the sensor's analog current output into a voltage signal that can then be read on your scan tool. What's the difference between a wideband O2 sensor and an A/F sensor? Wideband 2 sensors typically have 5 wires while most A/F sensors have 4 wires.
O2 SENSOR HEATER CIRCUIT Like ordinary oxygen sensors, wideband O2 sensors and A/F sensors also have an internal heater circuit to help them reach operating temperature quickly. To work properly, wideband and A/F sensors require a higher operating temperature: 1292 to 1472 degrees F versus about 600 degrees F for ordinary oxygen sensors. Consequently, if the heater circuit fails, the sensor may not put out a reliable signal. The heater circuit is energized through a relay, which turns on when the engine is cranked and the fuel injection relay is energized. The heater circuit can pull up to 8 amps on some engines, and is usually pulse width modulated (PWM) to vary the amount of heat depending on engine temperature (this also prevents the heater from getting too hot and burning out). When the engine is cold, the duty ratio (on time) of the heater circuit will be higher than when the engine is hot. A failure in the heater circuit will usually turn on the Malfunction Indicator Lamp (MIL) and set a P0125 diagnostic trouble code (DTC).
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Oxygen Sensor Problems Like ordinary oxygen sensors, wideband O2 sensors and A/F sensors are vulnerable to contamination and aging. They can become sluggish and slow to respond to changes in the air/fuel mixture as contaminants build up on the sensor element. Contaminants include phosphorus from motor oil (from worn valve guides and rings), silicates from antifreeze (leaky head gasket or intake gaskets, or cracks in the combustion chamber that leak coolant), and even sulfur and other additives in gasoline. The sensors are designed to last upwards of 150,000 miles but may not go the distance if the engine burns oil, develops an internal coolant leak or gets some bad gas. Wideband 2 sensors and A/F sensors can also be fooled by air leaks in the exhaust system (leaky exhaust manifold gaskets) or compression problems (such as leaky or burned exhaust valves) that allow unburned air to pass through the engine and enter the exhaust.
Wideband A/F Sensor Diagnostics As a rule, the OBD II system will detect any problems that affect the operation of the oxygen or A/F sensors and set a DTC that corresponds to the type of fault. Generic OBD II codes that indicate a fault in the O2 or A/F sensor heater circuit include: P0036, P0037, P0038, P0042, P0043, P0044, P0050, P0051, P0052, P0056, P0057, P0058, P0062, P0063, P0064. Codes that indicate a possible fault in the oxygen sensor itself include any code from P0130 to P0167. There may be additional OEM "enhanced "P1" codes that will vary depending on the year, make and model of the vehicle. The symptoms of a bad wideband O2 sensor or A/F sensor are essentially the same as those of a conventional oxygen sensor: Engine running rich, poor fuel economy and/or an emission failure due to higher than normal levels of carbon monoxide (CO) in the exhaust. Possible causes in addition to the sensor itself having failed include bad wiring connections or a faulty heater circuit relay (if there are heater codes), or a wiring fault, leaky exhaust manifold gasket or leaky exhaust valves if there are sensor codes indicating a lean fuel condition.
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Wideband O2 Sensors and Air/Fuel (A/F) Sensors
What to Check: How the sensor responds to changes in the air/fuel ratio. Plug a scan tool into the vehicle diagnostic connector, start the engine and create a momentary change in the air/fuel radio by snapping the throttle or feeding propane into the throttle body. Look for a response from the wideband O2 sensor or A/F sensor. No change in the indicated air/fuel ratio, Lambda value, sensor voltage value or short term fuel trim number would indicate a bad sensor that needs to be replaced. Other scan tool PIDS to look at include the OBD II oxygen heater monitor status, OBD II oxygen sensor monitor status, loop status and coolant temperature. The status of the monitors will tell you if the OBD II system has run its self-checks on the sensor. The loop status will tell you if the PCM is using the wideband O2 or A/F sensor's input to control the air/fuel ratio. If the system remains in open loop once the engine is warm, check for a possible faulty coolant sensor. Another way to check the output of a wideband O2 sensor or A/F sensor is to connect a digital voltmeter or graphing multimeter in series with the sensor's voltage reference line (refer to a wiring diagram for the proper connection). Connect the black negative lead to the sensor end of the reference wire, and the red positive lead to the PCM end of the wire. The meter should then show an increase in voltage (above the reference voltage) if the air/fuel mixture is lean, or a drop in voltage (below the reference voltage) if the mixture is rich. The output of a wideband O2 sensor or A/F sensor can also be observed on a digital storage oscilloscope by connecting one lead to the reference circuit and the other to the sensor control circuit. This will generate a waveform that changes with the air/fuel ratio. The scope can also be connected to the sensor's heater wires to check the duty cycle of the heater circuit. You should see a square wave pattern and a decrease in the duty cycle as the engine warms up.
Wideband Oxygen Sensor Tech Tips * On Honda 5-wire "Lean Air Fuel" (LAF) sensors, the 8-pin connector pin for the sensor contains a special "calibration" resistor. The value of the resistor can be determined by measuring between terminals 3 and 4 with an ohmmeter, and will be 2.4K ohms, 10K ohms or 15k ohms depending on the application. If the connector is damaged and must be replaced, the replacement must have the same value as the original. The reference voltage from the PCM to the sensor on these engines is 2.7 volts. * Saturn also uses a special trim resistor in their wideband O2 sensor connector (pins 1 & 6). The resistor is typically 30 to 300 ohms. The PCM supplied reference voltage is 2.4 to 2.6 volts. * If a O2 sensor, wideband O2 sensor or A/F sensor has failed because of coolant contamination, do not replace the sensor until the leaky head gasket or cylinder head has been replaced. The new sensor will soon fail unless the coolant leak is fixed. * Some early Toyota applications with A/F sensors provide a "simulated" O2 sensor voltage to be displayed on a scan tool. The actual value was divided by 5 to comply with early OBD II regulations. Those regulations have since been revised, but be aware if you get a "funky" display on your scan tool
More Engine Sensor Articles: Oxygen Sensors: Diagnose & Replace Oxygen Sensor Locations Making Sense of Engine Sensors Air Temperature Sensors Coolant Sensors Crankshaft Position CKP Sensors MAP sensors Mass Airflow MAF Sensors Vane Airflow VAF Sensors http://www.aa1car.com/library/wraf.htm
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How Oxygen Sensors Affect Automotive Emissions
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How Oxygen Sensors Affect Automotive Emissions Copyright AA1Car Adapted from an article written by Larry Carley for Underhood Service magazine Oxygen sensors are a product that have been around for more than 20 years, yet most motorists do not even know they have one or more of these devices on their vehicle - let alone what it does. The only time most people even become aware of an oxygen sensor's existence is if they get a Check Engine light and there is a code that indicates an O2 sensor problem or their vehicle fails an emissions test because of a sluggish or dead O2 sensor. If their engine is not running well or is using too much fuel, somebody might tell them they might need a new O2 sensor. But in most cases, they will not have a clue as to how to diagnose or test this mysterious little device that is often blamed for all kinds of driveability and emissions ills. An O2 sensor monitors the fuel mixture so the engine computer (Powertrain Control Module) can adjust the air/fuel ratio to maintain the lowest possible emissions and best fuel economy. The O2 sensor does this by reacting to unburned oxygen in the exhaust. The sensor generates a small voltage signal (usually less than 1 volt) that increases when the air/fuel mixture goes rich, and drops when the air/fuel mixture goes lean. It acts like a rich/lean switch that signals the computer every time the fuel mixture changes, which is constantly. The computer maintains a balanced fuel mixture by doing the opposite of what the O2 sensor reads. If the O2 sensor reads rich (too much fuel), the computer shortens the on-time of each injector pulse to reduce the amount of fuel being squirted into the engine. This makes the mixture go lean. As soon as the O2 sensor detects this and gives a lean reading (not enough fuel), the computer reacts and increases the on-time of each injector pulse to add more fuel. This back-and-forth balancing act creates an average mixture that is pretty close to ideal. This is the "fuel feedback control loop" that allows today's vehicles to maintain extremely low emissions levels, and the O2 sensor is the key sensor in this loop. The computer uses other sensor inputs, too, like those from the coolant sensor, throttle position sensor, manifold absolute pressure sensor, airflow sensor, etc. to further refine the air/fuel radio as needed to suit changing operating conditions. But the O2 sensor provides the main input that determines what happens to the fuel mixture. So if the O2 sensor is not reading right, it screws up everything.
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How Oxygen Sensors Affect Automotive Emissions
Typically, a bad O2 sensor will read low (lean), which causes the engine to run too rich, pollute too much and use too much gas. A low reading can be caused by several things: old age, contamination, a bad wiring connection, or an ignition or compression problem in the engine. Getting Old As an O2 sensor ages, it does not react as quickly as it once did. The increased lag time makes the sensor sluggish and prevents the engine from keeping the air/fuel mixture in close balance. If the engine burns oil or develops an internal coolant leak, the sensor element may become contaminated causing the sensor to fail. Back when leaded gasoline was still available, a single tankful of leaded fuel would kill most O2 sensors in a few hundred miles. (That is a main reason why the government finally eliminated leaded fuel.) Because the sensor reacts to oxygen in the exhaust and not fuel, any engine problem that allows unburned air to pass through the cylinders will also trick an O2 sensor into reading lean. A misfiring spark plug or a leaky exhaust valve - even a leak in the exhaust manifold gasket - may allow enough air into the exhaust to screw up the sensor readings. It won't damage the sensor, but it will create a rich running condition that hurts emissions and fuel economy. Getting Hot Something else you need to know about O2 sensors is that they have to be hot (617 degrees to 662 degrees F) to produce a voltage signal. It may take a few minutes for the exhaust to heat up the sensor, so most O2 sensors in newer vehicles have a built-in electrical heater circuit to get the sensor up to temperature as quickly as possible. These are usually three-wire and four-wire O2 sensors. The single- and two-wire O2 sensors are unheated. If the heater circuit fails, it will not affect the operation of the O2 sensor once the exhaust gets hot but it will delay the computer from going into closed loop, which may cause a vehicle to fail an emissions test. Getting Checked Out O2 sensors can be diagnosed a variety of ways, most of which require special equipment. A scan tool or code reader is required to pull trouble codes from most newer vehicles, though manual "flash codes" are available on older vehicles (pre1995). If an O2 sensor problem is suspected, the sensor's response and voltage output can be monitored with a scan tool, a voltmeter or digital oscilloscope. If the tests confirm the O2 sensor is dead or sluggish, replacement is the only repair option. There is no way to "clean" or "rejuvenate" a bad O2 sensor. Note: Replacement sensors must be the same basic type as the original (heated or unheated) and have the same performance characteristics and heater wattage requirements. Installing the wrong O2 sensor could affect engine performance and possibly damage the heater control circuit in the engine computer. So make sure you follow the O2 sensor supplier's replacement listings. And do not go by appearance alone. Some replacement O2 sensors have an OEM-type wiring connection and require no modifications to install. Others (typically the "universal type O2 sensors") require splicing the sensor wires into the original connector harness. When To Replace Oxygen Sensors To maintain peak engine performance, there is no need to wait until the sensor fails to replace it. Some experts now recommend replacing O2 sensors at specific mileage intervals for preventive maintenance. The recommended interval for unheated one- or twowire O2 sensors on 1976 through early 1990s applications is every 30,000 to 50,000 miles. Heated three- and four-wire O2 sensors on mid-1980s through mid-1990s applications can be changed every 60,000 miles. And on 1996 and newer OBD II vehicles, the recommended replacement interval is 100,000 miles. Knowing What Type Is Used The most common zirconia type O2 units all work the same, but there are also titania O2 sensors and "wide-band" O2 sensors. Unheated zirconia O2 sensors are the oldest type. They have one or two wires and take up to several minutes to generate a signal after a cold start because they rely solely on the heat from the exhaust to reach normal operating temperature. Consequently, an unheated sensor may cool off at idle and stop producing a signal causing the engine control system to revert back to "open loop" operation (fixed air/fuel ratio setting). In 1982, heated zirconia O2 sensors appeared that added a special heater circuit inside the sensor to bring it up to operating temperature more quickly (in 30 to 60 seconds). This allows the engine to go into closed loop sooner, which reduces coldstart emissions. It also prevents the sensor from cooling off at idle. The heater requires a separate electrical circuit to supply voltage, so heated sensors usually have three or four wires.
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How Oxygen Sensors Affect Automotive Emissions
Titania O2 sensors use a different type of ceramic and produce a different kind of signal than zirconia type O2 sensors. Instead of generating a voltage signal that changes with the air/fuel ratio, the sensor's resistance changes and goes from low (less than 1,000 ohms) when the air/fuel ratio is rich to high (more than 20,000 ohms) when the air/fuel ratio is lean. The switching point occurs right at the ideal or stoichiometric air/fuel ratio. The engine computer supplies a base reference voltage (1 volt or 5 volts, depending on the application), and then reads the change in the sensor return voltage as the sensor's resistance changes. Titania O2 sensors are only used on a few applications, including some older Nissan and 19871990 Jeep Cherokee, Wrangler and Eagle Summit models. In 1997, some vehicle manufacturers began using a new type of O2 sensor. The heated planar O2 sensor has a flat, ceramic zirconia element rather than a thimble. The electrodes, conductive layer of ceramic, insulation and heater are all laminated together on a single strip. The new design works the same as the thimble-type zirconia sensors, but the "thick-film" construction makes it smaller, lighter and more resistant to contamination. The new heater element also requires less electrical power and brings the sensor up to operating temperature in only 10 seconds. Some new vehicles are also using a wide-band O2 sensor that is similar to the planar design but produces a higher voltage signal that changes in direct proportion to the air/fuel ratio (instead of switching back and forth like the other types of O2 sensors). This allows the engine computer to use an entirely different operating strategy to control the air/fuel ratio. Instead of switching the air/fuel ratio back and forth from rich to lean to create an average balanced mixture, it can simply add or subtract fuel as needed to maintain a steady ratio of 14.7:1.
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Related Articles: Understanding Oxygen (O2) Sensors Oxygen Sensor Locations Wideband Oxygen Sensors and Air/Fuel Sensors Understanding OBD II Driveability & Emissions Problems Fixing Emission Failures All About Onboard Diagnostics II (OBD II) Basic Emission Control Systems Overview Catalytic Converters Finding & Fixing Vacuum Leaks OBD II Emissions Testing Evolution of I/M 240
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Manifold Absolute Pressure MAP Sensors
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Manifold Absolute Pressure MAP Sensors Copyright AA1Car The Manifold Absolute Pressure (MAP) sensor is a key sensor because it senses engine load. The sensor generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment. When the engine is working hard, intake vacuum drops as the throttle opens wide. The engine sucks in more air, which requires more fuel to keep the air/fuel ratio in balance. In fact, when the computer reads a heavy load signal from the MAP sensor, it usually makes the fuel mixture go slightly richer than normal so the engine can produce more power. At the same time, the computer will retard (back off) ignition timing slightly to prevent detonation (spark knock) that can damage the engine and hurt performance. When conditions change and the vehicle is cruising along under light load, coasting or decelerating, less power is needed from the engine. The throttle is not open very wide or may be closed causing intake vacuum to increase. The MAP sensor senses this and the computer responds by leaning out the fuel mixture to reduce fuel consumption and advances ignition timing to squeeze a little more fuel economy out of the engine.
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Typical MAP sensor outputs for an older GM application.
HOW A MAP SENSOR WORKS MAP sensors are called manifold absolute pressure sensors rather than intake vacuum sensors because they measure the pressure (or lack thereof) inside the intake manifold. When the engine is not running, the pressure inside the intake manifold is the same as the outside barometric pressure. When the engine starts, vacuum is created inside the manifold by the pumping action of the pistons and the restriction created by the throttle plates. At full open throttle with the engine running, intake vacuum drops to almost zero and pressure inside the intake manifold once again nearly equals the outside barometric pressure. Barometric pressure typically varies from 28 to 31 inches of Mercury (Hg) depending on your location and climate conditions. Higher elevations have lower air pressure than areas next to the ocean or someplace like Death Valley, California, which is actually below sea level. In pounds per square inch, the atmosphere exerts 14.7 PSI at sea level on average. The vacuum inside an engine's intake manifold, by comparison, can range from zero up to 22 inches Hg or more depending on operating conditions. Vacuum at idle is always high and typically ranges from 16 to 20 inches Hg in most vehicles. The highest level of vacuum occurs when decelerating with the throttle closed. The pistons are trying to suck in air but the closed throttle chokes off the air supply creating a high vacuum inside the intake manifold (typically four to five inches Hg higher than at idle). When the throttle is suddenly opened, as when accelerating hard, the engine sucks in a big gulp of air and vacuum plummets to zero. Vacuum then slowly climbs back up as the throttle closes. When the ignition key is first turned on, the powertrain control module (PCM) looks at the MAP sensor reading before the engine starts to determine the atmospheric (barometric) pressure. So in effect, the MAP sensor can serve double duty as a BARO sensor. The PCM then uses this information to adjust the air/fuel mixture to compensate for changes in air pressure due to elevation and/or weather. Some vehicles use a separate "baro" sensor for this purpose, while others use a
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combination sensor that measures both called a BMAP sensor. On turbocharged and supercharged engines, the situation is a little more complicated because under boost there may actually be positive pressure in the intake manifold. But the MAP sensor doesn't care because it just monitors the absolute pressure inside the intake manifold. On engines with a "speed-density" electronic fuel injection system, airflow is estimated rather than measured directly with an airflow sensor. The computer looks at the MAP sensor signal along with engine rpm, throttle position, coolant temperature and ambient air temperature to estimate how much air is entering the engine. The computer may also take into account the oxygen sensor rich/lean signal and the position of the EGR valve, too, before making the required air/fuel mixture corrections to keep everything in balance. This approach to fuel management isn't as precise as systems that use a vane or mass airflow sensor to measure actual airflow, but it is not as complex or as costly either. Another advantage of speed-density EFI systems is that they are less sensitive to vacuum leaks. Any air that leaks into an engine on the back side an airflow sensor is "un-metered" air and really messes up the fine balance that's needed to maintain an accurate air/fuel mixture. In a speed-density system, the MAP sensor will detect the slight drop in vacuum caused by the air leak and the computer will compensate by adding more fuel. On many GM engines that have a mass airflow sensor (MAF), a MAP sensor is also used as a backup in case the airflow signal is lost, and to monitor the operation of the EGR valve. No change in the MAP sensor signal when the EGR valve is commanded to open would indicate a problem with the EGR system and set a fault code.
ANALOG MAP SENSORS The MAP sensor consists of two chambers separated by a flexible diaphragm. One chamber is the "reference air" (which may be sealed or vented to the outside air), and the other is the vacuum chamber which is connected to the intake manifold on the engine by a rubber hose or direct connection. The MAP sensor may be mounted on the firewall, inner fender or intake manifold. A pressure sensitive electronic circuit inside the MAP sensor monitors the movement of the diaphragm and generates a voltage signal that changes in proportion to pressure. This produces an analog voltage signal that typically ranges from 1 to 5 volts. Analog MAP sensors have a three-wire connector: ground, a 5-volt reference signal from the computer and the return signal. The output voltage usually increases when the throttle is opened and vacuum drops. A MAP sensor that reads 1 or 2 volts at idle may read 4.5 volts to 5 volts at wide open throttle. Output generally changes about 0.7 to 1.0 volts for every 5 inches Hg of change in vacuum.
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FORD DIGITAL MAP SENSORS Ford BP/MAP sensors (barometric pressure/manifold absolute pressure) also measure load but produce a digital frequency signal rather than an analog voltage signal. This type of sensor has additional circuitry that creates a 5 volt "square wave" (on-off) voltage signal. The signal increases in frequency as vacuum drops. At idle or when decelerating, vacuum is high and the BP/MAP sensor output may drop to 100 Hz (Hertz, or cycles per second) or less. At wide open throttle when there is almost no vacuum in the intake manifold, the sensor's output may jump to 150 Hz or higher. At zero vacuum (atmospheric pressure), a Ford BP/MAP sensor should read 159 Hz.
MAP SENSOR DRIVABILITY SYMPTOMS Anything that interferes with the MAP sensor's ability to monitor the pressure differential may upset the fuel mixture and ignition timing. This includes a problem with the MAP sensor itself, grounds or opens in the sensor wiring circuit, and/or vacuum leaks in the intake manifold (airflow sensor systems) or hose that connects the sensor to the engine. Typical driveability symptoms that may be MAP related include: * Surging. * Rough idle. * A rich fuel condition, which may cause spark plug fouling. * Detonation due to too much spark advance and a lean fuel ratio. * Loss of power and/or fuel economy due to retarded timing and an excessively rich fuel ratio. A vacuum leak will reduce intake vacuum and cause the MAP sensor to indicate a higher than normal load on the engine. The computer will try to compensate by richening the fuel mixture and retarding timing -- which hurts fuel economy, performance and emissions.
MAP SENSOR CHECKS First, make sure engine manifold vacuum is within specifications at idle. If vacuum is unusually low due to a vacuum leak, retarded ignition timing, an exhaust restriction (clogged converter), or an EGR leak (EGR valve not closing at idle). A low intake vacuum reading or excessive backpressure in the exhaust system can trick the MAP sensor into indicating there is a load on the engine. This may result in a rich fuel condition. A restriction in the air intake (such as a plugged air filter), on the other hand, may produce higher than normal vacuum
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readings. This would result in a load low indication from the MAP sensor and possibly a lean fuel condition. A good MAP sensor should read barometric air pressure when the key is turned on before the engine starts. This value can be read on a scan tool and should be compared to the actual barometric pressure reading to see if they match. Your local weather channel or website should be able to tell you the current barometric pressure reading. Check the sensor's vacuum hose for kinks or leaks. Then use a hand-held vacuum pump to check the sensor itself for leaks. The sensor should hold vacuum. Any leakage calls for replacement. An outright failure of the MAP sensor, loss of the sensor signal due to a wiring problem, or a sensor signal that is outside the normal voltage or frequency range will usually set a diagnostic trouble code (DTC) and turn on the Check Engine light.
MAP SENSOR SCAN TOOL CHECKS On 1995 and newer vehicles with OBD II self-diagnostics, a DTC code P0105 to P0109 would indicate a fault in the MAP sensor circuit. P0105....Manifold Absolute Pressure/Barometric Pressure Circuit P0106....Manifold Absolute Pressure/Baro Pressure out of range P0107....Manifold Absolute Pressure/Baro Pressure Low Input P0108....Manifold Absolute Pressure/Baro Pressure High Input P0109....Manifold Absolute Pressure/Baro Pressure Circuit Intermittent On older pre-OBD II vehicles, the MAP codes are: * General Motors: Codes 34, 33, 31 * Ford: Codes 22, 72 * Chrysler: Codes 13, 14 On vehicles that provide data stream through a diagnostic connector and allow a scan tool to display sensor values, the MAP sensor's output voltage can be read and compared to specifications. Basically, you want to see a quick and dramatic change in the MAP sensor signal when the throttle on an idling engine is snapped open and shut. No change would indicate a sensor or wiring fault. If the sensor is reading low or there is no reading at all, check for proper reference voltage to the sensor. It should be very close to 5 volts. Also check the ground connection. If the reference voltage is low, check the wiring harness and connector for looseness, damage or corrosion. Scan tools that display OBD II data will also display a "calculated load value" that can be used to determine if the MAP sensor is working or not. The load value is computed using inputs from the MAP sensor, TPS sensor, airflow sensor and engine speed. The value should be low at idle, and high when the engine is under load. No change in the value, or a higher than normal reading at idle might indicate a problem with the MAP sensor, TPS sensor or airflow sensor.
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If you display the MAP sensor output on a Digital Storage Oscilloscope (DSO), this is what the waveform might look lik e as the throttle position, engine load and speed change.
MAP SENSOR TESTS A MAP sensor can also be bench tested by applying vacuum to the vacuum port with a hand vacuum pump. With 5 volts to the reference wire, the output voltage of an analog MAP sensor should drop, and on a Ford digital MAP sensor the frequency should increase. An analog MAP sensor's voltage can also be read directly using a voltmeter or oscilloscope. A digital MAP sensor's frequency signal can be read with a DVOM if it has a frequency function, or an oscilloscope. The leads would be connected to the signal wire and ground. Warning: Do NOT use an ordinary voltmeter to check a Ford BP/MAP sensor because doing so can damage the electronics inside the sensor. This type of sensor can only be diagnosed with a DVOM that displays frequency, or a scope or scan tool. Another way to check out a Ford digital MAP sensor circuit is to input a "simulated" MAP sensor signal with a tester that can generate an adjustable frequency signal. Changing the frequency of the simulated signal should trick the computer into changing the fuel mixture (look for a change in the injector pulse width signal). No change would indicate a possible computer problem.
MAP SENSOR REPLACEMENT If a MAP sensor needs to be replaced, make sure the replacement is the correct one for the application. Differences in calibration between model years and engines will affect the operation of the engine management system. If a vehicle is more than five years old, the vacuum hose that connects the MAP sensor to the engine should also be replaced.
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Mass Airflow MAF Sensors
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Mass Airflow MAF Sensors Copyright AA1Car Mass airflow sensors (MAF), which are used on a variety of multiport fuel injection systems, come in two basic varieties: hot wire and hot film. Though slightly different in design, both types of sensors measure the volume and density of the air entering the engine so the computer can calculate how much fuel is needed to maintain the correct fuel mixture. Mass airflow sensors have no moving parts. Unlike a vane airflow meter that uses a spring-loaded flap, mass airflow sensors use electrical current to measure airflow. The sensing element, which is either a platinum wire (hot wire) or nickel foil grid (hot film), is heated electrically to keep it a certain number of degrees hotter than the incoming air. In the case of hot film MAFs, the grid is heated to 75 degrees C. above incoming ambient air temperature. With the hot wire sensors, the wire is heated to 100 degrees C. above ambient temperature. As air flows past the sensing element, it cools the element and increases the current needed to keep the element hot. Because the cooling effect varies directly with the temperature, density and humidity
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Mass Airflow MAF Sensors
of the incoming air, the amount of current needed to keep the element hot is directly proportional to the air "mass" entering the engine. MASS AIRFLOW SENSOR OUTPUT MAF sensor output to the computer depends on the type of sensor used. The hot wire version, which Bosch introduced back in '79 on its LH-Jetronic fuel injection systems and is used on a number of multiport systems including GM's 5.0L and 5.7L Tuned Port Injection (TPI) engines, generates an analog voltage signal that varies from 0 to 5 volts. Output at idle is usually 0.4 to 0.8 volts increasing up to 4.5 to 5.0 volts at wide open throttle. The hot film MAFs, which AC Delco introduced in '84 on the Buick turbo V6 and have since used on the 2.8, 3.0 and 3.8L V6 engines, produce a square wave variable frequency output. The frequency range varies from 30 to 150 Hz, with 30 Hz being average for idle and 150 Hz for wide open throttle.
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Another difference between the hot wire and hot film sensors is that the Bosch hot wire units have a self-cleaning cycle where the platinum wire is heated to 1000 degrees C. for one second after the engine is shut down. The momentary surge in current is controlled by the onboard computer through a relay to burn off contaminants that might otherwise foul the wire and interfere with the sensor's ability to read incoming air mass accurately.
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Mass Airflow MAF Sensors
MASS AIRFLOW SENSOR DIAGNOSTIC FAULT CODES An engine with a bad MAF sensor may start and stall or be hard to start, it may hesitate under load, idle rough or run excessively rich or lean. The engine may also hiccup when the throttle suddenly changes position. Often, a dirty or faulty MAF sensor will cause the engine to set a LEAN code and turn on the Check Engine Light. If the MAF sensor wire becomes dirty or is contaminated with oil (from an aftermarket reusable air filter), it will be slow to react to changes in airflow. This may cause the MAF sensor to under-report airflow, causing the engine to run lean. On OBD II vehicles, the input from the MAF sensor is combined with those form the throttle position sensor, MAP sensor and engine speed to calculate engine load. If your scan tool can display calculated engine load, look at the value to see if the load is low at idle, and higher when the engine is running under load. No change in the reading or a reading that makes no sense could indicate a problem with any of these sensors. If you suspect a MAF sensor problem, scan for any fault codes. Trouble codes that may indicate a problem with the mass airflow sensor include: P0100....Mass or Volume Air Flow Circuit P0101....Mass or Volume Air Flow Circuit Range/Performance Problem P0102....Mass or Volume Air Flow Circuit Low Input P0103....Mass or Volume Air Flow Circuit High Input P0104....Mass or Volume Air Flow Circuit Intermittent P0171....System too Lean (Bank 1) P0172....System too Rich (Bank 1) P0173....Fuel Trim Malfunction (Bank 2) P0174....System too Lean (Bank 2) P0175....System too Rich (Bank 2) On older Pre-OBD II vehicles, you can use a scan tool or manual flash code procedure to read the codes: GM Pre-OBD II: Code 33 (too high frequency) and Code 34 (too low frequency) on engines with multiport fuel injection only, and Code 36 on 5.0L and 5.7L engines that use the Bosch hot wire MAF if the burn-off cycle after shut-down fails to occur. Ford Pre-OBD II: Code 26 (MAF out of range), Code 56 (MAF output too high), Code 66 (MAF output too low), and Code 76 (no MAF change during "goose" test). Of course, don't overlook the basics, too such as engine compression, vacuum, fuel pressure, ignition, etc., since problems in any of these areas can produce similar driveability symptoms. MASS AIRFLOW SENSOR DIAGNOSIS Unlike vane airflow meters with their movable flaps, MAFs have no moving parts so the only way to know if the unit is functioning properly is to look at the sensor's output, or its effect on injector timing.
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With the Bosch hot wire sensors, sensor voltage output can be read directly with a digital voltmeter by probing the appropriate terminals. If the voltage readings are out of range, or if the sensor's voltage output fails to increase when the throttle is opened with the engine running, the sensor is defective and needs to be replaced. A dirty wire (which may be the result of a defective self-cleaning circuit or external contamination of the wire) can make the sensor slow to respond to changes in airflow. A broken or burned out wire would obviously prevent the sensor from working at all. Power to the MAF sensor is provided through a pair of relays (one for power, one for the burn-off cleaning cycle), so check the relays first if the MAF sensor appears to be dead or sluggish. On GM MAF sensors, there are a couple of quick checks you can do for vibration-related sensor problems. Attach an analog voltmeter to the appropriate MAF sensor output terminal. With the engine idling, the sensor should be putting out a steady 2.5 volts. Tap lightly on the sensor and note the meter reading. A good sensor should show no change. If the analog needle jumps and/or the engine momentarily misfires, the sensor is bad and needs to be replaced. You can also check for heatrelated problems by heating the sensor with a hair dryer and repeating the test. This same test can also be done using a meter that reads frequency. The older AC Delco MAF sensors (like a 2.8L V6) should show a steady reading of 30 to 50 Hz at idle and 70 to 75 Hz at 3,500 rpm. The later model units (like those on a 3800 V6) should read about 2.9 kHz at idle and 5.0 kHz at 3,500 rpm. If tapping on the MAF sensor produces a sudden change in the frequency signal, it's time for a new sensor. On the GM hot film MAFs, you can also tap into the onboard computer data stream with a scan tool to read the MAF sensor output in "grams per second" (GPS). The reading might go from 3 to 5 GPS at idle up to 100 to 240 GPS at wide open throttle and 5000 RPM. The scantool GPS reading at idle will vary by engine displacement. The larger the engine, the higher the GPS reading at idle. The GPS idle reading will roughly correspond to engine displacement in liters. A 3.0L V6 engine, for example, will generate a GPS reading of about 3.0 grams per second at idle. A larger 5.0L V8 would read around 5 grams per second, and a smaller 2.0L four cylinder would read around 2 grams per second at idle. Some vehicle manufacturers publish MAF sensor GPS reading specifications for specific engine speeds. The engine is held steady at the specified RPM to compare the scantool GPS reading to the spec. If the reading is off by more than 10 percent, the MAF sensor is not reading airflow correctly. The cause could be a dirty sensor that needs to be cleaned.
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Mass Airflow MAF Sensors
Like throttle position sensors, there should be smooth linear transition in sensor output throughout the rpm range. If the readings jump all over the place, the computer won't be able to deliver the right air/fuel mixture and driveability and emissions will suffer. So you should also check the sensor's output at various speeds to see that it's output changes appropriately. This can be done by graphing its frequency output every 500 rpm, or by observing the sensor's waveform on a scope. The waveform should be square and show a gradual increase in frequency as engine speed and load increase. Any skips or sudden jumps or excessive noise in the pattern would tell you the sensor needs to be replaced. Another way to check MAF sensor output is to see what effect it is has on injector timing. Using an oscilloscope or multimeter that reads milliseconds, connect the test probe to any injector ground terminal (one injector terminal is the supply voltage and the other is the ground circuit to the computer that controls timing). Then look at the duration of the injector pulses at idle (or while cranking the engine if the engine won't start). Injector timing varies depending on the application, but if the mass airflow sensor is not producing a signal, injector timing will be about four times longer than normal (possibly making the fuel mixture too rich to start). You can also use millisecond readings to confirm fuel enrichment when the throttle is opened during acceleration, fuel leaning during light load cruising and injector shut-down during deceleration. Under light load cruise, for example, you should see about 2.5 to 2.8 Ms duration.
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Mass Airflow MAF Sensors
CLEANING FORD MAF SENSORS For some reason, Ford vehicles have had a history of MAF sensor problems caused by contamination. In some cases, dirt gets past a leaky air filter and fouls the sensor wire. In other cases, carbon varnish builds up on the sensor from fuel vapors backing up through the intake manifold. Either way, contamination makes the MAF sensor sluggish, and often sets a P0171 or P0174 lean code. The fix is to clean the sensor element with aerosol electronics cleaner (CRC makes a good product for this). The MAF sensor is located inside the air filter housing on some applications (Windstar, for example) or between the air filter and throttle body. Spray the sensor element with electronics cleaner, let it soak for about 10 minutes, then repeat. DO NOT use any other type of cleaner as this may damage the sensor. Also, DO NOT touch, scrub or attempt to physically clean the sensor element as this too can ruin the sensor.
Repeat GM MAF Sensor Failures Blamed on Engine Backfires GM says that repeated instances of Mass Air Flow (MAF) sensor failure on some of their vehicles may be due to engine backfires. The sudden buildup of pressure inside the intake manifold that results from a backfire can crack the heated element inside the MAF sensor causing it to fail. Common causes of engine backfire include a lean misfire due to low fuel pressure or restricted fuel injectors, breakdown of the secondary ignition including internal ignition coil arcing, and a dead spot in the Throttle Position Sensor (TPS). A lean fuel condition can be verified by using a scan tool to monitor the Block Learn memory value with the engine at a steady no load cruise rpm. A reading above the 135 to 140 range would indicate a lean fuel mixture, or an air leak in the exhaust manifold ahead of the oxygen sensor. Internal ignition coil arcing between the coil primary and secondary windings can be very difficult to trace. Checking for internal coil arcing requires a professional level engine analyzer/scope. A dead spot in the TPS can be verified by monitoring the sensor voltage as the throttle is moved from the idle position to the Wide Open Throttle position (very slowly) with an analog voltmeter or a digital storage oscilloscope or scan tool with graphing capability.
Troubleshooting GM Mass Airflow Sensor Video: The following video is courtesy Wells Manufacturing via YouTube.
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Vane Airflow VAF Sensor
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Vane Airflow VAF Sensors Copyright AA1Car
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Airflow sensors are used on engines with multiport electronic fuel injection. This is because the amount of fuel delivered by an EFI system is controlled by a computer (powertrain control module or PCM) which turns the fuel injectors on and off. The airflow sensor keeps the computer informed about how much air is being pulled into the engine past the throttle plates. This input along with information from other engine sensors allows the computer to calculate how much fuel is needed. The computer then increases or decreases injector duration (on time) to provide the correct air/fuel ratio. On engines equipped with Throttle Body Injection (TBI) or a Speed-Density type of EFI system (most Chryslers and some GM applications), air flow is not measured directly but is estimated using inputs from the throttle position, manifold air temperature and manifold absolute pressure (MAP) sensors. But on engines with airflow EFI systems, airflow is measured directly by a vane airflow (VAF) sensor, a mass airflow sensor, or on some Japanese applications, a "Karman-Vortex" airflow sensor. VANE AIRFLOW APPLICATIONS Vane airflow sensors (also called airflow meters) are found mostly on German imports equipped with Bosch L-Jetronic fuel injection, Japanese imports equipped with Nippondenso multiport electronic fuel injection (made under Bosch license), and Ford vehicles equipped with the Bosch multiport EFI (such as Escort/Lynx, Turbo T-Bird and Mustang with the 2.3L turbo engine, Ford Probe with the 2.2L engine), and various other makes and models of vehicles.
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Vane Airflow VAF Sensor
HOW A VANE AIRFLOW SENSOR WORKS A vane airflow sensor is located ahead of the throttle and monitors the volume of air entering the engine by means of a spring-loaded mechanical flap. The flap is pushed open by an amount that is proportional to the volume of air entering the engine. The flap has a wiper arm that rotates against a sealed potentiometer (variable resistor or rheostat), allowing the sensor's resistance and output voltage to change according to airflow. The greater the airflow, the further the flap is forced open. This lowers the potentiometer's resistance and increases the voltage return signal to the computer. The vane airflow sensor also contains a safety switch for the electric fuel pump relay. Airflow into the engine activates the pump. So if the engine won't start because the fuel pump won't kick in, the problem may be in the airflow sensor. The easiest to check the safety switch is to turn the ignition key on and push the flap open. If the fuel pump does not come on, the contact inside the sensor is probably defective. A sealed idle mixture screw is also located on the airflow sensor. This controls the amount of air that bypasses the flap, and consequently the richness or leanness of the fuel mixture. VANE AIRFLOW SENSOR PROBLEMS Vane airflow sensors as well as all the other types of airflow sensors can't tolerate air leaks. Air leaks downstream of the sensor can allow "unmetered" or "false" air to enter the engine. The extra air can lean out the fuel mixture causing a variety of driveability problems, including lean misfire, hesitation and stumbling when accelerating, and a rough idle. Dirt can also cause problems. Unfiltered air passing through a torn or poor fitting air filter can allow dirt to build up on the flap shaft of a vane airflow sensor causing the flap to bind or stick. The operation of the flap can be tested by gently pushing it open with a finger. It should open and close smoothly with even resistance. If it binds or sticks, a shot of carburetor cleaner may loosen it up otherwise the sensor will have to be replaced. Backfiring in the intake manifold can force the flap backwards violently, often bending or breaking the flap. Some sensors have a "backfire" valve built into the flap to protect the flap in case of a backfire by venting the explosion. But the antibackfire valve itself can become a source of trouble if it leaks. A leaky backfire valve will cause the sensor to read low and the engine to run rich. VANE AIRFLOW SENSOR DIAGNOSIS For Bosch applications, there is a special Bosch tester to check the output of the sensor. But a technician can also check a vane airflow sensor by using a multimeter to check the voltage and resistance values between the sensor's various terminals. As a rule, the sensor's output voltage should rise from around 0.25 volts up to about 4.5 volts as the flap goes from closed to open. If the voltage reading is low, the reference voltage from the computer (VRef) should also be checked (it should be 5 volts on most applications).
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Watching a vane airflow sensor's output on a digital storage oscilloscope (DSO) is a good way to detect "skips" or dead spots in the sensor's internal potentiometer. A good sensor should produce a smooth and gradual voltage transition from idle to wide open throttle. Changes in the sensor's voltage output should also produce a corresponding change in fuel injector duration when the engine is running. Injector duration should increase as the VAF flap is pushed open. The rheostat that senses the position of the air flap most often becomes worn in the positioin just above idle to about 20% throttle. This is where most problems are likely to occur. Vane airflow sensors are not serviceable, so must be replaced if there are any internal problems with the unit. We�ve heard of people taking the sensor housing apart and using electronics cleaner to clean the rheostat contacts. This may restore normal operation if the contacts are not worn, but it would be no help if the sensor has an electronic fault or a damaged flap.
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More Sensor Related Articles: Making Sense of Engine Sensors Air Temperature Sensors Coolant Sensors Crankshaft Position CKP Sensors MAP sensors Throttle Position Sensors Mass Airflow MAF sensors Oxygen Sensors Wide Ratio Air Fuel (WRAF) Sensors Understanding Engine Management Systems Powertrain control modules (PCMs) Flash Reprogramming PCMs All About Onboard Diagnostics II (OBD II) Zeroing in on OBD II Diagnostics Controller Area Network (CAN) Diagnostics
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Engine Throttle Position Sensors
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Engine Throttle Position Sensor Copyright AA1Car Late model engines with feedback carburetion or electronic fuel injection use a "Throttle Position Sensor" (TPS) to inform the computer about the rate of throttle opening and relative throttle position. A separate idle switch (sometimes called a "Nose" switch) and/or wide open throttle (WOT) switch may also be used to signal the computer when these throttle positions exist. The throttle position sensor may be mounted externally on the throttle shaft as is the case on most fuel injection throttle bodies, or internally in the carburetor as it is in the Rochester Varajet, Dualjet and Quadrajet. The TPS is essentially a variable resistor that changes resistance as the throttle opens. Think of it as the electronic equivalent of a mechanical accelerator pump. By signaling the computer when the throttle opens, the computer can richen up the fuel mixture to maintain the proper air/fuel ratio. The initial setting of the TPS is critical because the voltage signal the computer receives back from the TPS tells the computer the exact position of the throttle. The initial adjustment, therefore, must be set as closely as possible to the factory specs. Most specs are given to the nearest hundredth of a volt! And since there is no range of "acceptable" specs given for a specific application, the TPS should be adjusted as closely as possible to those in the manual. This is accomplished by reading the TPS voltage at a specific throttle position using a 10k ohm impedance digital voltmeter, or on GM vehicles, using a hand-held scan tool that plugs into the vehicle diagnostic connector.
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The TPS sensor monitors throttle position. TPS ON DRIVE-BY-WIRE CARS Most late model cars and trucks have no throttle cable. A small electric motor is used to operate the throttle using inputs from position sensors on the gas pedal. When the gas pedal is depressed, the electrical resistance of the potentiometers inside the pedal sensors change. The control module notes the change in position and commands the throttle to open. A pair of throttle position sensors on the throttle shaft note the change in throttle position and provide feedback signals to the control module so the module knows the exact position of the throttle and that everything is working correctly. DRIVABILITY SYMPTOMS The classic symptom of a defective or misadjusted TPS is hesitation or stumble during acceleration (in other words, the same symptoms a bad accelerator pump would produce). The fuel mixture leans out because the computer doesn't receive the right signal telling it to add fuel as the throttle opens. The oxygen sensor feedback circuit will eventually provide the necessary information, but not quickly enough to prevent the engine from stumbling. Throttle position sensors typically experience the most wear in the position just above idle, since this is the throttle's position for most driving. A worn sensor may cause a skip or drop in the reading when the throttle opens, causing a momentary loss of input to the PCM. The result is usually a hesitation or stumble because the PCM fails to provide the necessary fuel enrichment. If the TPS mounting is loose, it will produce an erratic signal leading the ECM to believe the throttle is opening and closing. The result can be an unstable idle and intermittent hesitation. If the TPS is shorted, the computer will receive the equivalent of a wide open throttle signal all the time. This will make the fuel mixture run rich and set a fault code that corresponds to a voltage signal that's too high. If the TPS is open, the computer will think the throttle is closed all the time. The resulting fuel mixture will be too lean and a fault code that corresponds to a voltage signal that's too low will be set. SENSOR CHECKS First, check for the presence of any fault codes. Codes that may indicate TPS problems include: P0120....Throttle/Pedal Position Sensor/Switch A Circuit P0121....Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Problem P0122....Throttle/Pedal Position Sensor/Switch A Circuit Low Input P0123....Throttle/Pedal Position Sensor/Switch A Circuit High Input P0124....Throttle/Pedal Position Sensor/Switch A Circuit Intermittent P0220....Throttle/Pedal Position Sensor/Switch 'B' Circuit P0221....Throttle/Pedal Position Sensor/Switch 'B' Circuit Range/Performance Problem
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P0222....Throttle/Pedal Position Sensor/Switch 'B' Circuit Low Input P0223....Throttle/Pedal Position Sensor/Switch 'B' Circuit High Input P0224....Throttle/Pedal Position Sensor/Switch 'B' Circuit Intermittent P0225....Throttle/Pedal Position Sensor/Switch 'C' Circuit P0226....Throttle/Pedal Position Sensor/Switch 'C' Circuit Range/Performance Problem P0227....Throttle/Pedal Position Sensor/Switch 'C' Circuit Low Input P0228....Throttle/Pedal Position Sensor/Switch 'C' Circuit High Input P0229....Throttle/Pedal Position Sensor/Switch 'C' Circuit Intermittent On older pre-OBD II vehicles, the codes for the throttle position sensor include: * General Motors Pre-OBD II: 21, 22 * Ford (EEC-IV) Pre-OBD II: 23, 53, 63, 73 * Chrysler Pre-OBD II: 24 If you find a code, then refer to the appropriate diagnostic chart and follow the step-by-step checks to isolate the cause. If you don't find any codes, you can still do the following scan tool and voltage checks.
SCAN TOOL CHECKS A scan tool that can display sensor data will usually show the throttle position as a percentage of opening. Professional grade scan tools may also be able to display the TPS sensor's actual voltage, depending on the software. Plug the scan tool into the vehicle's diagnostic connector, turn the key ON, and note the throttle opening reading. At idle is should be zero or a couple of degrees. Press down on the gas pedal very S-L-O-W-L-Y until the throttle is all the way open. You should see the percentage of throttle opening gradually increase to 100 percent at wide open throttle. No change in the scan tool reading would indicate no input from the throttle position sensor. Or, if you see more than 5 percent open at idle, or less than 90% open at WOT, it could indicate a problem with the sensor. Note: Most scan tools do not update their readings quickly enough to detect a momentary glitch in the TPS reading during a TPS sweep from idle to WOT. If the TPS has a worn spot, most likely it will be between 0 and 20 percent throttle opening. Try holding the throttle between 0 and 20 percent to see if you get a steady reading. If the reading suddenly drops while holding the gas pedal or throttle linkage steady, it may indicate a fault with the sensor.
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TPS VOLTAGE CHECKS If your scan tool cannot display a voltage value for the TPS, you can measure the sensor's output voltage by packprobing the sensor conenctor with a voltmeter. First, check for the presence of voltage at the TPS with the key on. The TPS cannot deliver the proper signal if it does not receive reference voltage from the computer. Refer to a wiring diagram for the reference connection and look for 5 volts. The second check is the base voltage reading. Compare the voltage reading to the manual specifications. TPS voltage values are often specified to the nearest hundredth of a volt, so if the base TPS voltage reading is not within .05 volts of the specified value, adjustment may be needed (if it is adjustable). If it is not adjustable and the reading is out of specifications, replace the sensor. The third check is for the proper voltage change as the throttle opens and closes. Voltage should rise smoothly from about 1 volt to a maximum of 5 volts at wide open throttle. No voltage rise or skips in the reading means the sensor needs to be replaced. Observing the sensor's output signal as a trace on an oscilloscope can be a real time-save here because it is easy to see any deviations in the voltage curve.
TPS ADJUSTMENT Under normal circumstances, a TPS should not require adjustment. But if your diagnosis reveals a problem with the TPS voltage setting, if the TPS is defective and must be replaced or if the carburetor or throttle body is replaced, then adjustment http://www.aa1car.com/library/tps_sensors.htm
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may be required. Note: This applies to older vehicles only. On most late model vehicles, the TPS is self-calibrating. The engine computer uses the base voltage reading at idle as representing 0% throttle opening. NOTE: The TPS on most remanufactured carburetors is preset at the factory to an "average" setting for the majority of applications the carb fits. Even so, the TPS should be reset to the specific application upon which it is installed. Through 1982, all GM throttle position sensors were adjustable. But on newer applications, many sensors are not adjustable. Starting in 1984, for example, GM went to a nonadjustable TPS on the 1.8 and 2.5L Pontiac engines. Likewise, Chevy switched to a nonadjustable TPS starting in '85 on the 2.0L engine. On engines with a nonadjustable TPS, the ECM uses whatever idle reading it gets from the TPS as the base voltage reference point. With adjustable TPS sensors, the adjustment procedure will vary depending on the application. On Rochester carburetors with an internal TPS, it involves removing an antitamper plug on top of the carburetor. On some fuel injected applications, the throttle body must be removed to drill out welds that hold the TPS screws. With externally mounted throttle position sensors, the sensor is adjusted by loosening the mounting screws (or drilling out the mounting rivets) and rotating the sensor slightly one way or the other until the desired voltage reading is obtained. The basic adjustment procedures goes as follows: 1. Remove the anti-tampering plug (if applicable) or loosen the mounting screws or remove the rivets holding the TPS. 2. Refer to the electrical diagram in a manual to determine which connectors are used to make the TPS reading. On the Rochester carbs, for example, use the TPS center terminal "B" and bottom terminal "C." If the vehicle provides access to TPS data stream, use a scan tool to read the sensor's output by plugging into the diagnostic connector. 3. Turn the ignition on. Adjust the TPS with the throttle in the specified position (idle, high step of fast idle cam or resting against the throttle stop screw with the ISC plunger fully retracted) until the proper voltage reading is obtained.
News Update: June 2011
New Non-Contact TPS Sensors For Replacing Worn Original Equipment Sensors Airtex Engine Management has introduced a line of advanced non-contact-design throttle position sensors that eliminate the premature wear and common drivability issues experienced with conventional Throttle Position Sensors. The new Airtex throttle position sensors are now available for many mid-1980s through 2007 Dodge, Ford, General Motors and Mazda applications. Conventional original equipment and replacement throttle position sensors have metal contact fingers that sweep across a printed resistor board to indicate throttle position. Repetitive motion and vehicle vibration can cause these fingers to wear holes in the board, causing dead spots that result in engine hesitation and other drivability problems. The new Airtex sensors utilize advanced Hall Effect integrated circuitry that eliminates wear-intensive contact with the circuit board. This technology until now has not been widely available in the aftermarket, in spite of its significant advantages over conventional throttle position sensor designs. For more information, visit Airtex Engine Management.
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More Engine Sensor Articles: Throttle-By-Wire systems (Electronic Throttle Control)
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How to Read Diagnostic Trouble Codes
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How to Read Diagnostic Trouble Codes Copyright AA1Car Check Engine Light On? That means the onboard diagnostic system on your vehicle has detected a problem that could increase emissions. When this happens, the OBD II system sets one or more diagnostic trouble codes that correspond to the problem detected. To read the codes, you will have to plug a scan tool or code reader into the 16-pin OBD II diagnostic connector, which is usually located under the dash near the steering column. The tool will then display the code or codes that have turned on the Check Engine Light. To read codes, you need the proper scan tool. On older (pre-1996) vehicles, an OBD I scan tool is required. Since connectors were not standardized, the scan tool must have the proper adapter for the vehicle's diagnostic connector (since they were all different). On 1996 and newer vehicles is OBD II, the connectors are all the same - but the software (and hardware) that is required to read the codes can vary depending on the year, make and model of your vehicle. For more information about different types of scan tools, Click Here
HOW TO READ DIAGNOSTIC TROUBLE CODES 1. Locate the 16-pin OBD II diagnostic connector (usually under the dash near the steering column). Note: On some vehicles, it may be necessary to remove a knee bolster panel or other panel to find the connector. On some the connector may be located in the center console or someplace else. If you cannot locate the OBD II diagnostic connector, refer to your vehicle owners manual. 2. Plug in your code reader or scan tool. 3. Turn the ignition ON, but do not start the engine. This is usually necessary so the scan tool can communicate with your car's computer. 4. Depending on the scan tool you are using, push the READ CODES button or select the READ CODES option on the tool
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menu. Note: some scan tools do not automatically recognize the year, make and mode of your vehicle. You will first have to enter this information before the scan tool will read any fault codes. 5. Your scan tool should display any diagnostic fault codes that are present in numerical order. WRITE DOWN THE CODES! This is important for later reference. If your tool does not also display the definition of the code, Click Here to look up the definition of the code(s). 6. You can no safety clear (erase) the codes by pressing the CLEAR CODES button or choosing the erase code option on the scan tool menu. 7. VERY IMPORTANT: Most codes DO NOT tell you what part to replace,only that a problem has occurred in a particular sensor circuit or system. Further diagnostics will usually be necessary to diagnose the faulty part that needs to be replaced to fix your problem. 8. Clearing the codes does NOT make the problem go away. If the problem is still present, sooner or later the Check Engine Light will come back on the the same code(s) will reset.
CHECK ENGINE LIGHT The "Malfunction Indicator Lamp" (or Check Engine Light as most people call it) is supposed to come on when a problem occurs in the engine control system that affects emissions. Depending on how the system is configured and the nature of the problem, the lamp may come on and go off, remain on continuously or flash. Some types of intermittent problems will make the lamp come on only while the fault is occurring. When the problem goes away, the lamp goes off. Other types of problems will turn the light on, and it will remain on until the fault is diagnosed and repaired. The Check Engine lamp has proven to be a great annoyance to many motorists (as well as your professional customers) because it doesn't tell you anything about the nature of the problem. The problem could be something serious or relatively minor. There is no way to know until you hook up a scan tool and read out the code(s) that caused the light to come on. If the engine seems to be running normally, and no other warning lights are on, you can probably ignore the light and keep driving. But you should read the codes as soon as possible to find out what is going on. Also, if you live in an area that requires vehicle emissions testing, you vehicle will NOT pass an emissions test if the Check Engine Light is on or there are any live trouble codes in memory.
Clearing Trouble Codes In most of the first generation onboard diagnostic systems prior to OBD II, disconnecting the computer's power source or disconnecting a battery cable could erase fault codes. The loss of voltage wiped out the computer's temporary memory causing the Check Engine light to magically go out. But as soon as the original problem reoccurred, the code(s) would be reset and the light would come back on. In most newer computer systems, fault codes are stored in a "nonvolatile" memory that is not lost if the battery is disconnected. The codes remain intact until they are cleared using a scan tool (which few motorists own). What's more, disconnecting the battery or computer's power supply can have undesirable consequences because it causes the loss of electronic presets in the radio and climate control system, as well as the engine computer's "learned" memory - the adjustments that are made over time to compensate for engine wear and driving habits. On some vehicles where the computer also regulates the electronic transmission, the computer may have to be put through a special learning procedure to relearn the proper operation of the transmission if power has been lost!
HOW OBD II SETS TROUBLE CODES Prior to OBD II, fault detection was mostly limited to "gross failures" within individual circuits or sensors. The first generation systems couldn't detect engine misfire, how well the catalytic converter was functioning or whether a vehicle was leaking fuel vapors into the atmosphere. OBD II changed all of that by adding the ability to monitor these things so emission problems can be detected as they develop. OBD II still uses the Check Engine lamp to alert the driver when a fault occurs, and it still stores fault codes that correspond to specific kinds of problems, but it adds the unique ability to track problems as they
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develop and to capture a snapshot of what's going on when a problem occurs. Almost any emission problem that causes hydrocarbon emissions to exceed 1.5 times the federal limit can cause the Check Engine light to come on with OBD II - even if there is no noticeable drivability problem accompanying the emission problem.
The most powerful (and controversial) feature of OBD II is its ability to detect engine misfire. First generation OBD systems couldn't do that directly so there was no way to know if the engine was performing properly or not. OBD II misfire detection strategies vary somewhat from one vehicle manufacturer to another, but most currently use the input from the crankshaft position sensor to monitor changes in crankshaft speed. A single misfire will cause a slight variation in the rotational velocity of the crank. By knowing the position of the crank and which cylinder is supposed to be firing, the OBD II system can correlate each misfire that occurs with a specific cylinder. The misfires are tracked and tabulated, and if a pattern occurs it can set a misfire code and turn on the Check Engine light. For a detailed look at the operating parameters that can set various fault codes, Click Here to view a PDF file on GM 4.6L diagnostic parameters.
READING TROUBLE CODES A misfire that occurs in a given cylinder will set a P030X code where "X" will be the number of the cylinder that is misfiring. For example, a P0302 code would tell you cylinder number two is misfiring. But here's the important point: The code does not tell the technician why the cylinder is misfiring. He has to figure that out for himself by performing other diagnostic tests. The misfire might be due to a fouled spark plug, a bad plug wire, a defective ignition coil in a DIS system, a clogged or dead fuel injector or a loss of compression due to a leaky exhaust valve, leaky head gasket or worn cam lobe. On some vehicles, the OBD II system itself will disable a cylinder if it detects a high enough rate of misfire. This is done to protect the catalytic converter. By shutting off the cylinder's fuel injector, the OBD II system prevents unburned fuel from passing through the cylinder and entering the exhaust. Raw fuel in the exhaust is bad news because it makes the converter overheat, and if it gets too hot it can suffer damage. What else does OBD II add to the equation? It also monitors the operation of the catalytic converter with a second oxygen sensor on the tailpipe side of the converter. By comparing upstream and downstream O2 sensor readings, it can determine how well the converter is doing its job. If converter efficiency drops below a certain threshold, the OBD II system will set a code and turn on the Check Engine light. OBD II can also detect fuel vapor leaks (evaporative emissions) in the charcoal canister, evap plumbing or fuel tank by pressurizing or pulling a vacuum on the fuel system. It can even detect a loose or missing gas cap. In addition, OBD II can also generate codes for various electronic transmission problems and even air condition failures such as a compressor failure.
DIFFERENT TYPES OF FAULT CODES The diagnostic codes that are required by law on all OBD II systems are "generic" in the sense that all vehicle manufacturers
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use the same common code list and the same 16-pin diagnostic connector. Thus, a P0301 misfire code on a Ford means the same thing on a Chevy, Chrysler, Toyota or Mercedes. But each vehicle manufacturers also have the freedom to add their own "enhanced" codes to provide even more detailed information about various faults. Enhanced codes also cover nonemission related failures that occur outside the engine control system. These include ABS codes, HVAC codes, airbag codes and other body and electrical codes. The "generic" codes that are common to all vehicle manufacturers can be accessed using any basic scan tool that is OBD II compliant. An older scan tool desined for OBD I vehicles cannot read OBD II fault codes unless is has been updated with new software. Even then, many ofthese tools do not have the proper hardware for reading OBD II codes. The same applies to OBD II scan tools that are not CAN-compliant. Around 2006, most vehicles got controller area network (CAN) electrical systems that require different scan tool hardware and software to read. So make sure the scan tool you are attempting to use to read diagnostic codes is the correct one for your vehicle. Another problem you may encounter with inexpensive code readers and scan tools is that they will only read generic PO fault codes, or that they cannot read some or all of the manufacturer specific P1 fault codes. Many scan tools sold in the North American market can read Ford, GM and Chrysler P0 and P1 codes, but have little or no coverage for P1 codes on Asian and European makes.
WATCH OUT FOR FALSE CODES! Today's OBD II systems are so sensitive to misfires that they will set a misfire code if they detect as few as five misfires in 200 engine revolutions! Unfortunately, this high level of sensitivity can sometimes generate false misfire readings under certain operating conditions. Driving on an extremely rough road, for example, can produce the same kind of variations in crank speed that appear to be misfires to the OBD II monitor. Some newer OBD II systems compensate for rough road operation by reducing the level of misfire sensitivity. Others use a different method to detect misfires. Instead of monitoring crankshaft speed, the system watches the firing voltage of each spark plug to detect problems (a lean misfire typically causes a large jump in the firing voltage while a shorted or fouled plug causes a drop in the firing voltage). Random misfires that are not isolated to a particular cylinder will also set a misfire code. A P0300 code means the OBD II system has detected multiple misfires in multiple cylinders. The underlying cause in most cases is a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor. As with the individual cylinder misfire codes, the technician still has to figure out what's causing the problem and then fix it.
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Most Common Trouble Codes Copyright AA1Car What are the most common trouble codes that can cause your Check Engine light to come on and make your car or truck fail an OBD II plug-in emissions test? To find out, we asked the Illinois Environmental Protection Agency for the most common trouble codes that are causing Illinois vehicles to fail their emissions tests. Illinois requires all 1996 and newer vehicles to undergo an OBD II plug-in emissions test in the Chicago metro area, the surrounding collar counties, and in East Saint Louis. In 2009, Illinois inspected 1.67 million cars for clean air compliance. Of the vehicles tested, 6.3 percent ( a little over 100,000 vehicles) failed their initial test because of the presence of one or more trouble codes. Most Common Trouble Codes The following is the list of the 20 most common OBD II trouble codes with the percentage of failures for Illinois vehicles tested in 2009: P0420 - Catalyst System Low Efficiency - 13.2% P0171 - Fuel Trim System Lean Bank 1 - 10.4% P0401 - Exhaust Gas Recirculation (EGR) Flow Insufficient - 8.4% P0174 - Fuel Trim System Lean Bank 2 - 6.8% P0442 - Evaporative Emission (EVAP) System Small Leak Detected 6.7% P0300 - Engine Misfire Detected (random misfire) - 6.4% P0455 - Evaporative Emission (EVAP) System Leak Detected (large) 6.2% P0440 - Evaporative Emission (EVAP) System - 5.5% P0141 - Oxygen Sensor Heater (H02S) Performance Bank 1 Sensor 2 5.1% P0430 - Catalyst System Low Efficiency Bank 2 - 3.2% P0135 - Oxygen Sensor (HO2S) Performance Bank 1 Sensor 1 - 3.2% P0446 - EVAP Vent Solenoid Valve Control System - 3.1% P0128- Coolant Thermostat - 3.1% P0301 - Cylinder 1 Misfire Detected - 3.1% P0411 - EVAP System Control Incorrect Purge Flow - 2.8% P0133 - Oxygen Sensor Slow Response Bank 1 Sensor 1 - 2.8% P0303 - Cylinder 3 Misfire Detected - 2.6% P0304 - Cylinder 4 Misfire Detected - 2.6% P0302 - Cylinder 2 Misfire Detected - 2.6% P0325 - PCM Knock Sensor Circuit - 2.1%
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Based on the above data, it would seem likely that the number one most common reason for the Check Engine light coming on and failing an emissions test would be a worn out or fouled catalytic converter. But when you combine all of the related codes by system or component, you get a somewhat different picture. Looking at the data this way, these are the systems that are most likely to cause an emissions failure: Evaporative Emission System - 24.3% Engine Misfire - 17.3% Fuel Trim (lean) - 17.2% http://www.aa1car.com/library/common_trouble_codes.htm
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Catalytic converter - 16.4% Oxygen sensor related - 11.1% Exhaust Gas Recirculation (EGR) system - 8.4%
Causes of Common Trouble Codes To pass an OBD II plug-in emissions test, all of the OBD system monitors (self-tests) must have run and completed, and there must be no trouble codes found. So if your vehicle has one or more trouble codes, simply erasing the codes with a scan tool won't fix your problem. The cause of the trouble codes has to be diagnosed and repaired. The vehicle must then be driven until all of the OBD monitors complete their self-tests (which can be verified with a scan tool), and there must be no new codes. Then and only then will the vehicle pass the OBD II plug-in emissions test.
Causes of EVAP Related Codes P0411 P0440 P0442 P0446P0455 The Evaporative Emission Control system prevents fuel vapors from escaping from the fuel tank. The EVAP system includes vent hoses and a charcoal canister for capturing and storing fuel vapors, and a purge valve for siphoning the fumes into the engine when it is running. It also has a pressure or vacuum sensor for detecting small and large vapor leaks. The most common cause of a P0455 EVAP Leak Code is a loose or missing gas cap. A small leak code (P0442) may indicate a cracked or loose fuel tank vapor hose, a leaky EVAP storage canister, or a fault in the purge valve or EVAP leak detection system. You can check the gas cap yourself to make sure it fits tightly. But these other problems can be very difficult to diagnose and usually require professional help. Technicians can use a special "smoke" machine that lightly pressurizes the EVAP system and fuel tank to find leaks. The machine heats mineral oil to create a vapor-like smoke, which may also contain UV leak detection dye that makes small leaks easier to find. A professional level scan tool with bidirectional communication ability is also necessary to cycle the purge solenoid and run other EVAP self-tests. For more information about the EVAP system Click Here.
Causes of Engine Misfire Trouble Codes P0300 P0301 P0302 P0303 P0304 P0305 Misfire codes don't tell you why your engine is misfiring, only that one or more cylinders are not running properly. The OBD II system tracks misfires by detecting subtle changes in the speed of the crankshaft via the crankshaft position sensor while the engine is running. A misfire causes a slight loss of speed in the rotating crankshaft, which the OBD II system logs as a misfire. A few misfires are normal, but if the engine experiences an excessive number of misfires within a given period of time, it will set one or more misfire codes. The last digit in the code indicates the number of the cylinder that is misfiring. A P0300 code means the engine has a random misfire that jumps around from cylinder to cylinder. P0300 random misfire codes are caused by vacuum leaks (loose or cracked vacuum hoses, leaky intake manifold gaskets, or a leaky vacuum brake booster), as well as a lean fuel mixture. A lean mixture, which may also set a P0171 or P0174 code, means your engine is not getting enough fuel, or is getting too much air, possibly through a vacuum leak or a leaky EGR valve. Dirty fuel injectors or low fuel pressure can be factors that may cause a P0300 random misfire code to set. Bad gas that contains too much alcohol or water may also cause this type of code to set. Cylinder specific misfire codes (such as P0301, P0302, etc.) tell you that a specific cylinder is misfiring, but the code does not tell you why. The cause might be ignition-related (worn or fouled spark plug, bad plug wire or coil-on-plug ignition coil), fuel-related (dead or dirty fuel injector), or compression-related (bent or burned valve or leaky head gasket). All of these possibilities must be investigated to rule out the cause of the misfire. For more information about misfire diagnosis Click Here.
Causes of Fuel Trim Trouble Codes P0171 P0174 A P0171 or P0174 trouble code tells you the fuel mixture is running lean (not enough fuel and/or too much air). This type of problem can be confirmed by looking at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values with a scan tool. Normally, STFT and LTFT should be plus or minus 5 to 10 from zero. If STFT and/or LTFT are more than about +12, it indicates the engine is running lean. Negative numbers (-12 or more) indicates the engine is running rich. A lean fuel condition can be caused by: * Low fuel pressure due to a weak pump or leaky fuel pressure regulator. Use a fuel pressure gauge to check fuel pressure at idle. If fuel pressure is less than specifications, your fuel filter may be plugged, your fuel pump may be failing or have a bad wiring connection, or the fuel pressure regulator may be leaking.
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* Dirty fuel injectors. Cleaning the injectors with a fuel system additive, or having the injectors professionally cleaned may solve your problem. * Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. * Leaky EGR valve. Check the operation of EGR valve and system, and for a buildup of carbon under the valve. * Leaky PCV Valve or hose. (Check valve and hose connections) * Dirty or defective Mass Airflow Sensor (MAF). Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires.
Causes of Catalytic Converter Codes P0420 P0430 On OBD II vehicles, there is a "downstream" oxygen sensor to monitor the efficiency of the catayltic converter. If the converter has become contaminated because the engine is burning oil or leaking coolant internally, or it is worn out from age, it won't function as it should causing an increase in tailpipe emissions. The downstream oxygen sensor monitors the activity of the converter, and the engine computer compares the readings of the upstream and downstream oxygen sensors to determine how efficiently the converter is working. If efficiency drops below a certain point, it sets a P0420 or P0430 code. Nine times out of ten, either code usually means the converter has reached the end of the road and needs to be replaced. There is no way to rejuvenate a failing converter, so replacing it is your only repair option. Removing it altogether is NOT an option as this is considered to be emissions tampering. A missing converter will cause your vehicle to fail the emissions test. For more information about the catalytic converter, Click Here.
Causes of Oxygen Sensor Trouble Codes P0133 P0135 P0141 Oxygen sensors monitor the amount of oxygen in the exhaust so the engine computer (PCM) can adjust the fuel mixture to minimize emissions and maximize fuel economy. There are two types of oxygen sensor trouble codes: O2 heater circuit codes and O2 sensor codes. A heater codes will set if a fault is detected in the circuit that warms up the oxygen sensor when your engine is first started. This is necessary to reduce cold start emissions. An O2 sensor performance code will be set if the O2 sensor readings remain low (lean), or high (rich), or do not change quickly enough, or do not change at all. A low voltage (lean) oxygen sensor reading may indicate the sensor has failed, or that it is being "fooled" by an exhaust manifold vacuum leak, or a condition that allows unburned oxygen to enter the exhaust such as a burned or bend exhaust valve, or a misfiring spark plug. NOTE: If you get an oxygen sensor code plus a random misfire code and/or a MAP sensor code, the engine probably has a serious vacuum leak. For more information about oxygen sensors Click Here.
Causes of EGR Trouble Codes P0401 The Exhaust Gas Recirculation (EGR) system uses a vacuum actuated or electronic valve between the intake and exhaust manifolds to recirculates a small amount of exhaust back into the intake manifold. This occurs when the engine is at normal temperature and is accelerating or running under a heavy load. The exhaust gas dilutes the air/fuel mixture slightly to reduce combustion temperatures. This does two things; it reduces the formation of oxides or nitrogen (NOX) in the combustion chamber, and it helps the engine resist detonation (spark knock). If the EGR valve fails, or it is not flowing properly due to an accumulation of carbon under the valve, it can set an EGR trouble code. The fix is to observe and test the operation of the EGR valve and system, and to clean or remove any carbon deposits under the valve or in the intake manifold EGR passages. On Ford vehicles, EGR codes are often caused by a defective DPFE sensor in the EGR system. For more information about the EGR system, Click Here.
Causes of Coolant Thermostat Trouble Codes P0128 The thermostat speeds engine warm up after a cold start, and regulates the engine's operating temperature when it is http://www.aa1car.com/library/common_trouble_codes.htm
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running. If the thermostat sticks shut, it can cause the engine to overheat. If the thermostat fails to close, the engine may never achieve normal operating temperature. This will prevent it from going into closed loop feedback control of the fuel mixture (which makes the engine run rich and waste fuel). This code is set of conditions indicate the thermostat is not working properly. Causes of Knock Sensor Trouble Codes P0325 The knock sensor generates a signal when it detects engine vibrations that are typically produced by detonation (spark knock) during hard acceleration or when lugging the engine. The PCM uses this information to retard spark timing slightly until the detonation stops. The P0325 code may be set if the PCM gets a steady knock signal from the knock sensor. The problem may be a faulty sensor or it may be operating conditions that are causing prolonged detonation. The vibrations that may occur when driving on an unusually rough road may set a false knock sensor code. Other conditions that may contribute to spark knock include engine overheating, low octane fuel, a buildup of carbon in the combustion chambers which raises compression or loss of EGR.
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Related Articles Trouble Code Diagnostic Tips TROUBLE CODES Help Troubleshooting Ford P0171 & P0174 Lean Codes Troubleshooting a P0420 Catalyst Code Sensor Guide Making Sense of Engine Sensors Understanding Oxygen (O2) Sensors Wide Ratio Air Fuel (WRAF) Sensors Understanding Engine Management Systems Check Engine Light OnBoard Diagnostics All About Onboard Diagnostics II (OBD II) Onboard Diagnostics II Quick Reference Guide OBD II Diagnostic Tips Zeroing in on OBD II Diagnostics OBD Monitor Not Ready Advanced Diagnostics: Mode 06 Scan Tool Diagnostics Scan Tool Companion Driveability Diagnosis: Misfires Exhaust Gas Recirculation (EGR) EVAP Evaporative Emission Control System
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Diagnostic Trouble Code Help Copyright AA1Car
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. A Diagnostic Trouble Code (DTC) is set in a vehicle's onboard computer when a fault occurs in any monitored system. The code number corresponds to the type of fault, and can be used to diagnose the problem. When an engine is running and the computer detects a problem in one of its sensor or output circuits, or even within itself, it will set a trouble code. In some systems, the trouble code number is retained in memory. In others, the trouble code is not stored but is regenerated when a mechanic runs the system through a special self-diagnostic test. A trouble code will turn on the Check Engine Light (malfunction indicator lamp or MIL) to alert the driver the vehicle has a problem. To diagnose the fault, a code reader or scan tool is connected to the vehicle diagnostic connector to read the trouble code. Some tools display a definition for the code, while others show only a trouble code number. You then have to look up the definition of the trouble code number in a manual or a database to find out what it means. Listed below are links to "generic" OBD II codes and their definitions (codes that are common to all makes and models of vehicles). Vehicle manufacturers also use additional codes that are not in the generic code lists. These are called "enhanced" or OEM-specific codes. On many older (pre-1995) vehicles, a trouble code can be read without a scan tool or code reader using a manual flash code procedure. Once a trouble code has been found, the next step is to diagnose the fault. NOTE: A trouble code by itself does NOT tell you which part to replace. You must diagnose the system, sensor and/or circuit to determine the fault before repairs are made or any parts are replaced. Once you have a trouble code, the next step is figuring out why it set. Many codes are for systems, circuits or operating situations rather than individual sensors or other components, so additional tests are usually necessary to isolate and identify the fault that caused the trouble code to set. Scan Tool Companion is a computer reference program that can help you diagnose these kind of faults. It includes takes the information on this page to the next level and provides guidance on which PIDs to look at on a scan tool when diagnosing a code, what to check when you have a specific code, and often provides "good" values to look for. Scan Tool Companion also provides diagnostic guidance by vehicle symptom and by system.
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HOW TO USE TROUBLE CODES The following tips don't cover all possibilities, but they may help you identify a problem more quickly:
OXYGEN SENSOR TROUBLE CODES There are two types of Oxygen Sensor trouble codes: O2 heater circuit codes and O2 sensor codes. O2 Heater circuit related codes include P0036, P0037, P0038, P0042, P0043, P0044, P0050, P0051, P0052, P0056, P0057, P0058, P0062, P0063, P0064 & P0141. O2 Sensor related codes include P0130 through P0140, P0142 through P0147, P0150 through P0167 The heater codes will set if a fault is detected in the O2 sensor heater circuit. The O2 sensor codes will be set if the O2 sensor readings remain low (lean), or high (rich), or do not change quickly enough, or do not change at all. The O2 sensor reads unburned oxygen in the exhaust, and generates a voltage signal that is proportional to the amount of oxygen in the exhaust. The signal can vary from a low of about 0.1 volts up to a high of about 0.9 volts. A low voltage signal indicates a lean fuel mixture. A high voltage signal indicates a rich fuel mixture. The engine computer uses the O2 sensor's input to balance the fuel mixture during closed loop operation. A bad sensor may prevent the system from going into closed loop, and usually causes the fuel mixture to run rich causing an increase in fuel consumption and emissions. A low voltage (lean) reading may indicate a bad O2 sensor, a vacuum leak, or a condition that allows unburned oxygen to enter the exhaust. Check intake vacuum at idle, and inspect vacuum hose connections. If okay, check for a misfiring cylinder, a burned exhaust valve that is leaking compression, or a leaky exhaust manifold gasket. O2 sensor quick checks include watching the sensor's output voltage as the fuel mixture changes. Momentarily disconnecting a vacuum hose will cause a lean response from the O2 sensor. No change in the reading or a very sluggish response would indicate a bad O2 sensor. NOTE: If you get an oxygen sensor code plus a random misfire code and a MAP sensor code, the engine probably has a serious vacuum leak.
LEAN TROUBLE CODES (P0171 or P0174) A code P0171 or P0174 indicate the engine is running lean. This means there is too much air and/or not enough fuel. You can confirm the engine is running lean by looking at Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Normally, STFT and LTFT should be plus or minus 5 to 10 from zero. If STFT and/or LTFT are more than about +12, it indicates the engine is running lean. Negative numbers (-12 or more) indicates the engine is running rich. A lean fuel condition can be caused by: * Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (use a fuel pressure gauge to check fuel pressure at idle) * Dirty fuel injectors. (try cleaning the injectors) * Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum) * Leaky EGR valve. (Check operation of EGR valve) * Leaky PCV Valve or hose. (Check valve and hose connections) * Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)
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RICH TROUBLE CODES Rich codes include P0172 & P0175. Typical symptoms of an engine that is running rich (too much fuel, not enough air) are poor fuel economy, elevated emissions (Carbon monoxide or CO), and engine may have rough idle or surge condition. Possible causes include a bad O2 sensor, excessive fuel pressure (bad fuel pressure regulator or plugged return line), leaky fuel injectors, dirty air filter or restricted air inlet, or a defective coolant sensor that prevents the engine management system from going into closed loop mode.
Bosch and NTK O2 Sensors OE Style Direct Fit O2 Sensors Wideband Oxygen Sensors MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR TROUBLE CODES These include P0105, P0106, P0107, P0108 & P0109, and can be set if the MAP sensor output remains too high or too low (out of range), or the MAP sensor readings do not correspond to the Throttle Position Sensor (TPS) readings. MAP sensors monitor changes in intake vacuum, which is a way of determining engine load. When engine load goes up, intake vacuum drops. Vacuum is highest at idle and drops during acceleration and wide open throttle. The computer uses the MAP sensor's input to vary ignition timing and the fuel mixture. So a MAP sensor problem may cause drivability problems such as surging, poor fuel economy and performance. MAP sensors either generate a voltage or frequency signal as engine vacuum (load) changes. Vacuum leaks can cause problems with the sensor's reading, so check for leaks and the sensor's vacuum connection to the engine. How to check: a MAP sensor's voltage or frequency output should change when engine vacuum (load) changes. If you don't see a change, the sensor is probably bad and should be replaced.
THROTTLE POSITION TROUBLE SENSOR (TPS) CODES These include P0120 through P0229, and can be set if the TPS readings are too high or too low (out of range), if the signal is lost, or if the signal does not correspond to the MAP sensor's readings. The TPS sensor monitors the position of the throttle so the computer can add more fuel when the engine is accelerating or under load. The computer may also need to know when the throttle is at idle or wide open to control other functions. A bad TPS can cause driveability problems such as hesitation. The sensor's resistance changes as the throttle moves, causing the return voltage signal to vary. Look for a change in the voltage output as the throttle opens and closes. No change or skips in the output would indicate a faulty TPS sensor. Also note: the idle voltage is adjustable on some TPS sensors and must be set within specifications for accurate operation. If the voltage adjustment is not within specifications, it can adversely affect performance and throttle response.
COOLANT SENSOR TROUBLE CODES Coolant sensor codes include P0115 through P0119, and can be set if the coolant sensor readings do not change as the engine warms up, if the readings are too high or too low (out of range), if there is no signal from the sensor, or if the engine overheats. The coolant sensor monitors engine temperature. This is a key function because it allows the fuel management system to go into the closed loop mode of operation when the engine warms up. The computer also uses engine temperature to control other functions, too. A failure here can prevent the system from going into closed loop causing a rich fuel mixture, and an increase in fuel consumption and emissions. A coolant sensor's resistance changes as the temperature increases. If you do not see a change in the resistance as the engine warms up, or the resistance is out of specifications, the sensor is bad. Other things that can cause bad sensor readings include a low coolant level in the cooling system, a thermostat that is stuck http://www.aa1car.com/library/trouble_code.htm
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open or shut, or a thermostat that has the wrong temperature rating for the engine. CAUTION: Do not open the radiator cap if the coolant is hot! Wait until the engine and radiator have cooled to open the cap.
MISFIRE TROUBLE CODES This includes P0300 and P0301 through P0312. The P0300 code is a random misfire code while all the other misfire codes denote a misfire problem in a specific cylinder. The last digit in the code tells which cylinder is misfiring. Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel. A Random Misfire code often indicates a vacuum leak or bad gas. If a misfire in a specific cylinder should lead you to check the spark plug, fuel injector and compression.
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Related Articles & Resources: Most Common Trouble Codes (and what causes them) Troubleshooting Ford P0171 & P0174 Lean Codes Troubleshooting a P0420 Catalyst Code Sensor Guide Making Sense of Engine Sensors Coolant Sensors Crankshaft Position CKP Sensors Understanding Oxygen (O2) Sensors Wide Ratio Air Fuel (WRAF) Sensors Sensing Emission Problems (O2 Sensors) MAP sensors Mass Airflow MAF Sensors Vane Airflow VAF Sensors Throttle Position Sensors Understanding Engine Management Systems Powertrain control modules (PCMs) Flash Reprogramming PCMs Check Engine Light OnBoard Diagnostics All About Onboard Diagnostics II (OBD II) Onboard Diagnostics II Quick Reference Guide OBD II Diagnostic Tips Zeroing in on OBD II Diagnostics OBD Monitor Not Ready Advanced Diagnostics: Mode 06 Controller Area Network (CAN) Diagnostics Choosing a Scan Tool Scan Tool Diagnostics Scan Tool Companion Diagnostic Tools & Equipment Driveability Diagnosis: Misfires
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Understanding Onboard Diagnostics OBDII: Past, Present & Future Copyright AA1Car Adapted from an article written by Larry Carley for Underhood Service magazine
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. Though the technology is still relatively new and has not had a big impact on the aftermarket yet, it will. The technology we are referring to is OBDII, the government mandated onboard diagnostic system for tattling on emission failures. All 1996 and newer model year passenger cars and light trucks are OBDII-equipped, but the first applications were actually introduced back in 1994 on a limited number of vehicle models (see box). What makes OBDII different from all the self-diagnostic systems that proceeded it is that OBDII is strictly emissions oriented. In other words, it will illuminate the Malfunction Indicator Lamp (MIL) anytime a vehicle's hydrocarbon (HC), carbon monoxide (CO), oxides of nitrogen (NOX) or evaporative emissions exceed 1.5 times the federal test procedure (FTP) standards for that model year of vehicle. That includes anytime random misfires cause an overall rise in HC emissions, anytime the operating efficiency of the catalytic converter drops below a certain threshold, anytime the system detects air leakage in the sealed fuel system, anytime a fault in the EGR system causes NOX emissions to go up, or anytime a key sensor or other emission control device fails. In other words, the MIL light may come on even though the vehicle seems to be running normally and there are no real driveability problems. The main purpose of the MIL lamp on an OBDII-equipped vehicle, therefore, is to alert motorists when their vehicles are polluting so they will get their emission problems fixed. But as we all know, motorist are very good at ignoring warning lamps, even when steam is belching from under the hood or the engine is making horrible noises. That is why regulators want to incorporate OBDII into existing and enhanced vehicle emissions inspection programs. If the MIL lamp is found to be on when a vehicle is tested, it does not pass even if its tailpipe emissions are within acceptable limits.
WHY OBDII? The problem with most vehicle inspection programs is that they were developed back in the 1980s to identify "gross polluters." The tests were designed primarily to measure idle emissions on carbureted engines (which are dirtiest at idle), and to check for only two pollutants: unburned hydrocarbons (HC) and carbon monoxide (CO). The pass/fail cut points that were established for the various model years were also made rather lenient to minimize the number of failures. Consequently, a lot of late model vehicles that should not be passing an emissions test are getting through anyway. Efforts to upgrade vehicle inspection programs to the new I/M 240 standards stalled because of a lack of public and political support. I/M 240 requires "loaded-mode" emissions testing on a dyno while the vehicle is driven at various speeds following a carefully prescribed driving trace. The tailpipe gases are then analyzed to check not only total HC and CO emissions (in http://www.aa1car.com/library/us796obd.htm
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grams rather than parts per million or percent), but also oxides of nitrogen (NOX). The total emissions for the entire 240second driving cycle is averaged for a composite emission score that determines whether or not the vehicle passes the test. Also included is an evaporative purge flow test to measure the flow rate of the canister purge valve, and an engine off pressure test of the evaporative emission control system to check the fuel tank, lines and cap for leaks. The I/M 240 program was to have been required in most areas of the country that do not meet national ambient air quality (NAAQ) standards. But after the program faltered in Maine, many states balked and only some went ahead with the I/M 240 program. The cost and complexity of the I/M 240 program combined with less than enthusiastic public acceptance doomed it from the start. So most states are now using a simple OBD II plug-in test to check emissions compliance on 1996 and newer cars and trucks.
A SHORT HISTORY WITH FAR REACHING IMPLICATIONS
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The origins of OBDII actually date back to 1982 in California, when the California Air Resources Board (ARB) began developing regulations that would require all vehicles sold in that state starting in 1988 to have an onboard diagnostic system to detect emission failures. The original onboard diagnostic system (which has since become known as OBDI) was relatively simple and only monitored the oxygen sensor, EGR system, fuel delivery system and engine control module. OBDI was a step in the right direction, but lacked any requirement for standardization between different makes and models of vehicles. You still had to have different adapters to work on different vehicles, and some systems could only be accessed with costly "dealer" scan tools. So when ARB set about to develop standards for the current OBDII system, standardization was a priority: a standardized 16-pin data link connector (DLC) with specific pins assigned specific functions, standardized electronic protocols, standardized diagnostic trouble codes (DTCs), and standardized terminology. Another limitation of OBDI was that it could not detect certain kinds of problems such as a dead catalytic converter or one that had been removed. Nor could it detect ignition misfires or evaporative emission problems. Furthermore, OBDI systems would only illuminate the MIL light after a failure had occurred. It had no way of monitoring progressive deterioration of emissions-related components. So it became apparent that a more sophisticated system would be required. The California Air Resources Board eventually developed standards for the next generation OBD system, which were proposed in 1989 and became known as OBDII. The new standards required a phase-in starting in 1994. The auto makers were given until the 1996 model year to complete the phase-in for their California vehicles.
Similar standards were incorporated into the federal Clean Air Act in 1990 which also required all 49-state vehicles to be OBDII equipped by 1996 -- with one loophole. The OBDII systems would not have to be fully compliant until 1999. So some 1996 OBDII systems may lack one of the features normally required to meet the OBDII specs, such as the evaporative emissions purge test.
EARLY OBDII APPLICATIONS 1994 vehicles equipped with the early OBD II systems include Buick Regal 3800 V6, Corvette, Lexus ES3000, Toyota Camry (1MZ-FE 3.0L V6) and T100 pickup (3RZ-FE 2.7L four), Ford Thunderbird & Cougar 4.6L V8, and Mustang 3.8L V6. 1995 vehicles with OBDII include Chevy/GMC S, T-Series pickups, Blazer and Jimmy 4.3L V6, Ford Contour & Mercury Mystique 2.0L four & 2.6L V6, Chrysler Neon, Cirrus and Dodge Stratus, Eagle Talon 2.0L DOHC (nonturbo), and Nissan Maxima and 240 SX. Not all of these early applications are fully OBDII compliant, but do include the major diagnostic features of the current system.
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OBDII HARDWARE UPGRADES Don't think for a moment that OBDII is just a fancier version of self-diagnostic software. It is that and much, much more. OBDII-equipped vehicles typically have: Twice the number of oxygen sensors as non-OBDII vehicles (most of which are heated O2 sensors). The additional O2 sensors are located downstream of the catalytic converter. More powerful powertrain control modules, with either 16-bit (Chrysler) or 32-bit (Ford & GM) processors to handle up to 15,000 new calibration constants that were added by OBDII. Electronically Erasable Programmable Read Only Memory (EEPROM) chips that allows the PCM to be reprogrammed with revised or updated software changes using a terminal link or external computer. A modified evaporative emission control systems with a diagnostic switch for purge testing, or an enhanced EVAP system with a vent solenoid, fuel tank pressure sensor and diagnostic test fitting, More EGR systems with a linear EGR valve that is electronically operated and has a pintle position sensor. Sequential fuel injection rather than multiport or throttle body injection. Both a MAP sensor and MAF sensor for monitoring engine load and airflow.
TOOLING UP FOR OBDII To work on an OBDII-equipped vehicle, you must have an OBD II compliant scan tool. Many scan tools made prior to 1996 are not OBD II compatible and cannot be upgraded with a simple cartridge change. You need a hardware adapter for these older scan tools or a newer scan tool that is OBD II compatible. Dealer technicians don't have it any better. GM requires a Tech 2 scan tool for its 1996 and newer vehicles. The Tech 2 scan tool has a 9 parameter screen display, a 5 parameter freeze option for scrolling, bar graph and line chart capabilities, current data capture and the ability to store two snapshots (of data, not your wife and kids). Likewise, Chrysler has its DRB III tool, and Ford has its New generation Star tester for OBDII-equipped vehicles from 1994 and up. If you are looking for a good reference book on OBDII, GM has an excellent training manual "On-Board Diagnostics Generation Two" P/N 16030.02-1. The book costs $20 and is available through Mascotech Marketing Services, 1972 Brown Road, Auburn Hills, MI 48326 (1-800-393-4831). THAT PESKY MIL LAMP Most technicians are pretty familiar with the operation of the "Check Engine" or "Malfunction Indicator Lamp" (MIL) on late model vehicles. But on OBDII-equipped vehicles, it may seem like the MIL lamp has a mind of its own. On 1996 General Motors J-, N- and H-body cars, several rental fleets have encountered problems with the MIL lamp coming on because motorists and fleet personnel have not been using the correct refueling procedure when filling the fuel tank with gas. On these cars, the OBDII system applies vacuum to the evaporative emissions control system to check for air leakage. If the gas cap is not tight or the tank is filled while the key is on or the engine is idling, it can trigger a false P0440 code causing the MIL light to come on. GM is advising its dealers and fleet customers to reflash the EEPROM with revised OBDII programming that waits to check the evaporative emissions system until the vehicle is in motion. Bad gas has also been causing some false MIL lights. When the vehicle is diagnosed, the technician finds a P0300 random misfire code which would normally be set by a lean misfire condition due to a vacuum leak, low fuel pressure, dirty injectors, etc., or an ignition problem such as fouled plugs, bad plug wires, weak coil, etc. The OBDII self-diagnostics tracks misfires by individual cylinder, and considers up to a 2% misfire rate as normal. But water in the gas or variations in the additive package in reformulated gasoline in some areas of the country can increase the misfire rate to the point where it triggers a code. To minimize the occurrence of false MIL lamps, the OBDII system is programmed so that the MIL lamp only comes on if a certain kind of fault has been detected twice under the same driving conditions. With other faults (those that typically cause http://www.aa1car.com/library/us796obd.htm
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an immediate and significant jump in emissions), the MIL light comes on after only a single occurrence. So to correctly diagnose a problem, it is important to know what type of code you are dealing with. Type A diagnostic trouble codes are the most serious and will trigger the MIL lamp with only one occurrence. When a Type A code is set, the OBDII system also stores a history code, failure record and freeze frame data to help you diagnose the problem. Type B codes are less serious emission problems and must occur at least once on two consecutive trips before the MIL lamp will come on. If a fault occurs on one trip but does not happen again on the next trip, the code won't "mature" and the light will remain off. When the conditions are met to turn on the MIL lamp, a history code, failure record and freeze frame data are stored the same as with Type A codes. A drive cycle or trip, by the way, is not just an ignition cycle, but a warm-up cycle. It is defined as starting the engine and driving the vehicle long enough to raise the coolant temperature at least 40 degrees F (if the startup temperature is less than 160 degrees F). Once a Type A or B code has been set, the MIL will come on and remain on until the component that failed passes a selftest on three consecutive trips. And if the fault involved something like a P0300 random misfire or a fuel balance problem, the light will not go out until the system passes a self-test under similar operating conditions (within 375 rpm and 10% of load) that originally caused it to fail. That is why the MIL lamp will not go out until the emissions problem has been repaired. Clearing the codes with a scan tool or disconnecting the powertrain control module power supply will not prevent the lamp from coming back on if the problem has not been fixed. It may take one or more driving cycles to reset the code, but sooner or later the MIL lamp will go back on if the problem is still there. Likewise, the MIL won't necessarily go on if you intentionally disconnect a sensor. It depends on the priority ranking of the sensor (how it affects emissions), and how many driving cycles it takes for the OBDII diagnostics to pick up the fault and set a code. As for Type C and D codes, these are non-emissions related. Type C codes can cause the MIL lamp to come on (or illuminate another warning lamp), but Type D codes do not cause the MIL lamp to come on.
RUNNING AN OBDII DRIVE CYCLE Suppose you have "fixed" an emissions problem on an OBDII-equipped vehicle. How can you check your work? By performing what is called an "OBDII drive cycle." The purpose of the OBDII drive cycle is to run all of the onboard diagnostics. The drive cycle should be performed after you have erased any trouble codes from the PCM memory, or after the battery has been disconnected. Running through the drive cycle sets all the system monitors so that subsequent faults can be detected. The OBDII drive cycle begins with a cold start (coolant temperature below 122 degrees F and the coolant and air temperature sensors within 11 degrees of one another). NOTE: The ignition key must not be on prior to the cold start otherwise the heated oxygen sensor diagnostic may not run. 1. As soon as the engine starts, idle the engine in drive for two and a half minutes with the A/C and rear defrost on. OBDII checks oxygen sensor heater circuits, air pump and EVAP purge. 2. Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle. OBDII checks for ignition misfire, fuel trim and canister purge. 3. Hold at a steady state speed of 55 mph for three minutes. OBDII monitors EGR, air pump, O2 sensors and canister purge. 4. Decelerate (coast down) to 20 mph without braking or depressing the clutch. OBDII checks EGR and purge functions. 5. Accelerate back to 55 to 60 mph at half throttle. OBDII checks misfire, fuel trim and purge again. 6. Hold at a steady speed of 55 to 60 mph for five minutes. OBDII monitors catalytic converter efficiency, misfire, EGR, fuel trim, oxygen sensors and purge functions.
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7. Decelerate (coast down) to a stop without braking. OBDII makes a final check of EGR and canister purge.
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BEYOND OBDII OBDII is a very sophisticated and capable system for detecting emissions problems. But when it comes to getting motorists to fix emission problems, it is no more effective than OBDI. Unless there is some type of mandatory enforcement, such as checking the MIL light during an emissions inspection, OBDII is just another idiot light. Currently under development are plans for OBDIII, which would take OBDII a step further by adding telemetry. Using miniature radio transponder technology similar to that which is already being used for automatic electronic toll collection systems, an OBDIII-equipped vehicle would be able to report emissions problems directly to a regulatory agency. The transponder would communicate the vehicle VIN number and any diagnostic codes that were present. The system could be set up to automatically report an emissions problem via a cellular or satellite link the instant the MIL light comes on, or to answer a query from a cellular, satellite or roadside signal as to its current emissions performance status. What makes this approach so attractive to regulators is its effectiveness and cost savings. Under the current system, the entire vehicle fleet in an area or state has to be inspected once every year or two to identify the 30% or so vehicles that have emissions problems. With remote monitoring via the onboard telemetry on an OBDIII-equipped vehicle, the need for periodic inspections could be eliminated because only those vehicles that reported problems would have to be tested. In effect, GM is essentially offering that now with their OnStar system on 2004, 2005 and 2006 vehicles. OnStar monitors the OBD II system and notifies the driver if a fault is detected. GM says by detecting problems early, it can reduce repair costs (and save GM a bundle in warranty costs). On one hand, OBDIII with its telemetry reporting of emission problems would save consumers the inconvenience and cost of having to subject their vehicle to an annual or biennial emissions test. As long as their vehicle reported no emission problems, there would be no need to test it. On the other hand, should an emissions problem be detected, it would be much harder to avoid having it fixed, which is the goal of all clean air programs anyway. By zeroing in on the vehicles that are actually causing the most pollution, significant gains could be made in improving our nation's air quality. But as it is now, polluters may escape detection and repair for up to two years in areas that have biennial inspections. And in areas that have no inspection programs, there is no way to identify such vehicles. OBDIII would change all that. According to Mark Carlock with California's Air Resources Board, the technology exists now to make OBDIII possible. "The idea is to streamline the inspection process by only inspecting those vehicles that really need it." Carlock says the technology to do so is "no big deal." But he concedes that it might be years before OBDIII is actually be required on new vehicles. A prototype system built by GM Hughes Electronics has already been evaluated by ARB that uses a roadside transmitter to interrogate vehicles as they pass by. The system uses ultra low power 10 milliwatt receiver stations and 1 milliwatt transmitters (which is about 1,000 times less power than a typical cellular telephone) with a broadcast frequency of 915 Mhz. The system is reportedly capable of retrieving information from 8 lanes of bumper-to-bumper traffic whizzing by at speeds up to 100 mph! When the vehicle receiver hears the query signal from a stationary or portable roadside transmitter, it transmits back an answer in the form of the vehicle's 17-digit VIN number plus an "okay" signal or any trouble codes that may be present. The information can then be used to identify vehicles that are in violation of clean air statutes so a notice can be sent that repairs and/or smog testing is required. Or, the information could be used on the spot to identify vehicles for a pullover roadside emissions check or issuing an emissions citation. The projected cost of such a system would be $50 per vehicle, says Carlock, based on similar transponders that are in use for electronic toll collecting. The transponders are about the size of a small calculator.
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The same basic approach could also be used with existing cellular phone links (local station networks) and/or satellite systems. To keep motorists from tampering with or disabling their telemetry systems, vehicles could be interrogated randomly or on a scheduled basis to monitor their condition. The OBDIII telemetry could also be combined with global positioning system (GPS) technology to document or monitor the whereabouts of vehicles. Orbiting 11,000 miles above the earth's surface are 24 military satellites that make up the Navstar global positioning system. By timing radio signals from these satellites, the position of a vehicle, boat or plane anywhere on the earth can be fixed within a few meters. The GPS system is currently used by many fleets for tracking the whereabouts of their vehicles as well as by onboard navigation systems for pinpointing a vehicle's location on an electronic map. The advantages of using a satellite based telemetry system for OBDIII rather than a roadside system are: Greater coverage of the entire vehicle population for more accurate surveillance. Vehicles could be monitored and queried no matter where they were, even while sitting in a garage or driveway. There would be no way to avoid the watchful eye of the emissions police. Being able to locate vehicles that are in violation of clean air statutes, either for "demographic studies" or to track down and arrest violators. Being able to monitor the whereabouts of vehicles for purposes other than emissions surveillance such as recovering stolen vehicles (like the LoJack anti-theft system ), keeping tabs on suspected drug dealers, gang members and other undesirables. Being able to disable vehicles that belong to emission scofflaws by transmitting a secret code. Law enforcement officers might also be able to use such a code to disable a vehicle fleeing from a crime scene or one that belonged to someone with a backlog of unpaid traffic violations. The specter of having Big Brother in every engine compartment and driving a vehicle that rats on itself anytime it pollutes is not one that would appeal to many motorists. So the merits of OBDIII would have to be sold to the public based on its cost savings, convenience and ability to make a real difference in air quality. Even so, any serious attempt to require OBDIII may run afoul of Fourth Amendment issues over rights of privacy and protection from government search and seizure. Does the government have the right to snoop under your hood anytime it chooses to do so, or to monitor the whereabouts of your vehicle? These issues will have to be debated and resolved before OBDIII stands a chance of being accepted. Another change that might come with OBDIII would be even closer scrutiny of vehicle emissions. The misfire detection algorithms currently required by OBDII only watch for misfires during driving conditions that occur during the federal driving cycle, which covers idle to 55 mph and moderate acceleration. It does not monitor misfires during wide open throttle acceleration. Full range misfire detection has been required since 1997. OBDIII could go even further by requiring "fly-by-wire" throttle controls to reduce the possibility of misfires on the coming generation of low emission and ultra low emission vehicles.
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Related Articles: Trouble Code Diagnostic Tips Most Common Trouble Codes (and what causes them) Making Sense of Engine Sensors Oxygen Sensor Locations Understanding Engine Management Systems Powertrain control modules (PCMs) Flash Reprogramming PCMs Zeroing in on OBD II Diagnostics OBD II Diagnostic Tips OBD Monitor Not Ready OBD II Emissions Testing Controller Area Network (CAN) Diagnostics http://www.aa1car.com/library/us796obd.htm
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OBD Monitor Not Ready Copyright AA1Car You've driven your vehicle to the emissions test station to have it tested, but your vehicle was rejected because it was "Not Ready." What exactly does "Not Ready" mean? It means your Onboard Diagnostic System (OBD II) has NOT completed all of its self-test monitors that keep an eye on the performance of your emissions control systems. Depending on the year, make and model of your vehicle, there may be half a dozen or more OBD monitors that must have completed. A single or multiple "NOT READY" indications will prevent your vehicle from passing the emissions inspection. To pass an OBD II plug-in emissions inspection test, all of the OBD monitors must have run and successfully completed with http://www.aa1car.com/library/obd_monitor_not_ready.htm
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no faults found. This tells the emissions test computer that your vehicle is performing within emissions limits for your year, make and model, and that your vehicle is in compliance with the applicable emissions laws, and that your vehicle is not polluting. The OBD system monitors some functions every time you drive your vehicle, but only checks other functions under certain driving or operating conditions. Some checks are "continuous" and are ongoing all the time. The continuous checks include: Misfire Monitoring to detect ignition and fuel related misfires that may cause emissions to increase and/or damage to the catalytic converter. Fuel System Monitoring to detect changes in fuel mixture that may cause emissions to increase. Comprehensive Component Monitoring to detect any major faults in engine sensors that may cause emissions to increase. The OBD monitors that only run under certain conditions include the EVAP monitor, HEGO monitor (Heated Exhaust Gas Oxygen sensor), and the Catalyst Efficiency monitor.
Three OBD monitors on this vehicle are NOT READY: the Catalyst, EVAP and HEGO oxygen sensor monitors.
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EVAP Monitor Not Ready The EVAP (Evaporative Emission Control System) monitor checks for fuel vapor leaks (including a loose or missing gas cap). As a rule, the EVAP monitor only runs when certain conditions have been met. If these conditions have not been met since the last time the monitor ran, or since the last time the battery was disconnected, or since the last time fault codes were cleared from the PCM memory, the EVAP monitor will NOT be ready. The requirements for running the EVAP monitor vary depending on the year, make and model of your vehicle. Generally speaking, the fuel tank must be 1/4 to 3/4 full because a near empty tank or a full tank can affect the accuracy of the EVAP
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self-test. The ambient outside temperature must not be too hot (above 95 degrees) to too cold (below 30 degrees) because this affects fuel volatility and the amount of vapor inside the tank. The vehicle must also have sit overnight or for 8 hours or more without being driven. On some vehicles, the EVAP monitor runs when the vehicle has been cruising on the highway at light throttle at a speed of 45 to 65 mph for at least 10 minutes or more. All of the components in the EVAP control system must also be functioning normally. The presence of any EVAP-related fault codes will prevent the EVAP monitor from running. The EVAP monitor checks for vapor leaks by applying vacuum or pressure to the fuel tank, vapor lines and charcoal canister. If it detects no airflow when the EVAP canister purge valve is opened, or it detects a leak that equals or exceeds the amount of air that would pass through a hole 0.040 inches in diameter (0.020 inches for 2000 and up model year vehicles), it logs a trouble code in the P0440 to P0457 range.
EVAP Drive Cycles The following are sample drive cycles for the EVAP monitor: Ford: With fuel tank one half to three-quarters full, cruise at 45 to 65 mph for 10 minutes. Avoid sharp turns and hills during this period. Chrysler: There are two-parts to this test. The first part runs after idling for five minutes, then driving at 30 to 45 mph for two minutes (fuel tank must be half to 85 percent full). The second part runs after the vehicle has sit for 8 or more hours (cold soak) without being driven. Start the engine and idle for four minutes, then drive in stop-and-go traffic for five minutes using smooth accelerations and decelerations. Stop and idle for 4 minutes. The EVAP monitor should be complete.
HEGO Monitor Not Ready The Heated Exhaust Gas Oxygen sensor monitor makes sure the oxygen sensors are functioning properly and are operating within their normal range. The monitor runs after the engine has reached normal operating temperature, and the vehicle is cruising at a specified speed for a specified length of time. This monitor will not run if there are any faults in the oxygen sensor heater circuit, if there are any pending oxygen sensor codes, or the engine coolant or vehicle speed sensors are not functioning normally. If the HEGO monitor is NOT ready, it will prevent the catalyst efficiency monitor from running, causing yet another Not Ready to be tallied against you!
HEGO Drive Cycles The following are some sample drive cycle requirements for the HEGO monitor to run: Ford: The HEGO monitor should run when the engine has reached normal operating temperature, the inlet air temperature is between 40 and 100 degrees F, and the vehicle is cruising at a steady 40 mph for four minutes. GM: GM uses a two-part HEGO monitor. The first part of the HEGO monitor runs after idling the engine for two and a half minutes with the A/C and rear defroster on. This checks the O2 heater circuit. After this, turn the A/C and defroster off, then accelerate at halt throttle to 5 mph and hold at a steady 55 mph for three minutes. This will complete the second half of the HEGO monitor that checks the responsiveness of the O2 sensors. Chrysler: Idle for five minutes (to reach closed loop operation). Then drive at a steady vehicle speed above 25 mph for two minutes. Stop and idle for 30 seconds. Then smoothly accelerate to 30 to 40 mph. Repeat the last two steps five times. Toyota: The HEGO monitor should run after idling the engine for nine minutes, then driving at a steady 25 mph for two minutes.
Catalyst Efficiency Monitor Not Ready The Catalyst Efficiency Monitor verifies the catalytic converter is operating at high enough efficiency to keep exhaust emissions within acceptable limits. The monitor compares the signals from the upstream and downstream oxygen sensors to monitor the operation of the catalytic converter. If catalyst efficiency has dropped below a certain threshold, this monitor will set a converter fault code (P0420 and/or P0-439) and turn on the Check Engine light. As a rule, if converter conversion efficiency drops below 80 percent for any pollutant (carbon monoxide, hydrocarbons or http://www.aa1car.com/library/obd_monitor_not_ready.htm
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oxides of nitrogen), the vehicle may be polluting, causing a code to set. On late model Low Emission Vehicles (LEV) and Ultra Low Emission Vehicles (ULEV), there's even less margin for error. The catalyst monitor may set a code if converter efficiency is less than 90 percent. The catalyst monitor may also requires specific driving conditions before it will run. Depending on the vehicle application, this usually includes completing the HEGO (oxygen sensor) monitors first, followed by driving at highway speeds (60 to 65 mph) for at least 10 to 15 minutes under light load, no conflicts with other monitors that have not yet run (such as EVAP or EGR monitors which may have to complete before the catalyst monitor will run), and no fault codes that could affect the accuracy of the test. Some vehicles have very specific drive cycles that must be followed before the catalyst monitor will run. In some cases, it may even be necessary to complete the prescribed drive cycle several times before the catalyst monitor will run.
Catalyst Monitor Drive Cycles The following are some sample drive cycles for the catalyst monitor to run: Ford: The catalyst monitor will not run until the HEGO (oxygen sensor) monitor has run and completed successfully with no faults found. The vehicle must then be driven in stop-and-go traffic conditions at five different cruise speeds ranging from 25 to 45 mph over a period of 10 minutes. GM: The catalyst monitor runs after cruising at 55 mph for 5 minutes, but it make take up to five drive cycles at this speed before the monitor will run! Chrysler: The catalyst monitor will NOT run unless the Check Engine light is off, no fault codes are present, the fuel level is between 15 and 85 percent full, and the coolant temperature is above 70 degrees F. If these conditions have been met, the engine must have run at least 90 seconds, and the engine speed must be between 1,350 and 1,900 rpm. Idle vehicle for five minutes (to reach closed loop operation), the drive at a steady speed between 30 and 45 mph for two minutes. Toyota: The catalyst monitor will run after driving the vehicle at 40 to 55 mph for seven minutes, followed by driving at 35 to 45 mph for another seven minutes.
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Just because a scan tool check shows no codes found doesn't mean your vehicle will pass emissions. All of the OBD monitors must also be complete for your vehicle to be test ready. On this Innova scan tool, the emissions ready status is shown with colored LED lights. GREEN means no faults and the vehicle is ready to pass. YELLOW means one or more OBD monitors have not completed and the vehicle is NOT ready for testing. RED means one or more fault codes. Repairs are needed before the vehicle will pass.
Common Causes of Not Ready Rejection for Emissions Testing All of the applicable OBD monitors for your year, make and model of vehicle must have run and completed to be accepted and pass an OBD plug-in emission test. Any of the following may cause your vehicle to not be ready: Disconnecting the battery for any reason. This erases the memory in the PCM, including stored fault codes and previous OBD monitor test results. It's like resetting the clock back to zero. Consequently, it may take several days (or even weeks) of driving before all of the monitors will run, allowing your vehicle to be tested. Erasing stored codes with a scan tool. This also resets all of the monitors back to zero, so allow plenty of time for the monitors to run before driving back to the emissions test facility. If any of the erased fault codes reappear, it may prevent one or more of the monitors from completing. Disconnecting sensors. This will prevent the monitors from running and will likely set one or more fault codes. Removing the catalyst converter. This is emissions tampering and is illegal for street-driven vehicles. Installing a Performance Tune with an Aftermarket Tuner Tool. This changes the stock programming and calibration of the engine computer. Such changes are often made to increase power, change shift points, recalibrate the speedometer for different gear ratios or wheel sizes, change rev limiters and so on. Tuning modifications may also be made so the engine will run properly with aftermarket performance accessories such as a cold air intake, exhaust headers, low restriction converters or mufflers, performance camshafts and intake manifolds. But changing the programming may prevent some of the monitors from running. Some of these programs disable the downstream O2 sensors, which will prevent the catalyst monitor from running. The fix is to return the programming back to stock (which may also require temporarily removing some of the aftermarket performance parts, too!). Gaming the system by installing a "PCM simulator" to fool the emissions test station (a trick some performance enthusiasts use on highly modified vehicles in order to "pass" emissions). If you get caught, it will result in a rejection and you will probably have to undo some or all of the performance modifications you have made to your vehicle in order to pass the test.
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OBD Monitor Not Ready
On this Innova scan tool, the OBD emissions monitor status is shown at the top of the screen. Any monitors that are flashing are NOT ready. If all of the indicators are dark , it means all have passed and the vehicle is ready for testing. Share
More OBD II Related Articles: Check Engine Light OnBoard Diagnostics More on Check Engine Lights & Diagnostics Diagnostic Tips for Trouble Codes Other Warning Lights (TEMP, OIL, ALT/GEN, BRAKES, ABS, AIR BAGS, etc.) Scan Tool Diagnostics Decoding Onboard Diagnostics TROUBLE CODE Help Understanding OBD II Driveability & Emissions Problems Zeroing in on OBD II Diagnostics Controller Area Network (CAN) Diagnostics CAN communication problem (what to do when the CAN system won't talk to your scan tool) Troubleshooting Intermittent Engine Problems Troubleshoot Engine Stalling Problems Mode 06 Diagnostics
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OBD II Emissions and Driveability Problems Copyright AA1Car.com Adapted from an article written by Larry Carley for Import Car magazine
The "Malfunction Indicator Lamp" (MIL) on 1996 and newer vehicles equipped with OBD II has created more anxiety and fear among motorists than any other piece of hardware in automotive history. If the MIL lamp suddenly comes on while the vehicle is being driven, most motorists realize something is wrong. But what? The lamp does not tell them. Nor does it give any indication if the problem is serious or not. Fortunately, many OBD II problems are relatively minor and have little impact on engine performance or reliability. But some do. The only way to know for sure what is causing the MIL lamp to come on is to plug a scan tool into the system and read the diagnostic fault code(s) to find out what is going on. If the MIL lamp comes on while driving or remains on after starting the engine, it means the OBD II system has detected a problem and is trying to alert the driver so appropriate measures can be taken. The driver should immediately check for any other warning lamps. If none are lit and the vehicle appears to be running normally, the lamp is on because something may be affecting vehicle emissions. This may or may not have an affect on driveability depending on the cause. If any other warning lamps are on (temperature, charging, oil, etc.), the problem is probably serious and requires immediate attention. Any time the MIL lamp is on, the cause should be investigated - the sooner the better. Ignoring it will not make it go away unless the fault does not recur in three consecutive drive cycles that encounter the same operating conditions, or the fault is not detected for another 40 drive cycles. If OBD II sees no further evidence of the problem it will turn off the MIL lamp and erase the code. Note: An OBD II drive cycle is not just turning the ignition key on and off or starting the engine. A drive cycle requires starting a cold engine and running it until it reaches normal operating temperature. The next drive cycle does not begin until the engine has been shut off, allowed to cool back down and is restarted again. Many OBD II vehicles have a memory backup for the PCM, so disconnecting the battery or PCM fuse will not turn the MIL lamp off or clear the codes. You have to use a scan tool to read and erase the codes. WHAT OBD II DOES & DOES NOT DO
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OBD II is primarily designed to detect emission faults, including any kind of fault that could cause emissions to exceed federal limits by 150 percent. It also monitors the following: converter efficiency, catalyst heater (if used), evaporative system, air injection system (if used), fuel trim, oxygen sensors, exhaust gas recirculation (if used), secondary air system (if used), the coolant thermostat (starting in 2000), positive crankcase ventilation system (starting in 2002) and even some A/C systems on 2002 and newer vehicles. If a fault occurs in any of these monitored systems, even if it does not cause emissions to increase 150 percent, OBD II will catch it, set a code and eventually illuminate the MIL lamp.
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With most OBD II problems, the MIL lamp does not come on right away. OBD II usually waits until the problem has occurred on two separate drive cycles before it turns on the MIL lamp. This is to reduce Learn More the number of "false warnings" that might otherwise occur if the system turned on the lamp every time it saw something amiss. So if the lamp is on, it means the problem has occurred before and has occurred again. It is not just a temporary glitch but something that needs to be diagnosed and corrected. When OBD II detects a fault, it may generate one of two types of codes. "Generic" codes, which are common to all OBD II vehicles built since 1996, have "P0" as their first two digits. "Enhanced" codes, which are special OEM codes that vary by year, make and model, have "P1" as their first two digits. All OBD II-compliant scan tools will read the generic codes, but special software is usually required to read the enhanced codes and to access other special OEM diagnostic features that may be part of the OBD II system. These include actuator tests, calibration tests and similar tests. Some of these may be available only in the factory OEM scan tool. To access codes, you have to plug a scan tool into the 16-pin J1962 connector. You will usually find it under the dash near the steering column, but on some import vehicles the connector is located elsewhere. On many Hondas, it is behind the ashtray. On BMW and VW models, it is behind trim panels. On Volvo, it is next to the hand brake. On Audi, it is hidden behind the rear seat ashtray. MISFIRE DETECTION With misfire detection, the MIL lamp may come on during the first episode if the OBD II system determines the rate of misfire is really high. On most applications, the MIL lamp will blink once per second while the misfire is actually occurring. After that, the MIL lamp may go out unless the engine had been misfiring before. OBD II will chart the rate of misfire for each cylinder along with other data such as engine speed, load and warm-up status when the first misfire was detected. It will also set a temporary fault code that will become a hard code if the same problem happens again during the next drive cycle. If the engine runs fine during the next drive cycle and does not experience any misfire, the temporary misfire code will be erased. But if the same problem recurs on two consecutive drive cycles, the temporary misfire code will become a hard code and turn on the MIL lamp. OBD II misfire codes will tell you which cylinder is misfiring. A code P30301, for example, would tell you cylinder number one is not hitting. But OBD II does not tell you why it is misfiring unless there are additional codes (such as a bad fuel injector or a lean fuel mixture code). If the misfire is ignition-related, OBD II can't tell the difference between a fouled spark plug or a grounded plug wire. But it can tell you if a distributorless ignition or coil-on-plug system has an open or grounded coil. When diagnosing misfires, it is important to use tools that allow you to actually see what is going on. A basic scan tool that reads serial data spit out by the PCM cannot tell you what the firing voltage is or what the ignition pattern looks like. Nor can it tell you if the serial data is accurate or correct. For that kind of information you need a scan tool, DVOM, graphing multimeter or oscilloscope that can look at sensor voltages directly, and/or a scan tool or scope that can also display primary and secondary ignition patterns. If the vehicle has a distributorless or coil-on-plug ignition system, you'll also need the appropriate inductive pickups to get a good ignition pattern signal from the coils. A random misfire problem (code P0300) means the misfire is jumping around from cylinder to cylinder and that multiple cylinders are experiencing a misfire problem. This is usually due to a lean fuel condition which, in turn, is being caused by a vacuum leak, an air leak in the intake manifold, dirty injectors, low fuel pressure or an EGR valve that is stuck open and
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leaking exhaust into the intake manifold. If a random misfire code is also accompanied by a P0171 code (cylinder bank 1) or P0174 (cylinder bank 2), it will help isolate the lean fuel condition to one side of the engine or the other. If you find any codes in the P0400 to P0408 range, it indicates an EGR-related problem. FUEL DELIVERY PROBLEMS OBD II monitors the operation of the fuel delivery system anytime the vehicle is driven. This includes the fuel injectors, fuel pressure, the operation of the fuel pump and pump relay, oxygen sensors, feedback fuel control loop and fuel trim adjustments. If OBD II detects any problem here, it will log a code and turn on the lamp if the same problem occurs on two consecutive drive cycles. Most vehicles use some type of short-term and long-term fuel trim adjustments to maintain the proper air/fuel ratio. OBD II keeps an eye on fuel trim and will turn on the MIL lamp if the system reaches either the minimum or maximum limit for fuel trim adjustment. Underlying problems here might include vacuum leaks, one or more dirty or leaky fuel injectors, a weak fuel pump, a bad or biased O2 sensor, etc. Any time an O2 sensor problem is suspected, the sensors response should be checked to make sure (1) it is oscillating from rich to lean, (2) that it goes to maximum voltage output (0.9 v) when the fuel mixture is rich, (3) drops to minimum voltage output (0.1 v) when the mixture goes lean, and (4) responds quickly to changes in the fuel mixture. A sluggish O2 sensor can lag too far behind changes in the fuel mixture to allow the PCM to maintain the right air/fuel ratio. The first three items can be checked with a DVOM or graphing multimeter, but measuring response time requires a scope that can measure milliseconds. Some specs say the O2 sensor should respond to changes in the air/fuel mixture in 300 milliseconds or less, while others specify a response time of 100 to 125 milliseconds. OBD II also monitors the evaporative emissions (EVAP) system, but only once during a drive cycle. The purpose here is to detect leaks that allow fuel vapors to escape into the atmosphere. OBD II does this by applying vacuum or pressure to the fuel tank, vapor lines and charcoal canister. If OBD II detects no air flow when the EVAP canister purge valve is opened, or it detects a leakage rate that is greater than that which would pass through a hole 0.040 inches in diameter (0.020 inches for 2000 and up model year vehicles, which is the size of a pin prick), the EVAP system is malfunctioning and OBD II sets a code. If you have a P0440 code indicating a fault in the EVAP system, finding the leak can be a challenge. The first place to start is the gas cap. A loose-fitting or damaged cap can allow enough air leakage to set a code. To find a vapor leak, you may need a leak detector that uses smoke and/or dye. SENSOR PROBLEMS OBD II also keeps constant watch over the operation of all the sensors (the "comprehensive component" monitor) every time the vehicle is driven. A fault here such as an open, short or loss of signal will almost always set a code. If you find a code for a particular sensor circuit, the next step is to figure out where the fault lies. Is it the sensor, a bad connector, the wiring or the PCM? A quick way to see if a sensor is providing good input is to use your scan tool to see what the PCM is seeing. If the sensor data looks good and changes normally in response to changing rpm, throttle position, load or whatever, chances are the sensor is good but the system is being affected by something else. To understand why a particular sensor code has been set if the data looks good, you have to know something about the diagnostic strategy the OBD II system uses to determine a good reading from a bad one. This is where things can get real complicated if a sensor or other component apparently checks out good, but continues to set a code. For a detailed look at the operating parameters that can set various fault codes, Click Here to view a PDF file on GM 4.6L diagnostic parameters. We heard one story about a 1997 Kia Sportage that kept turning on the MIL lamp and setting a code for the mass air flow (MAF) sensor. The MAF sensor was replaced but the code kept coming back. The MAP sensor was again replaced and the wiring checked, but the code continued to reappear. The real problem, it turned out, was actually a bad throttle position (TPS) sensor. On this particular vehicle, the OBD II system uses the TPS voltage setting to check the calibration of the MAF sensor. Because the TPS sensor wasn't reading the proper voltage at idle, the OBD II system thought the throttle was open, but the MAF wasn't reading enough air flow. So it set a code for the MAF sensor when, in fact, a bad TPS reading was causing the glitch. One time-saver here is to hook up a DVOM, graphing multimeter or oscilloscope to the sensor itself and compare the "real"
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sensor readings to what your scan tool displays using serial data from the PCM. If the values agree and are within normal ranges, you can assume the sensor, connectors, wiring and PCM are all working properly. But if the readings do not agree, there is a problem in the connector or wiring, or the PCM may be substituting bogus data for the real data. READY OR NOT?
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Other OBD II monitors include the catalyst heater, catalytic converter efficiency, secondary AIR, O2 sensor heaters, EGR system, PCV system, thermostat and A/C system (where used). These are all "noncontinuous" monitors and are not set until certain driving conditions have been met. The converter efficiency monitor, in particular, is a hard one to set and may require driving the vehicle at various speeds and loads so the OBD II system can get a good look at what is going on. for more information about OBD monitors and their ready status, Click Here.
The converter monitor compares the reading of the upstream and downstream O2 sensors to see if the converter is working efficiently. If you hook up a scope to both O2 sensors and compare the waveforms, the upstream O2 sensor should be fluctuating up and down from rich to lean with voltage readings going from 0.6 or more volts down to 0.3 volts or less. The downstream O2 sensor, on the other hand, should remain relatively flat. If the downstream O2 sensor is fluctuating in sync with the upstream O2 sensor, it means the converter is not doing much. Most converters start out at about 99 percent efficiency when new, and quickly taper off to about 95 percent efficiency after 4,000 miles or so of driving. As long as efficiency does not drop off more than a few percentage points, the converter will do a good job of cleaning up the exhaust. But if efficiency drops much below 92 percent, it will usually turn on the MIL lamp. With vehicles that meet the tougher LEV (Low Emission Vehicle) requirements, there is even less room for leeway. A drop in converter efficiency of only three percent can cause emissions to exceed federal limits by 150 percent. The LEV standard allows only 0.225 grams per mile of hydrocarbons, which is almost nothing. If you have a vehicle with a converter efficiency code, don't assume the converter is bad and replace it until you have checked for air leaks at the exhaust manifold, head pipe and converter. If possible, you should also hook up a scope and compare the upstream and downstream O2 sensor readings to verify both are working properly. One thing to keep in mind about non-continuous OBD II monitors is that they may not catch a problem until the vehicle has been driven several times and conditions are right to detect the fault. Consequently, any time you are troubleshooting an OBD II problem it is very important to use a scan tool that can tell you if all the monitor readiness flags have been set. If one or more monitors are not ready, the vehicle will have to be driven under varying speeds and loads until all the monitors are set. Then, and only then, will you get an accurate diagnosis from OBD II. Some import vehicles have readiness issues when it comes to setting all the OBD II monitors. Turn the key off on a 1996 Subaru and it will clear all the readiness flags. The same thing happens on 1996 Volvo 850 Turbos. This means the vehicle has to be driven to reset all the readiness flags. On 1997 Toyota Tercels and Paseos, the readiness flag for the EVAP monitor never will set, and no dealer fix is yet available. Other vehicles that may show a "not ready" condition for the EVAP and catalytic converter monitors include 1996-1998 Volvo, 1996-1998 Saab, and 1996-1997 Nissan 2.0L 200SX models. Once all the monitors have been set, OBD II does an excellent job of detecting faults that affect emissions. In fact, OBD II has proven itself to be so effective that some states are now using a simple OBD II plug-in check to replace I/M 240 and ASM loaded mode dyno emissions testing on 1996 and newer vehicles. So why not put OBD II to work for you? Let it do your diagnostic homework and find the problems that are causing emissions and driveability faults. MUST HAVE TOOLS FOR OBD II DIAGNOSTICS * Basic scan tool for reading and clearing OBD II generic fault codes. * Enhanced scan tool for reading OEM "P1" codes and accessing other special OEM test functions. * DVOM for measuring live sensor voltages, checking wiring continuity and grounds. * Graphing Multimeter or Oscilloscope for displaying and analyzing sensor waveforms. http://www.aa1car.com/library/ic50234.htm
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* Oscilloscope or enhanced scan tool for displaying ignition patterns.
More Articles About Onboard Diagnostics: All About Onboard Diagnostics II (OBD II) OBD Monitor Not Ready Fixing Emission Failures EVAP system EGR system PCV system Advanced Diagnostics: Mode 06 Controller Area Network (CAN) Diagnostics Exhaust Emissions Diagnosis Emissions testing update OBD II Emissions Testing Evolution of I/M 240 Driveability Diagnosis: Misfires Troubleshooting Intermittent Engine Problems Scan Tool Help TROUBLE CODES
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Engine Diagnostics: Zeroing In On OBD II Copyright AA1Car.com Adapted from an article written by Larry Carley for Import Car magazine
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Are you up to speed on OBD II diagnostics? You should be because a number of states have changed their emissions testing programs over to OBD II. Instead of doing a loaded mode emissions check on a dynamometer (I/M 240 or ASM), an OBD II check is a simple plug-in test that takes only seconds. OBD II will detect emissions problems that might not cause a vehicle to fail a tailpipe test. Consequently, emissions test failures have gone up with OBD II testing. OBD II has been required on all new vehicles sold in the United States since model year 1996, including all imports. OBD II is a very powerful diagnostic system that can give technicians a greater insight into what is actually happening within the engine control system. Early OBD II systems first began to appear on a few 1994 models, including the Lexus ES300, Toyota Camry 1MZ-FE 3.0L V6 and T100 pickup 3RZ-FE 2.7L four, plus a number of Audi, Mercedes-Benz, Volkswagen and Volvo models. In 1995, more models were added including the Nissan Maxima and 240SX. Some of these early systems are not fully OBD II compliant, meaning they may not set codes or turn on the Check Engine light for misfires, catalytic converter problems or fuel vapor leaks. Unlike earlier OBD systems that set a diagnostic trouble code (DTC) when a sensor circuit shorts, opens or reads out of range, OBD II will set codes if a fault exists that may cause emissions to rise. OBD II is primarily emissions-driven and will set codes anytime vehicle emissions exceed the federal limit by 1.5 times. It also will set codes if there is a gross sensor failure, but some types of sensor problems will not always trigger a code. Consequently, the Check Engine Light on an OBD II-equipped vehicle may come on when there is no apparent driveability problem, or it may not come on even though a vehicle is experiencing a noticeable driveability problem. The determining factor as to whether or not the Check Engine light comes on is usually the effect on emissions. In many instances, emissions can be held in check, despite a faulty sensor, by adjusting fuel trim, which the engiencomptuer does automatically. So as long as emissions can be kept below the limit, the OBD II system may have no reason to turn on the
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Check Engine Light. CHECK ENGINE LIGHT The "Malfunction Indicator Lamp" (MIL), which may be labeled "Check Engine" or "Service Engine Soon" or an ISO symbol of an engine with the word "Check" in the middle, alerts the driver when an emissions problem occurs. Depending on how the system is configured and the nature of the problem, the lamp may come on and go off, remain on continuously or flash - all of which can be very confusing because you have no way of knowing what the light means. Is it a serious problem or not? If the engine seems to be running okay, you might just ignore the light. Remember, the Check Engine light only comes on for emissions-related failures (which includes fuel and ignition, too). A separate warning light will illuminate if there are other non-emissions problems such as low oil pressure, charging system problems, etc. If the light is on because of a misfire or a fuel delivery problem, and the problem does not recur after three drive cycles (under the same driving conditions), the Check Engine light may go out. Don't think the car has healed itself because the intermittent problem may still be there waiting to trigger the light once again when conditions are right. Whether the light goes out or remains on, a code will be set and remain in the computers memory to help you diagnose the fault. With some exceptions, the OBD II warning lamp will also go out if a problem does not recur after 40 drive cycles. A drive cycle means starting a cold engine and driving it long enough to reach operating temperature. The trouble codes that are required by law on all OBD II systems are "generic" in the sense that all vehicle manufacturers use the same common code list and the same 16-pin diagnostic connector. Thus, a P0302 misfire code on a Nissan means the same thing on a Honda, Toyota or Mercedes-Benz. But each vehicle manufacturer also has the freedom to add their own "enhanced" codes to provide even more detailed information about various faults. Enhanced codes (P1 codes), which are special OEM codes for specific vehicle applications, provide additional information and often cover non-emission related failures that occur outside the engine control system. These include ABS codes, HVAC codes, air bag codes and other body and electrical codes. The second character in an OBD II will be a zero if it is a generic code, or a "1" if it is a dealer enhanced code (specific to that particular vehicle application). The third character in the code identifies the system where the fault occurred. Numbers 1 and 2 are for fuel or air metering problems, 3 is for ignition problems or engine misfire, 4 is for auxiliary emission controls, 5 relates to idle speed control problems, 6 is for computer or output circuit faults, and 7 and 8 relate to transmission problems. Generic codes that are common to all vehicle manufacturers can be accessed using any basic scan tool that is OBD IIcompliant. Unfortunately, most older scan tools will not work on the newer OBD II systems, and have to be replaced with a tool that has the proper hardware and software to read OBD II codes and other diagnostic information. Also, some scan tools do not have all the OEM codes for all makes, particularly many European applications. Accessing the OEM-specific enhanced codes may require using a dealer scan tool, which can be very expensive. MISFIRE DETECTION If an emissions problem is being caused by engine misfire, the OBD II light will flash as the misfire is occurring. But the light will not come on the first time a misfire problem is detected. It will come on only if the misfire continues during a second drive cycle and will set a P0300 series code. A P0300 code would indicate a random misfire (probably due to a vacuum leak, open EGR valve, etc.). If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Causes here would be anything that might affect only a single cylinder such as a fouled spark plug, a bad coil in a coil-on-plug ignition system or distributorless ignition system with individual coils, a clogged or dead fuel injector, a leaky valve or head gasket. The OBD II system detects a misfire on most vehicles by monitoring variations in the speed of the crankshaft through the crankshaft position sensor. A single misfire will cause a subtle change in the speed of the crank. OBD II tracks each and every misfire, counting them up and averaging them over time to determine if the rate of misfire is abnormal and high enough to cause the vehicle to exceed the federal emissions limit. If this happens on two consecutive trips, the Check Engine light will come on and flash to alert the driver when the misfire problem is occurring.
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Misfire detection is a continuous monitor, meaning it is active any time the engine is running. So too is the fuel system monitor that detects problems in fuel delivery and the air/fuel mixture, and something called the "comprehensive monitor" that looks for gross faults in the sensors and engine control systems. These monitors are always ready and do not require any special operating conditions. Other OBD II monitors are only active during certain times. These are the "non-continuous" monitors and include the catalytic converter efficiency monitor, the evaporative system monitor that detects fuel vapor leaks in the fuel system, the EGR system monitors, the secondary air system monitor (if the vehicle has such a system), and the oxygen sensor monitors. On some 2000 and newer vehicles, OBD II also has a thermostat monitor to keep an eye on the operation of this key component. The thermostat monitor will be required on all vehicles by 2002. On some 2002 model-year vehicles, there also is a new PCV system monitor, which will be required on all vehicles by 2004. The catalytic converter monitor keeps an eye on converter efficiency by comparing the outputs from the upstream and downstream oxygen sensors. If the converter is doing its job, there should be little unburned oxygen left in the exhaust as it exits the converter. This should cause the downstream O2 sensor to flatline at a relatively fixed voltage level near maximum output. If the downstream O2 sensor reading is fluctuating from high to low like the front sensor, it means the converter is not functioning. The Check Engine light will come on if the difference in O2 sensor readings indicates hydrocarbon (HC) readings have increased to a level that is 1.5 times the federal limit. For 1996 and newer vehicles that meet federal Low Emission Vehicles (LEV) requirements, the limit allows only 0.225 grams per mile (gpm) of HC - which is almost nothing. Converter efficiency drops from 99 percent when it is new to around 96 percent after a few thousand miles. After that, any further drop in efficiency may be enough to turn on the Check Engine light. We are talking about a very sensitive diagnostic monitor. The EVAP system monitor checks for fuel vapor leaks by performing either a pressure or vacuum test on the fuel system. For 1996 through 1999 vehicles, the federal standard allows leaks up to the equivalent of a hole .040 inches in diameter in a fuel vapor hose or filler cap. For 2000 and newer vehicles, the leakage rate has been reduced to the equivalent of a .020 in. diameter hole, which is almost invisible to the naked eye but can be detected by the OBD II system. Finding these kinds of leaks can be very challenging. According to one expert, you can find a .040 in. leak with an ultrasonic leak detector but not a .020 in. leak. For such a small leak, you need a smoke or dye-type detector. READINESS MONITORS An essential part of the OBD II system are the "readiness monitors". These are self-tests the OBD II system runs to make sure everything is functioning normally. When a test runs and pases without any faults, the OBD II system runs the next monitor and the next until all have completed. This may take some time because some monitors require specific driving conditions before they will run. Also, if a fault is found during any test, it may prevent subsequent monitors from completing. The misfire detection, fuel system and continuous system monitors are active and ready all the time, but the non-continuous monitors require a certain series of operating conditions before they will set - and you cannot do a plug-in OBD II test unless all of the monitors are ready. To set the converter monitor, for example, the vehicle may have to be driven a certain distance at a variety of different speeds. The requirements for the various monitors can vary considerably from one vehicle manufacturer to another, so there is no "universal" drive cycle that will guarantee all the monitors will be set and ready. As a general rule, doing some stop-and-go driving around town at speeds up to about 30 mph followed by five to seven minutes of 55 mph plus highway speed driving will usually set most or all of the monitors (the converter and EVAP system readiness monitors are the hardest ones to set). So if you are checking the OBD II system and find a particular monitor is not ready, it may be necessary to test drive the vehicle to set all the monitors. The Environmental Protection Agency (EPA) realized this shortcoming in current generation OBD II systems. So, when it created the rules for states that want to implement OBD II testing in place of tailpipe dyno testing, it allows up to two readiness flags to not be set prior to taking an OBD II test on 1996 to 2000 vehicles, and one readiness flag not to be set on 2001 and newer vehicles. Some import vehicles have known readiness issues. Many 1996-98 Mitsubishi vehicles will have monitors that read "not ready" because setting the monitors requires very specific drive cycles (which can be found in their service information). Even so, these vehicles can be scanned for codes and the MIL light without regard to readiness status. On 1996 Subarus, turning the key off will clear all the readiness flags. The same thing happens on 1996 Volvo 850 Turbos.
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This means the vehicle has to be driven to reset all the readiness flags. On 1997 Toyota Tercel and Paseo models, the readiness flag for the EVAP monitor will never set, and no dealer fix is yet available. Other vehicles that often have a "not ready" condition for the EVAP and catalytic converter monitors include 199698 Volvos, 1996-98 Saabs, and 1996-97 Nissan 2.0L 200SX models. OBD II TEST An official OBD II emissions test consists of three parts: 1. An inspector checks to see if the MIL light comes on when the key is turned on. If the light does not come on, the vehicle fails the bulb check. 2. A scanner is plugged into the diagnostic link connector (DLC), and the system is checked for monitor readiness. If more than the allowed number of monitors are not ready, the vehicle is rejected and asked to come back later after it has been driven sufficiently to set the readiness flags. The scanner also checks the status of the MIL light (is it on or off?), and downloads any fault codes that may be present. If the MIL light is on and there are any OBD II codes present, the vehicle fails the test and must be repaired. The vehicle also fails if the DLC is missing, has been tampered with or fails to provide any data. 3. As a final system check, the scanner is used to command the MIL lamp on to verify it is taking commands from the onboard computer. If the OBD II light is on, or a vehicle has failed an OBD II emissions test, your first job is to verify the problem. That means plugging into the OBD II system, pulling out any stored codes and looking at any system data that might help you nail down what is causing the problem. Long-term fuel trim data can provide some useful insight into what is going on with the fuel mixture. If long-term fuel trim is at maximum, or you see a big difference in the numbers for the right and left banks of a V6 or V8 engine, it would tell you the engine control system is trying to compensate for a fuel mixture problem (possibly an air leak, dirty injectors, leaky EGR valve, etc.). OBD II also provides "snap shot" or "freeze frame" data, which can help you identify and diagnose intermittent problems. When a fault occurs, OBD II logs a code and records all related sensor values at that moment for later analysis. Once you have pinpointed the problem and hopefully replaced the faulty component, the final step is to verify that the repair solved the problem and that the OBD II light remains off. This will usually require a short test drive to reset all the readiness monitors and run the OBD II diagnostic checks. For a detailed look at the operating parameters that can set various fault codes, Click Here to view a PDF file on GM 4.6L diagnostic parameters.
OBD II TOOLS & EQUIPMENT You cannot work on OBD II systems without some type of OBD II-compliant scanner. Choices here include: Aftermarket scan tools with the appropriate software and J-1962 16-pin universal diagnostic connector. If you already own an up-to-date scan tool, all you may need is a new software update and OBD II wiring connector. On the other hand, if your scan tool is more than four or five years old, it may not be OBD IIupgradable. Before you upgrade or replace a scan tool, make sure the new tool will provide the dealer-enhanced codes as well as the generic codes for the import vehicles you service most often. This usually is not a problem with the Asian makes, but it can be a problem with the European makes. Dealer scan tool. The main advantage you will enjoy with a dealer scan tool is access to all of the same data and capabilities as the car dealers, which often includes enhanced diagnostic capabilities and two-way communication. The drawback with a dealer scan tool is that it can only be used on a particular make of vehicle, unlike aftermarket scan tools which work on a variety of makes. Cost is also a major hurdle, with some dealer scan tools costing several times as much as a typical aftermarket scan tool. OBD II code reader. In recent years, a number of equipment suppliers have introduced relatively low cost (under $200) code
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OBD II Engine Diagnostics
readers that can be used to read and clear OBD II codes. Such tools lack many of the more advanced diagnostic features of a scan tool, but at least allow you to retrieve codes and check monitor readiness flags. Scanner software for a laptop personal computer (PC), Palm or Handspring Visor personal digital assistant (PDA). Software and wiring connectors are available to convert a laptop PC or PDA into a basic scan tool. You can read and clear codes, read and display system data in numeric or graphic formats, check readiness monitors, capture snapshot data and more depending on the capabilities of the software. If you already own a PC or PDA, going this route may be a more affordable alternative to upgrading or buying a new scan tool. PC and PDA software packages typically sell for around $350 and include the J-1962 16-pin universal diagnostic connector. If you are considering purchasing a PDA, look for one that has an expansion slot and sufficient memory to handle future upgrades. If a vehicle has an OBD II EVAP code (P0400 series codes), you may need some type of leak detection equipment to find the cause. Choices here include ultrasonic leak detectors that listen for sound waves produced by air or vapors escaping through an opening, smoke detectors that generate smoke which allows leaks to be spotted visually, and dye detectors that use a visible or ultraviolet dye to reveal leaks. ADVANCED DIAGNOSTICS For advanced diagnostic work, a digital oscilloscope is a great tool for displaying sensor waveforms. Momentary faults that happen too quickly for a conventional voltmeter or even the OBD II system to detect can often be revealed by observing and comparing waveforms. Do not expect to hook up a scope and start making a diagnosis right away because learning how to use a scope takes some time and experience. You need to learn how to distinguish good waveforms from bad ones - which means looking at vehicles that do not have problems as well as ones that do. The International Automotive Technicians Network (www.iatn.com) maintains an online library of waveforms for members that is a great resource.
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Emissions Testing
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Emissions Testing Copyright AA1Car Emissions testing has been a controversial subject ever since its inception. Though most opinion polls show widespread public support for clean air in general, few motorists show any enthusiasm for emissions testing when it involves their own vehicles. And most are reluctant to spend money on emission-related maintenance or repairs. As long as most vehicles pass an emission test, most people will go along with a program, pay a reasonable test fee and tolerate waiting in line 20 to 30 minutes once eery year or two to have their vehicle tested. But when their vehicle fails an emissions test, their attitude often becomes angry and resentful. An emissions failure creates stress and anxiety because of what comes next. A failure means finding a shop with technicians who are competent enough to do emission repairs, making a service appointment, being without a vehicle for half a day or more, having to spend up to several hundred dollars or more on emission repairs they may not even believe are really necessary, and then taking the vehicle back to the inspection station for retesting. And if the vehicle fails the retest? They feel even more frustration and anger as they bounce back and forth between the repair facility and test station. Consequently, there has been a lot of public backlash against emission test programs that are too stringent or fail too many vehicles. A growing number of people today are questioning the value of emissions testing, and wonder if it is making any significant difference in reducing air pollution. U.S. Environmental Protection Agency (EPA) statistics show that air quality is improving in most areas of the country, but the data fails to show a direct link between the reductions in pollution from mobile sources (vehicles) and emission testing. Some areas that have no inspection/maintenance (I/M) programs have shown just as much improvement in air quality as areas that do emissions testing. Most of the reduction in emissions from mobile sources is being attributed to changes in the vehicle population. As older vehicles are replaced by newer, cleaner running vehicles, the amount of pollution from mobile sources has gone down and will continue to decline as time goes on. Not only are new vehicles much cleaner, they also stay cleaner for a longer period of time. Even so, older vehicles (10 years old or more) continue to be a significant part of the vehicle population and represent a major source of pollution. Consequently, periodic emission testing is seen as a necessary means of policing these older vehicles.
DOES THE PUBLIC SUPPORT EMISSIONS TESTING? According to the National Center of Vehicle Emissions Control & Safety (NCVECS), Colorado State University, various issues confront vehicle emissions testing today: Little political or public support for emissions testing. Lax standards and poor enforcement of existing I/M programs. Lack of credibility that existing I/M programs are having an impact on air quality. Reluctance to implement effective enhanced I/M programs in non-attainment areas. Political pressure on the EPA to be more "flexible" in accepting various emission testing alternatives. Rising costs of administering and conducting enhanced emissions testing. Less need to inspect newer vehicles. Adding OBD II checks into existing I/M programs, or substituting OBD II checks for tailpipe tests on 1996 and newer vehicles. Technician training and competency.
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Emissions Testing
History of Emissions Testing Legislation
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In 1990, Congress amended the Clean Air Act. The revisions required areas that did not meet national ambient air quality standards (NAAQS) to implement either basic or "enhanced" vehicle I/M emissions testing programs, depending upon the severity of the area's air quality problem. The act also required that metro areas with populations of more than 100,000 implement enhanced I/M emissions testing regardless of their air quality designation. EPA, in turn, was required to develop standards and procedures for emissions testing. On November 5, 1992, EPA issued its original rule establishing minimum performance and administrative requirements for states developing air quality implementation plans. The EPA said areas that needed enhanced emissions testing would have to use their new I/M 240 test procedure. I/M 240 was controversial for several reasons. One was that it specified centralized testing. The EPA said the use of "test only" facilities administered by an independent contractor would eliminate any conflicts of interest (fraud) in shops that both test and repair vehicles. California garage owners balked at the requirement, and eventually forced the EPA to accept a hybrid decentralized program in their state. The I/M 240 requirement also specified loaded mode testing for measuring transient emissions on a special dynamometer, as well as checking NOx emissions and doing an evaporative system purge and pressure test. The I/M 240 test was based on procedures the EPA had already developed for certifying new vehicle emission compliance. This, in turn, required a lot of expensive equipment as well as the use of a trained operator to follow a prescribed drive cycle while the vehicle was on a dyno.
In 1995, however, the National Highway System Designation Act was passed. The act included provisions that specifically barred the EPA from mandating I/M 240 exclusively for enhanced emissions testing. So the EPA was forced to adopt a more flexible posture toward alternative I/M test programs. States are still required to meet air quality standards, but now have a much wider range of options for meeting those standards. These include scrapping programs for taking older vehicles off the road, the use of onboard diagnostic system (OBD) testing for verifying emissions performance, the use of decentralized I/M programs, roadside testing and various enhanced test procedures such as acceleration mode testing (ASM) and others that have been developed as alternatives to I/M 240. For example, it is currently possible for some areas to design emissions testing programs that meet the required enhanced I/M performance standard without any tailpipe testing at all, using a combination of alternative evaporative system pressure testing methods, onboard diagnostic system checks, and visual anti-tampering inspections. Many states are now using a process called "clean screening" to simplify emissions testing. The goal here is not to identify high polluting vehicles for repairs, but to identify especially clean vehicles, which can be exempted from routine testing. Some states now exempt new cars from emissions testing until they are two or more years old, and then only require testing every two years thereafter.
ENHANCED EMISSIONS TESTING I/M 240 has pretty much disappeared due to its cost and complexity. Most states are now using a simple plug-in OBD II emissions test. The onboard diagnostic system in late model vehicles does an excellent job of monitoring emissions compliance. It will set diagnostic trouble codes (DTCs) and turn on the Check Engine Light if a problem occurs that may cause emissions to exceed federal limits by a specified amount (typically 1.5X). For the latest information on current state emissions testing programs, see OBD Program Status or Vehicle Emissions I/M Programs. States that implemented some type of enhanced emissions testing (I/M 240 or similar tests) to measure tailpipe emissions during transient operating modes on a dyno, or acceleration simulation mode (ASM) tests, have mostly found that a plug-in OBD II check works just as well while eliminating the risks of placing a motorist's car on a dyno and running it at highway speeds. As the vehicle population continues to get cleaner, and new vehicles meet even low emission vehicle (LEV) and ultra-low emission vehicle (ULEV) standards, the cost of vehicle emissions testing programs will likely come under close scrutiny by legislators. Some areas may opt to phase out their annual or biennial emissions inspections and replace them with roadside sniffers and profiling to zero in on problem vehicles. California is looking at standards for what may eventually become OBD III technology. The next generation OBD system could use wireless cell phone technology in conjunction with the onboard diagnostic system to report a vehicle's emission status to the state. As long as the vehicle's emissions are in compliance, there would be no need to bring it in for a test (saving motorists and the state time and money). But if the vehicle developed a problem, it would then have to be repaired and/or tested to bring it back into compliance.
Emissions Test Standards As we move forward, the amount of pollutants allowed in the exhaust continues to be reduced. That includes carbon monoxide (CO), unburned hydrocarbons (HC), formaldehyde (HCHO), non-methane organic gases (NMOG), oxides of nitrogen (NOx) and particulate matter (PM). Here are some current and future federal and California emission standards:
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Emissions Testing
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Emissions Testing: Exhaust Analysis
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Did your vehicle fail an emissions test? Emissions testing is an inconvenience and a hassle, but it is required in many areas. Emissions testing helps minimize the impact of automotive pollutants on our environment. Emissions also affects engine performance and fuel economy, so a failure may also mean your engine is not getting peak fuel economy or performance. The law says the vehicle owner is responsible for having their vehicle repaired if it fails an emissions test. Many states have waiver provisions that limit the amount of money you have to spend in an attempt to repair an emissions failure. Even so, the dollar amount may be as high as $450 depending on the model year of the vehicle. And, if tampering is involved (emission controls have been removed or rendered inoperative), there may be no waiver limit on the repairs!
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The fix for an emissions problem may only require some relatively minor adjustments or repairs (changing an air filter or spark plugs, fixing a vacuum leak, replacing a defective sensor, etc.), or it may require more extensive repairs. An engine with a burned exhaust valve, for example, is going to blow hydrocarbons out the tailpipe until the head is pulled and the valve problem is fixed. The same goes for other internal engine problems such as broken rings, cracked pistons, worn or scored cylinders, etc. that require major repairs. Many emission failures are relatively simple to diagnose because the cause is fairly obvious. Other times, the cause is less obvious and not so easy to diagnose. Sometimes the cure can only be found in a vehicle manufacturer's technical service bulletin (TSB). Some of these problems turn out to be calibration glitches in the engine management software that requires flash reprogramming the powertrain control module (PCM) or replacing other components. To find these kinds of emission failures, you need access to a TSB database such as that available through a computerized repair information system such as AlldataDIY.com. Elevated hydrocarbon (HC) emissions usually indicate ignition misfire due to fouled spark plugs or a bad plug. But high HC emissions can also be caused by burned exhaust valves (check compression), lean misfire (check for vacuum leaks, low fuel pressure or dirty injectors), or rich fuel conditions (fuel saturated carburetor floats, excessive fuel pressure, leaky injectors or a dead O2 sensor). High carbon monoxide (CO) emissions are a telltale sign of a rich fuel mixture. On older carbureted vehicles, fuel-saturated plastic floats, incorrect float settings, leaky power valves and misadjusted chokes are often responsible for the rich mixture. On newer vehicles with feedback fuel controls and fuel injection, leaky injectors, excessive fuel pressure and sluggish or contaminated O2 sensors are all possibilities to investigate. Harder to diagnose are elevated oxides of nitrogen (NOX) emissions. Causes here may include a defective EGR valve, EGR vacuum solenoid or motor, plugged EGR ports in the manifold, over-advanced ignition timing or engine overheating. In areas that do I/M240 loaded mode dyno emissions testing, or use an OBD II plug-in emissions check, problems with the evaporative emission control system (EVAP) can also cause your vehicle to fail. A leaky gas cap is an often-overlooked
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Emissions Testing: Exhaust Analysis
cause for leaking fuel vapors into the atmosphere. EMISSIONS FAILURE Since loaded mode testing is the most demanding in terms of emissions performance, let's see what happens when a vehicle fails this type of emissions test. A loaded mode test uses a dynamometer to simulate actual driving conditions. During the test, pollutants are monitored during idle, acceleration, cruise and deceleration. The pollutants are typically measured in grams per mile (gpm) rather than percentage of concentration (%) or parts per million (ppm) which makes it hard to translate ordinary 4 and 5-gas analyzer readings into gpm readings. Software is available that can do a fairly accurate conversion using additional inputs such as vehicle weight and engine displacement. Without the proper software, there's no way to know if a vehicle's HC, CO and NOX readings are within the required gpm limits or not. In any event, the motorist is usually given a printed form that indicates which portion of the test their vehicle failed and by how much. The form may also provide additional diagnostic readings such as carbon dioxide (CO2) and/or oxygen. Some forms also plot the data on a graph so you can more easily see which part of the test produced the highest levels of pollution. In an I/M 240 test, the vehicle is run on a dynamometer for up to 240 seconds. The drive cycle is broken into two phases. Phase One lasts 93 seconds. The test starts at idle, includes two minor accel/decel curves before attaining a "low speed cruise condition," then decels to a stop. Phase 2 includes three high speed cruises: One at 47 mph and two cruises in the 54 to 56 mph range. During the drive cycle, the emissions are gathered and recorded second-by-second. The I/M 240 software calculates the total amount of HC, CO and NOX produced for each portion of the test. If emissions are low enough during the first 30 seconds of the test, the test may be ended early with a "fast pass" issued. But if emissions are high or borderline during the first part of the test, the test will go the full duration to determine an ultimate pass or fail grade. In states that use a simpler "hump" drive cycle, the vehicle accelerates at a given rate from idle to a predetermined cruising speed (30 to 33 mph), holds at cruise for a given number of seconds, then decels back to idle. There are some preliminary checks that should be made any time a vehicle with an oxygen sensor feedback control system fails an emissions test: Always verify that basic engine compression, vacuum, fuel pressure and ignition timing are normal; The air cleaner is clean and unobstructed; The engine is running at normal temperature; All emission control devices are installed and appear to be connected properly; and Is the "Check Engine" light on? If the light is off, cycle the ignition to make sure the bulb is not burned out. If the light is on, there are stored trouble codes that can help you make your diagnosis. If the computer doesn't use LEDs to display the code, a scan tool or other diagnostic tester will be needed to access the codes. On 1995 and newer vehicles with OBD II, the OBD II system is usually capable of detecting most of the problems that can cause an emissions failure. If the light is off, check for history codes that may reveal a part problem. IDLE EMISSIONS A vehicle that has sharply elevated HC or CO emissions at idle will usually have a noticeable misfire and/or rough idle. The most likely causes here would be: Fouled spark plug(s); Shorted spark plug wire(s) or defective plug boot(s); Vacuum leak; EGR valve stuck open;
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Burned exhaust valve; Misadjusted throttle body air/fuel mixture; or Misadjusted carburetor idle mixture. An extremely rich fuel condition can also cause elevated HC and CO at idle, while an extremely lean condition will only cause HC to rise abnormally. A leaky EGR valve can act like a vacuum leak and cause a lean misfire at idle. HC and CO will be somewhat higher as a cold engine warms up because the fuel system may still be running in open loop. Until the engine reaches a predetermined temperature and/or the oxygen sensor gets hot enough to produce a good signal, the PCM will supply a relatively rich mixture while the system is in open loop. A faulty thermostat that is stuck open or a defective coolant sensor may prevent the system from going into closed loop. NOX emissions are always lowest during idle and decel because that is when engine load and combustion temperatures are lowest.
ACCELERATION EMISSIONS During acceleration, the engine momentarily drops out of closed loop and receives a richer fuel mixture for more power. During this time (depending on the system), the MAP or Airflow Sensor and the TPS sensor play critical roles in controlling the fuel mixture. Most fuel-injected engines have either a throttle position sensor or switch that indicates when the engine is at idle. When this device indicates that the engine is no longer at idle, the on time of the injectors is increased to temporarily richen the fuel mixture. The same thing happens any time the engine comes under load and manifold vacuum drops. The MAP sensor tells the computer the engine is under load, and the computer responds by adding more fuel. It is normal to see some spikes in CO during acceleration, but unusually high CO readings indicates that the fuel mixture is too rich. Possible causes might include: Flooded charcoal canister or a leaky purge valve; Leaky power valve (older carbureted engines); Defective mass airflow (MAF) sensor, manifold absolute pressure (MAP) sensor, or vane airflow meter (VAF); or Defective throttle position sensor. If the feedback fuel control system is working properly and there are no apparent sensor or purge valve problems, the catalytic converter may be contaminated or not functioning. Elevated HC readings during acceleration indicate ignition misfire under load. The causes could be: Defective knock sensor; Weak ignition coil(s); Excessive resistance in spark plug wires; Arcing inside the distributor cap; Worn, fouled or incorrectly gapped spark plugs; Over-advanced ignition timing; or
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Lean air/fuel mixture. NOX readings will rise sharply during acceleration and will peak a few seconds after the cruising speed is reached. If the EGR system fails to recirculate exhaust back into the intake manifold, combustion temperatures will rise causing an increase in NOX. The higher temperatures may also cause some detonation (spark knock) to occur, which may be audible when the engine is under load. Causes of elevated NOX emissions during acceleration include: Defective EGR valve; Leaky EGR valve plumbing or control solenoid; Carbon deposits in EGR manifold passageways; Carbon buildup on pistons and in combustion chamber; Over-advanced ignition timing; Defective knock sensor; Engine overheating (check thermostat, fan, coolant level); Exhaust restrictions. CRUISE EMISSIONS At cruise, the engine is lightly loaded and running at high rpm. Under these conditions, HC and CO should be low if the oxygen sensor and feed back control system are working properly, and the catalytic converter is in good condition. High CO readings during cruise indicate a rich fuel condition. Causes here may include: Defective O2 sensor; Exhaust leaks upstream of the O2 sensor (check manifold gaskets and air plumbing connections); Defective AIR pump or diverter valve (also loose or damaged air pump plumbing); Defective MAP, MAF or VAF sensor; Float level and operation (older carbureted engines); and Power valve operation (older carbureted engines). High HC during cruise would indicate a steady misfire or loss of compression (leaky exhaust valve). DECEL EMISSIONS When decelerating, the engine will typically either lean out the fuel mixture or shut the fuel off completely (some fuel-injected engines). The computer typically uses inputs from the Vehicle Speed Sensor, TPS, MAP and/or Airflow sensors, and engine rpm to determine when this occurs. When the throttle closes and manifold vacuum shoots up, the computer cuts back on the fuel. Normally, HC, CO and NOX emissions drop during deceleration because the engine is no longer under load and is receiving little or no fuel. If CO emissions remain high during deceleration, the engine is receiving too much fuel. Causes may include: Defective decel valve (older carbureted engines); Leaky fuel injectors; and Faulty VSS, TPS, MAP or airflow sensor.
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EVOLUTION OF I/M240 LOADED MODE VEHICLE EMISSIONS TESTING
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I/M240: Load Mode Emissions Testing Copyright AA1Car I/M 240 is an "enhanced" inspection/maintenance vehicle emissions testing program for improving air quality in areas that fail to meet the federal government's ambient air quality standards. The test is similar to the Federal Test Procedure (FTP) that auto makers use to certify new vehicle emissions. A key feature of the I/M 240 test procedure is the use of a special inertia dynamometer to simulate vehicle loads at various speeds during a 240second drive cycle that includes acceleration, deceleration and cruise modes. The test can catch emission problems that often escape notice during a simple idle emissions test, but it requires a trained operator to "drive" the vehicle while it is on the dyno, and the special dyno that is required is very expensive. A single I/M 240 test lane can cost upwards of $150,000 or more!
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The I/M 240 test also measures oxides of nitrogen (NOx) in the exhaust, and uses a special continuous gas collection system rather than a partial gas sampling system to analyze the exhaust. The equipment monitors the vehicle�s emissions for the duration of the test, then calculates the average emissions and displays the results in grams per mile for NOx, CO and HC (rather than the more familiar parts per million or percent of concentration).
The I/M 240 test also requires an "evaporative purge flow test" while the engine is running to measure the flow rate of the charcoal canister purge valve, and an engine off pressure test of the evaporative emission control system to check for fuel vapor leaks. Other elements of the program include centralized vehicle testing by a single contractor, required training and certification for technicians who do emission repairs, and higher repair waivers (up to $450) for vehicles that fail to pass the test.
FOR BETTER OR WORSE In areas that do not meet federal air quality standards, the U.S Environmental Protection Agency (EPA) has dictated that these areas must use some type of enhanced emissions testing such as I/M 240 or a similar loaded mode test method, or use an OBD II plug-in test (for 1996 and newer vehicles). Areas that do not comply suffer the consequences (withholding of federal highway funds, withholding environmental building permits, invoking various injunctions, fines, etc.).
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EVOLUTION OF I/M240 LOADED MODE VEHICLE EMISSIONS TESTING Those who are opposed to I/M 240 (and there are many!) say: The required test equipment is way too expensive and unnecessary. The same results can be obtained with a less costly constant load dyno using an "Acceleration Test Mode" (ASM) test procedure. ASM testing applies a 50% load at 15 mph, and a 25% load at 25 mph, and uses a less expensive emissions analyzer. The drive cycle part of the test is too complicated, and the results can vary depending on how well the test operator follows the driving trace. The cut points are too strict, and too many vehicles fail the test. The failure rate is also influenced by the weather. Hot weather causes more failures to occur than cooler weather. Many NOx failures are difficult to diagnose and repair, which makes for unhappy customers (& voters) when vehicles cannot be repaired properly (high retest failure rates). Many failures are also expensive to fix. Existing programs have had little if any environmental impact. Critics of Colorado's I/M 240 program cite a study by the Colorado Dept. of Public Health and Environment (CDPHE) that found the state's I/M 240 program had virtually no impact on air quality. During the program's first year of operation (1995), ambient carbon monoxide levels were actually worse than the five previous year's average, and showed no reduction in median CO levels over the five year period.
The EPA, by comparison, claims I/M 240 can potentially reduce HC and CO emissions by 5 to 30%, and NOx emissions up to 10%
A NEW POSTURE In 2000, the EPA recognized the objections to I/M 240 and decided to allow a more flexible approach to enhanced emissions testing. The EPA decided it would allow states to choose whatever enhanced test procedure works best for their situation be it I/M 240, ASM testing on a constant speed dyno or some other loaded test procedure that also includes NOx and evaporative emissions. The latest twist in the evolution of I/M 240 is the addition of an OBD II plug-in test for 1996 and newer vehicles. The OBD II test uses the vehicle's own computer to monitor emissions compliance. There is no actual measurement of tailpipe emissions, nor is the vehicle placed on a dyno. Instead, a computer is plugged into the vehicle's diagnostic connector to see (1) if the OBD II sysem is functioning properly, (2) that there are no stored fault codes and (3) that the Malfunction Indicator Lamp (MIL) is not on. If the OBD II system has run all its self-checks and the vehicle is in emissions compliance, it passes the plug-in test. But if the MIL lamp is on, the vehicle fails the test and may be subjected to a repeat plug-in test or some type of loaded mode emissions test on a dyno. As I/M 240 and the whole issue of emissions testing continues to evolve, it is possible that advances in onboard diagnostics may make the need for periodic emissions testing unnecessary, at least for newer vehicles. The proposed next-generation OBD III might include an onboard transmitter that would report a vehicle's emission performance to a roadside receiver or central office (GM's OnStar system can do that now!). If an emissions violation occurs, the vehicle rats on itself and the owner receives a summons requiring them to report to the nearest test facility within so many days for an emissions test. Talk about Big Brother under your hood!
A SHORT HISTORY Maine was the first state to make the I/M 240 plunge back in 1995. The state and repair industry were both ill-prepared to handle the rigors of I/M 240 testing, and the public backlash that followed forced the governor to cancel the program. Colorado was the next to adopt a modified I/M 240 program, also in 1995. Other states with I/M 240 programs include Arizona, Wisconsin, Ohio, Indiana and Maryland. I/M 240 programs are also coming in Washington D.C. (January 1999), Illinois (January 1999) and Missouri. ASM enhanced test programs are used in California, Delaware, Georgia, New Jersey, Virginia and Connecticut. Pennsylvania has used ASM testing in the Philadelphia area, and other areas. New York, Massachusetts and Rhode Island use a NYTEST239 test procedure, which is a sort of hybrid version of ASM and I/M 240 testing that includes transient mode testing on a dyno but uses a less costly exhaust sampling system.
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TEST APPROACHES Though some states still use a simple idle test to check emissions, the ones that do not meet air quality standards mostly use some type of enhanced loaded mode dyno emissions testing or the new OBD II plug-in test. One trend that is helping to minimize the inconvenience of having to take an emissions test is extending the time period between tests for newer, low mileage vehicles. In some states, testing is only required every other year and may not be required at all until a vehicle is four years old.
THE CALIFORNIA MODEL Recent changes in California's Smog Check II program are a good indication of the direction that other states forced to adopt enhanced emissions testing may follow. When the federal Clean Air Act was amended in 1990, the U.S. Environmental Protection Agency initially mandated a centralized, state-run enhanced vehicle emissions testing program (I/M240) that would have eliminated privately-owned Smog Check stations (a $480 million per year industry in California). California negotiated an alternative plan with the EPA that would achieve the same reductions in vehicle emissions without such draconian measures. The new emissions testing program enhancements were enacted into law in 1994 and approved by the EPA on September 26, 1996. Subsequent
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EVOLUTION OF I/M240 LOADED MODE VEHICLE EMISSIONS TESTING
legislation has further refined the Smog Check II program to include the following elements: As of June 8, 1998, California's smoggiest urbanized regions that did not meet federal or state air quality standards for ozone and carbon monoxide went to enhanced emissions testing on a dyno. The tests included oxides of nitrogen (NOx) for the first time. Enhanced areas include all of Orange County, southern Ventura County, western San Diego County, most of Los Angeles county, parts of Riverside and San Bernardino counties, and the urbanized areas of Sacramento, Fresno, Stockton, Modesto, Bakersfield, Davis, Vacaville, Palm Springs, and Hemet-San Jacinto. In less smoggy "basic areas" enhanced emissions testing is not required and the existing biennial two-speed idle test at licensed test-and-repair stations remains the same as before. Basic emissions testing is required for vehicles that are being sold or are being registered in California for the first time. New Test Equipment. In areas that require enhanced testing, equipment meeting BAR97 specifications and a dynamometer are required. The BAR97 Emissions Inspection System (EIS) for Acceleration Simulation Mode (ASM) testing consists of a 5-gas analyzer, other hardware, software, a fuel cap tester, and a dynamometer with restraints. Test station technicians are also required to have a Digital Storage Oscilloscope (DSO) to help diagnose emissions system problems, and an "Advanced Emissions Specialist" (EA) license. The dyno is used primarily for checking NOx emissions. To get accurate NOx readings, the engine must be under load to produce the high combustion temperatures that form NOx. The only problem with using a dyno is that some all-wheel drive and four-wheel drive vehicles cannot be driven on a two-wheel dyno, nor can some vehicles with traction control systems. These vehicles will be exempt from the enhanced emissions test but must still pass a two-speed idle test. Test results are transmitted electronically to the California Department of Motor Vehicles. Eliminating paper Smog Check certificates should reduce the potential for fraud. Targeting Gross Polluters. A "gross polluter" is a vehicle that far exceeds allowable emissions levels for a particular model. Gross Polluters represent up to 15% of California vehicles, but are responsible for more than half of the state's vehicular smog. Gross polluters must be repaired and have those repairs verified (and emissions certified) at a Test-Only station. California will use computer modeling to identify vehicles that fit the "high emitter profile" so the owners can be notified that they have to take their vehicles to a Test-Only station for testing. Test-Only Stations are privately-owned Smog Check stations licensed by the Department of Consumer Affairs/Bureau of Automotive Repair (DCA/BAR) to inspect and certify vehicles (including gross polluters), but they do not fix emission problems. Repairs can be performed at "Gold Shield Guaranteed Repair" stations which are licensed Smog Check facilities that meet high performance standards and guarantee the repairs they make on gross polluters. Remote Sensing Devices (road side sniffers) may also be used to catch gross polluters. Such devices use an infrared beam to identify gross polluters and a camera snaps a picture of the vehicle's license plate. Help for poor folks. If a vehicle fails a Smog Check inspection, but the owner cannot afford to make the repairs, the owner may be granted a "repair cost waiver" if the owner first pays for at least $450 in emissions-related repairs at a licensed repair station. This waiver is good for two years, and only one waiver will be issued while the motorist owns the vehicle. There is also an "economic hardship extension" for qualified low-income motorists. Like the Repair Cost Waiver, the extension is valid for two years and may be obtained only once during a motorist's ownership of a vehicle. However, to obtain an extension, motorists must spend $250 on emissions-related repairs at a licensed Smog Check station, or have an estimate from a licensed Smog Check station showing that a single repair would cost more than $250. Motorists must also verify their household income, which must be at or below 175% of the federal poverty level (about $29,000 a year for a family of four). Neither the repair cost waiver nor the economic hardship extension can be obtained if the vehicle has a tampered emissions system, is being registered for the first time in California, is being sold, or was issued a waiver or extension in the previous Smog Check inspection. California also offers "low income repair assistance" to help low-income motorists pay for emissions-related repairs. The program will help pay for vehicle repairs that are cost-effective and maximize clean air benefits. The motorist must make a $250 co-payment, with the state contributing an additional amount not to exceed $450. Repairs must be performed at a Gold Shield station. Exempt vehicles: Cars built in model year 1973 and earlier are exempt from all aspects of the Smog Check Program. Also, cars four model years old and newer are exempted from the biennial requirement, but still must have Smog Checks performed when the vehicle is sold or being registered for the first time in California.
THE FUTURE Enhanced emissions testing with a vehicle under load on a dyno (either steady speed or transient) will continue for older vehicles (pre-1996), as will NOx testing and evaporative emission checks on many vehicles (where required). The question is will all of this make a significant difference in improving overall air quality? When much of the Third World thumbs its nose at even the most rudimentary efforts to reduce pollution, and rain forests are being burned at an alarming rate, one cannot help but question the cost effectiveness of emissions testing in the overall scheme of things. Certainly, doing something is better than doing nothing. Someday OBD III and roadside sniffers may eliminate the need for periodic emissions testing altogether. But regardless of what happens, there will be an ongoing need for emissions diagnose and repair. Why? Because emissions is the end result of engine performance. If an engine pollutes, it probably runs bad, too. So a clean tailpipe is a good indication of a good running, fuel efficient engine. For the latest information on current state emissions testing programs, see OBD Program Status, or Vehicle Emissions I/M Programs.
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Current Emissions Testing Standards As we move forward, the amount of pollutants allowed in the exhaust continues to be reduced. That includes carbon monoxide (CO), unburned hydrocarbons (HC), formaldehyde (HCHO), non-methane organic gases (NMOG), oxides of nitrogen (NOx) and particulate matter (PM). Here are some current and future federal and California emission standards:
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. We've come a long way in our struggle to reduce air pollution from cars. Today's vehicles are the cleanest ever, and getting cleaner all the time. Advances in emission control technology have cut hydrocarbon (HC) and carbon monoxide (CO) emissions to almost nothing. Oxides of nitrogen (NOX) emissions, which also contribute to smog, have also been reduced to a fraction of what they once were. Evaporative emissions from the fuel system have also been eliminated, and gasoline has been reformulated to burn cleaner and reduce emissions even more. Consequently, today's cars are probably 99% cleaner than their pre-emission counterparts of 30 years ago. As the next level of emission standards are phased in for cars, light trucks and heavy trucks, emissions will further drop. Reduced sulfur content in fuels and "Tier II" emission regulations should lower vehicle emissions another 20 to 25%. Today's emission controls have done an amazing job of minimizing pollution from motor vehicles. But one thing emission control technology has not been able to change is the basic chemistry of combustion itself. The issue now is Carbon Dioxide (CO2) emissions from cars. See Emissions of Greenhouse Gases in the U.S. for the latest reports on carbon dioxide emissions and its impact on global warming. Almost all motor vehicles today burn some kind of "hydrocarbon" fuel be it gasoline, diesel fuel, propane or alcohol. A hydrocarbon is any substance that contains hydrogen and carbon. This includes crude oil, gasoline, diesel fuel, natural gas, coal, wood and even you and me. In other words, hydrocarbons are the chemical building blocks of all living matter past and present. The crude oil we pump from underground today came from ancient peat bogs and forests from millions of years ago - or so the theory goes.
THE CARBON CYCLE When anything that contains hydrocarbons is burned, the bonds that bind the hydrogen and carbon atoms together are
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broken. This releases heat energy, which can then be put to use to power a motor, heat a boiler, cook a meal or whatever. Burning also causes the hydrogen and carbon atoms to combine with oxygen in the air forming water vapor (H20) and carbon dioxide (CO2). That's the basic chemistry of all combustion. Water vapor is no problem because two-thirds of the Earth's surface is covered with it. So what's a little more? The problem is carbon dioxide. CO2 is a colorless, odorless, nontoxic, harmless gas. Human beings and animals exhale carbon dioxide with every breath they take. Add to this all the CO2 that's being produced by every motor vehicle that's being driven, by every furnace that's burning some type of fuel, by every flame that's burning anywhere in the entire world and it adds up to zillions of tons of CO2. Were it not for plants, we all would have suffocated in our own CO2 a long time ago. Fortunately, plants have the ability to absorb CO2 from the atmosphere and convert it back into organic carbon compounds (hydrocarbons) that become part of the plant. The process requires sunlight and is called "photosynthesis." At the same time, plants release oxygen back into the atmosphere, which we can then use to breathe and burn up more hydrocarbons. Back to CO2. Historically, the amount of naturally occurring CO2 in the atmosphere has been 290 parts per million (only 0.0003%). Air is mostly nitrogen (78%) and oxygen (21%). CO2 is not a pollutant in the traditional sense, but it does retain heat in the Earth's atmosphere. That's why scientists refer to CO2 as a "greenhouse gas." It traps and holds heat just like the glass in a greenhouse. Based on analysis of air bubbles trapped in ice cores taken at the north and south poles, scientists say the level of CO2 has been gradually rising since the dawn of the Industrial Revolution in the 1700s. When people started burning wood and coal to fuel industrial steam engines and heat their homes, CO2 levels started to rise and have been going up ever since. And since World War II, the rate of increase has been accelerating at an ever quickening pace. The latest count puts CO2 at over 360 parts per million (about a 25% increase). As CO2 levels continue to rise, scientists fear it will cause a gradual warming of the Earth's average temperature -- which they say has already gone up almost a couple of degrees based on historical data. This, they say, has the potential to upset ocean currents, global weather patterns and rainfall -- which may have far reaching and negative consequences for agriculture, fishing and life in general. Some fear it may even lead to a melting of the polar ice caps causing the oceans to rise and flood coastal areas. In Al Gore's documentary, "An Inconvenient Truth", he quotes a lot of scary statistics about what's happening with the earth's climate as a result of rising levels of CO2 in the atmosphere. I would highly recommend seeing this movie, whether you think rising levels of CO2 in the atmosphere is causing climate change or not.
KYOTO PROTOCOL Concerns over such dire predictions lead to a world summit meeting in Kyoto, Japan in December, 1997. The outcome of this meeting was a proclamation calling for significant reductions in CO2 emissions by industrialized nations as well as developing nations. The Kyoto Protocol, as it was called, has yet to be finalized. Though many others nations have signed it (including most of the Europeans), the U.S. has balked at signing it because it would call for drastic changes in the American lifestyle. To reduce CO2 emissions from cars, we would have to drive smaller, more fuel efficient cars, raise the fuel economy requirements for trucks, and adopt a variety of conservation measures to reduce energy consumption. Given the current political climate and economic slowdown, it seems highly unlikely the Bush administration will ever sign the Kyoto Protocol.
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SUVS VERSUS TREES If cars and trucks put carbon dioxide into the atmosphere and trees remove it, how many trees does it take to offset the carbon released by one sport utility vehicle? The following calculations may be subject to debate, but here are my ballpark guesstimates: One gallon of gasoline weighs about 6.2 lbs. Of that, over 5 lbs. is carbon (the rest is hydrogen). According to the EPA, burning one gallon of gasoline produces about 19.4 pounds of carbon dioxide (CO2). If a SUV that gets 15 mpg is driven 15,000 miles a year, it will burn 1,000 gallons of gas. That puts about 19,400 lbs. of carbon into the atmosphere (combined with oxygen as CO2). A mature tree 40 to 50 feet high weighs around 10,000 lbs. Of that, at least 7,000 lbs. is organic carbon compounds (the exact amount will vary depending on the species and the density of the wood). To reach this size, most trees need 30 to 40 years of growing time. This too will vary depending on the species of tree, its geographical location, soil conditions and weather. Trees in hot, wet tropical climates grow a lot faster than trees in northern climates. Assuming these estimates are reasonably accurate, one to two mature trees contains about as much carbon as the gasoline burned by a typical SUV in a year.
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But remember it takes 30 to 40 years for the tree to absorb all that carbon from the atmosphere. The process of "photosynthesis" takes time. Leaves use sunlight and water to convert CO2 from the atmosphere into sugar that the tree uses to grow and build more wood fiber. The tree's average carbon uptake, therefore, may only be about 200 lbs. of carbon a year. To offset the carbon released by driving a SUV 15,000 miles a year, therefore, it takes at least 35 medium-sized healthy trees to convert CO2 into wood. What happens to the carbon once it's been taken out of the atmosphere by the trees and bound up in the wood? It stays there until something happens to the tree. If a tree dies of old age or is blown down in a storm, the wood eventually rots. Some of the carbon is slowly released back into the atmosphere as CO2 while the wood rots, but this may take several years. Much of the carbon remains in the soil as organic nutrient for other plants, worms and insects. If the tree is cut down and made into lumber, the carbon also stays bound up in the lumber until something happens to whatever the lumber was used to build. But if the tree is destroyed in a forest fire, is burned to clear land or is cut for firewood, all of the carbon that's been stored in the tree since it was a sapling is immediately released back into the atmosphere as CO2. Consequently, burning a tree is the carbon equivalent of driving a gas-guzzling SUV for a year. Here's another fact to ponder. Every time a farmer in a Third World country clears and burns an acre of heavily wooded forest to grow sweet potatoes or graze cattle (a practice called "slash and burn" agriculture), he releases as much carbon into the atmosphere as 400 SUVs do in a year! And many of these farmers will slash and burn 20 to 50 acres a year. In Brazil alone, nearly 3 million acres of rain forest are being slashed and burned into oblivion every year. Multiply these acres times the amount of carbon that's being put back into the atmosphere and it far outweighs the CO2 that's being released by the entire U.S vehicle fleet! The point here is that no matter what we do to minimize pollution or improve fuel economy will make much difference in restoring the atmospheric carbon balance if deforestation continues to run rampant in other parts of the world. The losses there will more than offset any gains we might be able to achieve here.
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What's really sad about all of this is that forest land cleared by slash and burn agriculture is only productive for a few years because the soil is thin and poor. It soon becomes rock hard forcing the farmers to clear even more land. To make matters worse, the cleared land doesn't come back. The trees are gone forever along with their ability to absorb carbon from the atmosphere. And without the trees, there's not much hope of restoring a natural atmospheric carbon balance.
FUTURE CONSEQUENCES OF CO2 EMISSIONS? We now have more motor vehicles than we do licensed drivers in this country (210 million). The worldwide vehicle fleet is estimated to be about 430 million cars and trucks (up from 50 million in 1950), and will surpass 650 million within the next 8 to 10 years! Most of this growth is occurring in developing nations that do not have the strict emission requirements that we do. And even if they do adopt the same emission standards as Europe, Japan and the U.S., all of these vehicles will still produce millions of tons of CO2 as a byproduct of burning gasoline and diesel fuel. With fewer trees left to absorb carbon and more vehicles producing carbon, don't expect the atmosphere's carbon balance to improve any time soon. The scales have probably tipped irreversibly toward higher and higher levels of CO2 for the foreseeable future. Some scientists say 350 parts per million (ppm) is the maximum amount of CO2 in the atmosphere we can tolerate without adverse climate changes. We are currently at 392 ppm. The biggest unknown is what effect all of this will eventually have on all of us. Nobody argues with the fact that the amount of CO2 in the atmosphere is steadily rising because of human activity. What we don't know is what the long term consequences of a CO2 imbalance will be or how it will actually affect our daily lives. Waiting to find out may prove costly if we miss the window of opportunity to make significant changes now. Many environmentalists say one step we can take now to reduce CO2 emissions is to improve the fuel economy of all classes of vehicles. U.S. fuel economy standards have nearly doubled since the energy crisis days of 1973 -- but have remained relatively flat at 27.5 mpg for passenger cars for the last 15 years. For trucks, the average fuel economy is only about 20 mpg. Yet because of the increased popularity of trucks and SUVs in recent years, the average fuel economy of all new vehicles in the U.S. has sunk to the lowest level since 1980! According to the Sierra Club, every day America consumes 18 million barrels of oil. Not all of that is for transportation, but in a year's time we burn up about 120 billion gallons of gasoline. If the Corporate Average Fuel Economy (CAFE) standards for trucks were raised to match that of cars (27.5 mpg), it could save one million barrels of oil per day. That's a lot of carbon! Raising the CAFE standards for cars and light trucks could save millions of barrels of oil per day.
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Rising fuel prices rather than Congressional action (or inaction as the case may be) will likely provide the strongest incentive to get motorists to buy more fuelefficient vehicles and reduce their driving. But it's hard to cut back on the number of miles driven (we drive over two trillion miles a year now) because our cities and suburbs are sprawled out across the land. Most people are totally dependent on a motor vehicle to get to work, school, to shop and do everything else in life (thankfully for those of us in the parts and service business). Mass transit doesn't work outside the central cities because things are too spread out. And in rural America, a car or a truck is the only way to get to town or any place else. Calculate Your Carbon footprint If you want to calculate how much carbon you and your lifestyle are putting into the atmosphere, Click Here for the American Council on Renewable Energy Carbon Footprint Calculator. TECHNOLOGY TO THE RESCUE One solution that can allow us to keep our big SUVs and get good fuel economy too is "hybrid-electric" technology. With this approach, a small displacement, fuel-efficient gasoline or diesel engine is used in conjunction with an electric motor and battery to power the vehicle. The regular motor is used for highway driving and to charge the battery. The rest of the time the vehicle runs on electric power or a combination of battery and gasoline. Depending on how the control strategy is set up, a hybrid-electric may deliver double the fuel economy of a conventional vehicle in normal driving, and even triple the usual mileage in urban stop-and-go driving. Instead of wasting fuel at a stop light, a hybrid-electric shuts the engine off when the vehicle stops. The engine remains off until the light changes and the vehicle accelerates on battery power up to a certain speed. As promising as this new technology is, only a few vehicle manufacturers are producing hybrid-electric vehicles: Toyota, Honda, Ford and GM. The Toyota Prius is a compact four-door car that has an EPA rating of 52 mpg in the city and 45 mpg on the highway. But production is limited due to limited battery manufacturing capacity. It's the same story for most of the other hybrid vehicles that are currently available. They are limited in number and hard to find. Electric vehicles are still on the fringe and will probably stay there because of lagging battery technology. Electric vehicles that emit no pollutants and no CO2 certainly make sense in polluted urban environments. They're the ultimate energy-efficient vehicle for stop-and-go driving because they waste no energy when they're stopped in traffic. But nobody has yet come up with a cheap, lightweight, safe, quickly rechargeable battery. And even if they did, it would take years for the new technology to go into mass production and for the public to accept it. There's also the issue of whether or not electric vehicles would actually reduce pollution. The electricity needed to recharge the battery has to come from another power source. Unless that power source is nuclear, hydroelectric, wind, solar or geothermal, there is little or no net reduction in pollution or CO2 because most electrical power in this country is generated by burning coal or natural gas. No new nuclear power plants have been built in the U.S. for over 25 years, and many nukes are now reaching retirement age and will have to be decommissioned. Unless there is a rebirth of nuclear energy or a large scale shift to alternative sources of clean power (which are more expensive and require huge financial investments), electric vehicles aren't going far. Even with an advanced battery breakthrough, some question whether the existing power infrastructure has enough capacity to supply the needs of an expanding fleet of electrical vehicles. Several years ago, California suffered rolling blackouts which were supposedly due to an energy shortage. The shortage turned out to be a hoax perpetrated by the electric companies to drive up their prices and profits. Today, some experts say the U.S. has enough excess electric generating capacity to power up to 80% of all the vehicles on the road if they were electric or electric-hybrid vehicles. The oil companies obviously wouldn't like that to happen, and are doing everything they can to downplay the potential of electric vehicles. Anyone who thinks otherwise should watch the documentary Who Killed The Electric Car?
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FUEL CELLS & HYDROGEN Hydrogen Fuel cells currently hold the greatest promise for solving our environmental concerns over pollution and CO2. A fuel cell produces electricity by combining hydrogen and oxygen. The only byproduct is water vapor -- provided the fuel source is pure hydrogen. Hydrogen is one of the most abundant elements on Earth. It can be made from natural gas, oil or even coal, or by using electricity to break down water into hydrogen and oxygen. Even so, it is expensive to produce and contains much less energy per liter than other hydrocarbon fuels. Hydrogen is also a hard-to-store fuel. Because hydrogen is a gas, it has to be compressed at extremely high pressure (3,000 to 4,800 psi). This requires large, heavy, expensive fuel tanks that reduce a vehicle's driving range and fuel economy. It can be liquefied to increase its storage density, but this requires special insulated cryogenic storage tanks to keep the fuel at -253 degrees C. Another storage method is to use "metal hydrides" or activated carbon that absorb hydrogen like a sponge. But these approaches are also bulky, heavy and expensive. What's more there is no distribution system for hydrogen like there is for gasoline, diesel fuel or even natural gas. So even if you had a hydrogen powered vehicle today, you would have a very difficult time finding a place to fill it up. One solution for storing hydrogen is to not store it as a gas but to extract it from another fuel such as gasoline or methanol alcohol. A device known as a "reformer" can break down these fuels to release the hydrogen. But adding a reformer adds cost and complexity, and also reduces its fuel efficiency. A reformer also does nothing to reduce our dependence on oil. Even so, Chrysler, Mercedes. BMW and several other vehicle manufacturers have all demonstrated prototype fuel cell powered vehicles that use reformers to extract hydrogen from gasoline or methanol. Why not just burn hydrogen in an internal combustion engine and forget the high tech fuel cell and reformer? You can, but compared to other fuels hydrogen is a lousy motor fuel. It has a very low octane number, which means it causes detonation and preignition unless the compression ratio is cut way down. It also tends to backfire through the intake manifold. And it doesn't get very good fuel mileage, either. A gallon of liquefied hydrogen has only about one fourth the energy content of a gallon of gasoline. Time will tell which technologies will eventually help us meet our environmental challenges. It's not just motor vehicles that bear the brunt of reducing pollution and CO2 emissions. It's all forms of energy consumption and power generation worldwide as well as the issue of deforestation. Hopefully, we can come up with solutions that satisfy everybody's concerns and needs while there is still time. Update: December 2006
Burning Palm Oil No Solution Either In recent years, some power generating plants in Europe have been using palm oil as a substitute for petroleum because palm oil is a renewable biofuel that is carbon neutral, and it is relatively cheap. But a new report issued in late 2006 by Wetlands International, Delft Hydraulics and the Alterra Research Center of Wageningen University in Holland found that burning palm oil isn't such a great idea after all. The study measured the carbon released from peat swamps in Indonesia and Malaysia that had been drained and burned to plant palm oil trees. About 85 percent of the world's palm oil comes from the two countries, and about one-quarter of Indonesia's plantations are on drained peat bogs. The four-year study found that 600 million tons of carbon dioxide seep into the air each year from the drained swamps. Another 1.4 billion tons go up in smoke from fires lit to clear rain forest for plantations, smoke that often shrouds Singapore
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and Malaysia in an impenetrable haze for weeks at a time. Together, those 2 billion tons of CO2 account for 8 percent of the world's fossil fuel emissions, the report said. Draining the peat swamps to grow palm trees has had a very negative impact. Not only has it increased carbon emissions significantly, but it has also destroyed wetland ecosystem that can take carbon out of the atmosphere. Update: November 29, 2007:
New Report Says U.S. Can Reduce Greenhouse Gas Emissions Significantly Without Significant Pain A new report called Reducing US Greenhouse Gas Emissions: How Much at What Cost? published jointly by McKinsey & Company (a management consulting firm) and The Conference Board (a business research organization) says the United States could reduce projected 2030 emissions of greenhouse gases by one-third to one-half at manageable costs to the economy and without requiring big changes in consumer lifestyles. The report is based on detailed analysis of 250 opportunities for reducing emissions of carbon dioxide and other gases thought to contribute to global warming. If no changes are made, annual U.S. greenhouse gas emissions will increase by 35 percent to reach 9.7 gigatons of carbon dioxide equivalent (CO2) in 2030, according to an analysis of government forecasts. At this level, emissions would overshoot by 3.5 to 5.2 gigatons the targets implied by economy-wide climate change bills introduced in Congress. A gigaton is one billion metric tons. The report shows a reduction of 3.0 to 4.5 gigatons in 2030 is achievable at manageable cost using proven and emerging high-potential technologies, but only if the U.S. pursues a wide array of options and moves quickly to capture gains from energy efficiency. Almost 40 percent of the greenhouse gas emission reductions identified come from options that more than pay for themselves over their lifetimes, thereby creating net savings for the economy. For example, improving energy efficiency in buildings, appliances and industry could yield net savings while offsetting some 85 percent of the projected incremental demand for electricity in 2030. However, the report warns that private sector innovation and policy support will be necessary to unlock these and other opportunities. The report analysis focused on options likely to yield greenhouse gas reductions at a cost of less than $50 per ton of CO2 equivalent (CO2e). Among the main findings: * Opportunities to reduce greenhouse gas emissions are highly fragmented and widely spread across the economy. The largest single option, carbon capture and storage (CCS) for coal-fired power plants, offers less than 11 percent of total potential identified. The largest sector, power generation, accounts for less than one third of the total. * Reducing emissions by 3 gigatons of CO2e in 2030 would require $1.1 trillion of additional capital spending, or roughly 1.5 percent of the $77 trillion in real investment the U.S. economy is expected to make over this period. * Investment would need to be higher in the early years, in order to capture energy efficiency gains at lowest overall costs and accelerate the development of key technologies, and would be highly concentrated in the power and transportation sectors. * If pursued, such investment would likely put upward pressure on electricity prices and vehicle costs. Policymakers would need to weigh these added costs against the energy efficiency savings, opportunities for technological advances, and other societal benefits. * Five clusters of initiatives, pursued in unison, could create substantial progress towards the targets implied by bills currently before Congress. From least to highest average cost, they are: Improving energy efficiency in buildings and appliances (710 to 870 megatons); Increasing fuel efficiency in vehicles and reducing carbon intensity of transportation fuels (340 to 660 megatons); Pursing various options across energy-intensive portions of the industrial sector (620 to 770 megatons); Expanding and enhancing carbon sinks, such as forests (440 to 590 megatons); Reducing the carbon intensity of electric power production (800 to 1,570 megatons.) The report was produced in association with DTE Energy, Environmental Defense, Honeywell, National Grid, Natural Resources Defense Council, PG&E and Shell. Update: Dec 20, 2007
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EPA REJECTS CALIFORNIA GREENHOUSE GAS REGULATIONS The U.S. Environmental Protection Agency has denied California's waiver request to regulate carbon dioxide (CO2) emissions from automobiles starting in 2009. The CO2 rules were issued by the California Air Resources Board and adopted by 12 other states. The EPA overturned the regulations on the same day that President Bush signed into law an energy bill to raise the Corporate Average Fuel Economy (CAFE) Standards for passenger cars and light trucks by 40% to an industry average of 35 miles per gallon by 2020. SEMA worked with the automakers and other industry associations as part of the CAFE Coalition to help negotiate a compromise to the new fuel economy standard. Under the new federal law, the amount of renewable fuel used will increase to at least 36 billion gallons. According to the EPA, the new CAFE law and renewable fuel provisions will achieve greater greenhouse gas savings than the California program. Additionally, the federal approach provides a national solution, as opposed to a potential patchwork of state rules. Under the Clean Air Act, California may seek a waiver to establish its own air quality rules (which can then be adopted by other states). This is the first time the EPA has completely rejected a waiver request. The agency noted that previous waiver petitions covered pollutants that predominantly impacted local and regional air quality. The EPA reasoned that a national framework for addressing greenhouse gases is necessary since the emissions are global in nature and impact every state. California intends to appeal the EPA decision. Additionally, the Supreme Court recently directed the EPA to study the problem of greenhouse gases, paving a path to for EPA to potentially recommend even more stringent regulations if, in consultation with the National Highway Traffic Safety Administration, it deems them necessary. More to come . . . . . . Update: June 2010
Obama Administration Announces New Fuel Economy Rules for Auto Makers In April, the Obama administration said auto makers will have to increase their Corporate Average Fuel Economy (CAFE) numbers significantly over the next six years. The new rule sets a goal of 35.5 mpg by 2016, and a fleet average of 54.5 miles per gallon by 2025. This will lower greenhouse gas (GHG) emissions produced by the average vehicle to 250 grams per mile. Achieving this goal will require roughly a 5 percent increase in fuel efficiency each year, starting in model year 2012. The gains will be achieved by switching to smaller displacement, more fuel efficient engines (many of which will use direct gasoline injection and turbocharging), and reducing vehicle weight by downsizing and using lighter weight materials.
Update: July 2012
Global Warming Skeptic Finally Admits It Is True! Physics professor Richard A. Muller of the University of California-Berkeley says he is no longer a skeptic of Global Warming. His investigation of climate data proves that human activity is increasing the release of carbon dioxide, and that CO2 is causing a gradual rise in average temperatures worldwide. Furthermore, he says Global Warming is likely to accelerate in the coming years. Muller has long been an outspoken critic of Global Warming, saying that some studies were flawed or that the data was not very accurate. After undertaking an exhaustive study of his own (the Berkeley Earth Surface Temperature Project), he is now singing a different tune. Three years of research confirmed everything other scientists have been saying about global Warming. Yes, it is real and yes Global Warming is mostly due to human activity. Muller says he is worried about the ultimate consequences of Global Warming, and how far it will go and how fast it will proceed. The long term outlook is not good, he says.
Update: November 2012
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How Carbon Dioxide Emissions from Cars Affect the Environment
Atmospheric CO2 Levels Hit All-Time High Carbon dioxide levels reached 390.9 parts per million last year, according to a new report from the World Meteorological Organization (WMO). The new level is 140 percent higher than the pre-industrial level of 280 parts per million and nearly 2 parts per million higher than the 2010 carbon dioxide level. The WMO estimates that about 413 billion tons (375 billion metric tons) of carbon have been released into the atmosphere since 1750, primarily from fossil fuel combustion. About half of this atmospheric carbon dioxide remains in the atmosphere, and much of it will linger for centuries, causing the planet to warm further warns the WMO. To read the WMO report (release #965), Click Here.
To read more dire predictions of what will happen if CO2 emissions are not reduced, see Report Warns Mankind Approaching Carbon Cliff.
Update: May 3, 2013
Atmospheric CO2 to Hit Highest Level in 3-Million Years! According to the latest data from the Mauna Loa Observatory in Hawaii, where atmopsheric levels of carbon dioxide (CO2) have been monitored daily since 1958, CO2 levels are set to surpass 400 parts per million (ppm) this spring. This is the highest recorded level of CO2 since the Pliocene Epoch 3 to 5 million years ago. At that time, the planet was much warmer and wetter averaging 5.4 to 7.2 degrees F than today with sea levels as much as 131 feet higher than today. The "Keeling Curve" is a graph that shows how quickly CO2 levels are rising. The curve shows that CO2 has been rising at a faster and faster rate every year. Back in 1958 when they first started measuring CO2 levels, the average concentration was around 313 ppm. The actual level of CO2 varies by season, rising through May and then dropping until it reaches a seasonal minimum in October. The rising and falling levels result from the growth of trees and vegetation that absorb CO2 from the atmosphere during the growing season, and release it in the winter. Prior to the Industrial Revolution (late 1700s to early 1800s), atmospheric CO2 levels has been relatively constant, averaging around 270 to 280 ppm. But as the world became more and more industrialized and the use of fossil fuels exploded, so has the release of CO2 from human endeavors. In the 1950s and 1960s, the rate of increase in CO2 was slightly less than 1 ppm. But in the past 50 years, it has skyrocketed to 2 to 2.5 ppm per year. Though the U.S. and many European countries are trying to reduce CO2 emissions by requiring more fuel efficient vehicles and lighting, and shifting more power generation to wind mills, China and India are more than offsetting any gains in other parts of the world by rapidly expanding their use of coal for power generation. China and India have both announced plans to build hundreds of new coal fired power plants to feed their growing economies. Given the current trends, it seems unlikely we can reverse this CO2 trend any time soon (if ever!). Currently, China accounts for nearly one fourth of all carbon dioxide emissions worldwide, releasing 10 billion tons a year into the atmosphere. To make matters worse, China's CO2 emissions are increasing about 10 percent a year. By comparison, the U.S. (which is the 2nd largest producer of CO2) has reduced its CO2 emissions to 5.9 billion tons per year (mostly by outsourcing manufacturing jobs to China).
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Automotive Environmental Impact
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Automotive Environmental Impact Copyright AA1Car 2012 Cars are a great means of personal transportation, but they have created a variety of environmental concerns. Here's a list of some of the environmental impacts automobiles are having today:
Carbon Dioxide (CO2) The biggest environmental issue today with respect to cars is their impact on global warming from carbon dioxide emissions in the exhaust. Catalytic converters have greatly reduced most of the other major pollutants in automotive exhaust (unburned hydrocarbons, carbon monoxide and oxides of nitrogen), but converters don't reduce the amount of CO2 because CO2 is a natural byproduct of combustion. In fact, you produce CO2 anytime a fossil fuel that contains carbon is burned. An electric vehicle powered by a hydrogen fuel cell won't produce any CO2, but that technology is a long ways off from mass production. http://www.aa1car.com/library/automotive_environmental_issues.htm
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Plug-in electric vehicles look like the better solution, provided the electricity is produced by a green source such as wind, geothermal, hydroelectric or solar cells. Electricity from a nuclear power plant is also green as far as CO2 emissions are concerned (there are none), but there's the issue of radioactive waste disposal and possible leakage.
A/C Refrigerants Back in the mid-1990s, R134a refrigerant replaced R12 to address the ozone depletion issue caused by man-made CFC refrigerants. R134a contains on chlorine, so that apparently solves that issue. But R134a is a greenhouse gas that can contribute to global warming. The refrigerant causes no problems as long as it remains sealed inside the A/C system. But if it escapes into the atmosphere either as a result of leaks, an accident or intentional venting, it does contribute to the global warming problem. It's not much, but every little bit adds up over time. So to address this issue, automakers are looking to replace R134a with either HFO 1234yf or carbon dioxide (CO2). R134a has a Global Warming Potential (GWP) of 1400 versus 4 for HFO 1234yf versus 1 for CO2. The drawback with CO2 is that is requires a totally revamped high pressure A/C system and all new service equipment. Transitioning to HFO 1234yf is seen as the more practical alternative. Read he following article for more information about Alternative Refrigerants
Lead Lead is a toxic heavy metal that can cause a variety of environmental ills. Tetraethyl lead was once used as an octaneboosting additive in gasoline. But studies found that lead from automotive exhaust fumes was causing lead pollution in many urban areas, so lead fuel additives were phased out in the early 1970s. Lead still remains in car batteries, but is not an environmental concern because 98% of car batteries are recycled. The latest lead issue is with wheel balance weights. California and a growing number of other states want to ban lead tire weights because the weights sometimes fall off, decompose and allow lead dust to find its way into lakes and streams . Personally, I think this is a stretch and don't think this poses any significant environmental danger. Even so, the tire service industry is starting to move away from lead weights to more benign materials such as steel and zinc (though zinc has some environmental issues, too). Read the following article for more information about wheel balance weights: Wheel Balancing
Copper in brake linings Small amounts of copper (less than 10 percent) are used in many brake linings to help dissipate heat. But as the brake pads wear, it creates dust that contains particles of copper. Scientists say copper in brake dust is an environmental contaminant that is harmful to aquatic organisms so efforts are being made to require friction manufacturers to reduce or eliminate the amount of copper in brake pads. California and Washington have already passed laws that will phase out most of the copper in brake linings by 2021. Other states are considering similar legislation.
Asbestos This was once considered to be a great friction material for brakes, clutch linings and gaskets. But because of the health risks associated with exposure to asbestos dust (mesothelioma lung disease), asbestos was mostly phased out of brakes back in the 1980s. Asbestos did not present any serious health risk to motorists, but it did to people involved in asbestosrelated manufacturing and mining, and also to automotive service technicians who worked on brakes. Today, asbestos is mostly history but it can still be found in some aftermarket replacement brake linings that are made outside the US but imported into the US market. Because of this, brake dust can still be a potential health hazard. Read the following articles for more information about Asbestos and Brake Dust
Toxic chemicals in interior plastics and fabrics Car makers use a wide variety of plastics and upholstery materials in vehicles. Many people like that "new car smell," but the fumes that create the odor often contains volatile organic compounds and other chemicals that outgas from the plastics. Many of these fumes are toxic or carcinogenic and may increase a motorist's health risk over time. Scientists disagree on what level of exposure is too high, but many say it's not a good idea to breathe these fumes if they can be avoided. Some advise rolling down the windows and allowing the fumes to vent out before driving a car has been parked in the hot sun all day. Auto makers are making more effort to reduce the use of plastics and materials that give off potentially toxic fumes. But many vehicles still generate levels of toxic fumes that some say are too high.
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Read the following article for more information on Toxic Chemicals In Your Car's Interior
Used Motor Oil Used motor oil can contaminate ground water if it is disposed of improperly by someone who changes their own oil. Fortunately, most of the motor oil that's changed annually is recycled properly either by service outlets or by DIYers who bring their used motor oil to an auto parts store or other facility that accepts used motor oil for recycling. Several oil companies are now marketing recycled oil as a green alternative to conventional motor oil.
Used Antifreeze Like motor oil disposal is the main issue here. Ethylene glycol can be toxic to plants and animals, but it does gradually break down over time if it finds its way into a river or lake. It can be disposed of by pouring it into a toilet, but should never be disposed of by dumping it on the ground or down a storm sewer. Coolant can be recycled, and many auto service facilities now use coolant recycling machines that clean and rejuvenate the coolant in a vehicle's cooling system. Read the following article for more information about Coolant Recycling
Used Tires The issue here is tire disposal. A set of tires will typically last 60,000 to 80,000 miles or more. But eventually, the tread wears out and the tires have to be replaced. Most tire stores charge a tire disposal fee that covers their cost of sending the tires to an approved tire disposal site or facility. Old tires can be shredded and recycled into paving asphalt, or they can be burned (under controlled conditions only to minimize pollution), or cooked down to recover their valuable hydrocarbons and other ingredients. But mostly, they are simply stockpiled in huge piles that create breeding grounds for mosquitoes and environmental eyesores. If a pile of old tires catches fire, it can burn for days creating thick black clouds of acrid smoke.
Junk Cars Most of the metal in a vehicle (steel, aluminum & copper) is usually recovered for recycling after a vehicle has been scrapped. Many good usable parts such as fenders, hoods, doors, windshields, etc. are removed from junk cars to find a second life as a replacement part to fix another vehicle. Other parts such as engines, transmissions, alternators and starters are recovered and rebuilt to be sold in auto parts stores. This saves considerable energy and environmental impact compared to mining and processing virgin iron and aluminum and making new parts from scratch.
Plastics Though many plastics are recyclable, most of plastics in scrapped automobiles ends up as ground up fluff that goes into a landfill. More work is being done to identify and recycle plastics at a vehicle's end of life, and auto makers are using more recycled plastics in new parts as well. But we still have a long ways to go to to reduce the environmental impact of plastics in junked vehicles.
Drilling, Refining & Pipelines A growing demand for oil from which gasoline is made is fueling a demand for more offshore drilling, more extraction of oil from oil shale and sand, and more pipelines to carry crude oil to refineries. All of these have their own associated environmental impacts and risks. As the world's car population grows, especially in China, the world's oil supply may not be able to keep up, increasing the potential for future military conflicts.
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Emissions Testing: Will Your Car Pass?
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Emissions Testing: Will Your Car Pass? Fixing Emissions Test Failures Copyright AA1Car Adapted from an article written by Larry Carley for Tire Review magazine
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. Emissions testing or Smog testing is used in many areas of the country to improve air quality. But even if your community is not affected, you still need to know about emissions testing and smog checks because problems that often cause emission failures can also cause a variety of driveability and performance complaints. Mandatory emissions testing has become a fact of life in many areas as a means of identifying vehicles that are "gross polluters" so they can be fixed. See Vehicle Emissions I/M Programs to see if your state requires emissions testing. Such programs force vehicle owners to have emission problems repaired that might otherwise be ignored. So when a vehicle fails an emissions test or a smog check, most motorists are not exactly overjoyed to learn that repairs are needed. Everybody is for clean air as long as somebody else pays for it. That is why all new cars and light trucks built from 1981 through 1995 have had a 5 year, 50,000 mile federal emissions warranty. This warranty covered all emission control components as well as the fuel delivery system (except the pump and filter), ignition system (except spark plugs), and engine management system including all sensors. In 1995, the federal emissions warranty requirements changed. The warranty was extended to 8 years and 80,000 miles on the powertrain control module and catalytic converter, but rolled back to only 2 years and 24,000 miles on everything else. Even so, all of these components are still covered for 3 years or 36,000 miles (or longer) by the individual vehicle manufacturers bumper-to-bumper warranties. In California, the coverage is much longer. Once a vehicle is out of warranty, the burden of paying for emission repairs becomes the sole responsibility of the vehicle owner. Most inspection programs include "waiver" provisions that limit the amount of money motorists have to spend on emission repairs. If an emissions problem cannot be resolved within the specified waiver limit (which may be anywhere from $50 up to $450 depending on the local regulations and applicable model year), the vehicle gets a "pass" even though it may still be a polluter. The objective, therefore, is to get the most bang for your repair buck (the most pollution reduction for the least out-of-pocket repair expense). When a vehicle has multiple problems (one or more fouled or worn spark plugs, one or more bad plug wires, plus worn rings and valve guides), zero in on the repairs that will make the most noticeable improvement. A single misfiring plug, for example, can increase hydrocarbon emissions enormously (10 times normal!). Replacing the spark plugs (and plug wires if
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necessary) will eliminate the misfire problem (at least temporarily) and make a dramatic difference in reducing the engines overall emissions. The vehicle may still not be in compliance because the engine is burning oil, but it will run cleaner than it did before and have cost far less than an engine overhaul. EMISSIONS TESTING: WHAT IS INVOLVED
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Each state or municipality determines its own cut points for emissions testing as well as the specific tests that must be performed. Most test programs look at only two pollutants: unburned hydrocarbons (HC) and carbon monoxide (CO). Most also measure carbon dioxide (CO2) but only for diagnostic purposes since CO2 is not a pollutant (though it is a "greenhouse gas" that may contribute to global warming). Some inspection programs also require visual checks of various emissionsrelated equipment for evidence of tampering. These include:
Checking the restrictor in the fuel tank filler neck to make sure it has not been knocked out or enlarged to accept regular leaded gasoline. Inspecting the gas cap to make sure it is the correct type for the Professional Export application and seals tight. Services Provided Looking under the car to see that the catalytic converter is in place. Checking the instrument panel to see if the "Check Engine" or Learn More malfunction indicator lamp is illuminated. Checking under the hood to make sure the engine has all the required emission control components (California primarily). Checking any nonstock aftermarket parts on the engine to make sure they are emissions certified (California primarily). If an engine has been swapped or replaced, making sure it has all the required emissions equipment for the original model year and application (California primarily). In areas that have adopted the new I/M 240 test program, checking oxides of nitrogen (NOX) emissions, as well as total emissions in grams per mile as the vehicle is run at various speeds and loads on a dyno. I/M 240 programs may also require checking the integrity of the fuel system for air leaks (evaporative emissions) and the flow capacity of charcoal canister purge valve.
EMISSIONS TEST STANDARDS The cut points for acceptable HC and CO levels are generally based on the emission standards that a vehicle was required to meet when it was new, so older vehicles have more lenient emission standards than new ones (see chart).
EMISSIONS CUT POINT CHART Model year...Typical Cut Points...Well-tuned engine ..............CO%.....HC ppm..........CO%.....HC ppm pre-1968..... 7.5-12.5... 750-2000..... 2.0-3.0... 250-500 1969-70..... 7.0-11.0... 650-1250..... 1.5-2.5... 200-300 1971-74..... 5.0-9.0... 425-1200..... 1.0-1.5... 100-200 1975-79..... 3.0-6.5... 300-650..... 0.5-1.0... 50-100 1980........ 1.5-3.5... 275-600..... 0.3-1.0... 50-100 1981-93..... 1.0-2.5... 200-300..... 0.0-0.5... 10-50 1994 & up..... 1.0-1.5... 50-100..... 0.0-0.2... 02-20 Notice in the emissions cut point chart that the actual emissions produced by the average well-tuned engine are http://www.aa1car.com/library/tr1196.htm
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substantially less than the cut points required to pass an emissions test. The actual cut points are more lenient because the goal of emissions testing is to identify the gross polluters so they can be fixed and brought back into compliance. FAILING AN EMISSIONS TEST When a vehicle fails an emissions test, the motorist usually receives a printout that show the test results of the vehicles emissions as well as the applicable cut points. From this, you can determine if too much HC and/or CO caused the vehicle to fail. Hydrocarbon failures mean unburned gasoline is passing through the engine and entering the exhaust. The three most common causes include ignition misfire, lean misfire and low compression (typically a burned exhaust valve). Ignition misfire can be caused by worn or fouled spark plugs, bad plug wires or a weak coil. Lean misfire results where there is too much air and not enough fuel, so check for vacuum leaks, dirty injectors or a fuel delivery problem. In addition to these, hydrocarbon failures can also be caused by oil burning due to worn valve guides, valve guide seals and/or rings. Carbon monoxide failures indicate an overly rich fuel mixture. On older carbureted engines without electronic feedback controls, look for things like a stuck choke, misadjusted or fuel saturated float or a rich idle mixture adjustment. On newer vehicles with electronic carburetors or fuel injection, the system may not be going into closed loop because of a bad coolant or oxygen sensor. If both HC and CO are high, the vehicle may have a bad catalytic converter or an air pump problem. For more info on catalytic converters, Click Here for Troubleshooting a P0420 Catalyst Code NOX failures are usually EGR-related, since the EGR system is primarily responsible for reducing oxides of nitrogen. But NOX emissions can also be caused by a bad three-way converter or a computer control system that remains in open loop.
EMISSIONS PERFORMANCE CHECKS There are four things you should always check on every vehicle that has a computerized engine control system: 1. Scan for fault codes. Any codes that are found need to be dealt with before anything else. 2. Make sure the system is going into closed loop. No change in loop status often indicates a coolant sensor problem. 3. Confirm that the system is alternating the fuel mixture between rich and lean. This is absolutely essential for the converter to function efficiently. You can do this by observing the O2 sensors output with a scan tool, or directly with a digital storage oscilloscope or voltmeter. If everything is okay, the sensor should be producing an oscillating voltage that flip-flops from near minimum (0.1 to 0.2v) to near maximum (0.8 to 0.9v). O2 sensors in feedback carburetor applications have the slowest flipflop rate (about once per second at 2500 rpm), those in throttle body injection systems are somewhat faster (2 to 3 times per second at 2500 rpm), while multiport injected applications are the fastest (5 to 7 times per second at 2500 rpm). 4. Confirm that the system responds normally to changes in the air/fuel mixture. To test the system response, pull off a vacuum hose to create an air leak (not too large or the engine will die). You should see an immediate voltage drop in the O2 sensor output, and a corresponding increase in injector dwell or mixture control dwell from the computer. Making the fuel mixture artificially rich by injecting some propane into the intake manifold should cause the O2 sensor output to rise and the computer to lean out the fuel mixture.
READING EMISSIONS: EXHAUST GAS ANALYSIS Though a good technician can often diagnose and repair emission problems without having to actually check tailpipe emissions, it is becoming increasingly necessary today to have an infrared exhaust analyzer with at least three gas and preferably four gas (or even five gas) capability. Why? To baseline vehicle emissions for diagnostic purposes, and to verify that the repairs made eliminated or reduced the emissions problem.
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Reading HC and CO at the tailpipe to diagnose emission problems may not give you the complete picture because the catalytic converter "masks" many problems by significantly lowering HC and CO in the exhaust. That is where a three- or four-gas analyzer comes in handy. The relative proportions of carbon dioxide and oxyten in the exhaust can reveal whether the air/fuel ratio is correct or not as well as other problems that affect engine performance and emissions. As combustion efficiency decreases, the oxygen content in the exhaust rises and carbon dioxide falls. An engine that is running at a nearly ideal air/fuel ratio of 14.5:1 will show about 14.5 percent carbon dioxide and 2.5 percent oxygen in the exhaust. Carbon dioxide readings of less than about 13 percent and oxygen readings greater than about 4 or 5 percent indicate poor combustion efficiency. This translates to an over-rich or over-lean air/fuel ratio, poor compression, or an ignition problem.
WHY SOME VEHICLES THAT SHOULD PASS AN EMISSIONS TEST DO NOT Most vehicles that are in good running condition and properly maintained should pass an emissions test. In some cases, though, minor problems may cause the vehicle to fail an emissions test. These include: Engine and/or converter not at operating temperature. If a vehicle is only driven a short distance to the test facility, it may not be warm enough for the engine to be at normal operating temperature and/or the converter at lightoff temperature. This will affect the emissions of the engine and may cause it to fail. Excessive idling while waiting in a test lane may also cause the catalytic converter and/or oxygen sensor to cool down enough where they may not control emissions properly causing higher than normal readings. Idle speed too high. A few hundred rpm can sometimes make the difference between passing and failing an emissions test if emissions are marginal. Dirty air filter. A restricted air filter will choke off the engines air supply, causing higher than normal CO readings. Worn or dirty spark plugs. Excessive plug gap and fouling deposits can create ignition misfire resulting in excessive HC emissions. Dirty oil. The oil in the crankcase can become badly contaminated with gasoline if a vehicle has been subject to a lot of short trip driving, especially during cold weather. These vapors can siphon back through the PCV system and cause elevated CO readings. Pattern failures. Some vehicles tend to be dirtier than others for a given model year because that is the way they were built. It may be the design of the engine, or the calibration of the fuel or engine control system. These kinds of problems may require special "fixes" that can only be found in factory technical service bulletins. In areas that have plug-in OBD II emissions testing for 1996 and newer vehicles, the vehicle will be rejected for testing if all of the required OBD II readiness monitors have not run. This may require driving the vehicle for several days until all the monitors have run. The vehicle will also fail the test if (1) the test computer cannot establish communication with the vehicle PCM (defective or disabled diagnostic connector), (2) if the Malfunction Indicator Lamp (MIL) is on, or there are fault codes in the PCM. If the OBD II system is working properly, the MIL is not on and there are no codes, the vehicle should pass the test.
Does Your State Have an Emissions Inspection Program? Does your state have an emissions inspection and testing program? You can find out by going to the Equipment and Tools Institute website at ETI Emission Testing Program Information by State. Currently, there are 30 states and the District of Columbia that have Inspection/Maintenance programs in the U.S., and there are two programs in Canada. Highlights of those programs, including governing state agency, program descriptions, contact information, test protocols, test frequency and related fees, are shown on the ETI page.
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Basic Emission Control Systems Copyright AA1Car When the first emission controls were first introduced back in the late 1960s, they were primarily "add-on" components that solved a particular emission need. When positive crankcase ventilation (PCV) became standard in 1968, the recycling of crankcase vapors eliminated blowby emissions as a major source of automotive pollution. When Evaporative Emission Control Systems were added in 1971, charcoal canisters and sealed fuel systems eliminated fuel vapors as another factor that contributed to air pollution. Exhaust gas recirculation (EGR) was added in 1973, which lowered harmful oxides of nitrogen (NOX) emissions. But the most significant add-on came in 1975 when the auto makers were required to install catalytic converters on all new cars. The catalytic converter proved to be a real breakthrough in controlling emissions because it reduced both unburned hydrocarbons (HC), a primary factor in the formation of urban smog, and carbon monoxide (CO), the most dangerous pollutant because it can be deadly even in small concentrations. The converter slashed the levels of these two pollutants nearly 90%! The early two-way converters (so-called because they eliminated the two pollutants HC and CO) acted like an afterburner to reburn the pollutants in the exhaust. An air pump or an aspirator system provided the extra oxygen in the exhaust to get the job done. Two-way converters were used up until 1981 when three-way" converters were introduced. Three-way converters also reduced NOX concentrations in the exhaust, but required the addition of a computerized feedback fuel control system to do so. Unlike the earlier two-way converters that could perform their job relatively efficiently with a lean fuel mixture, the catalyst inside a three-way converter that reduces NOX requires a rich fuel mixture. But a rich fuel mixture increases CO levels in the exhaust. So to reduce all three pollutants (HC, CO and NOX), a three-way converter requires a fuel mixture that constantly changes or flip flops back and forth from rich to lean. This, in turn, requires feedback carburetion or electronic fuel injection, plus an oxygen sensor in the exhaust to keep tabs on what is happening with the fuel mixture. Like the earlier two-way converters, three-way converters also require extra oxygen from an air pump or aspirator system, and some "three-way plus oxygen" converters are designed so air is routed right to the converter itself for more efficient
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operation.
CATALYTIC CONVERTER REPLACEMENT Original equipment converters are designed to last up to 150,000 miles or more, which many do provided they are not poisoned by by lead, silicon or phosphorus. When leaded gasoline was still available, fuel switching to save money caused the premature demise of many a converter. Lead coats the catalyst rendering it useless. Silicon, which is used in green formula and hybrid OAT formula antifreeze, and certain types of RTV sealer, has the same effect. Coolant leaks in the combustion chamber can allow silicon to enter the exhaust and ruin the converter. Phosphorus, which is found in motor oil, can foul the converter is the engine is burning oil because of worn valve guides or rings. The latest motor oils have significantly reduced levels of ZDDP (phosphorous) anti-wear additive to reduce the risk of converter contamination. Converters may also fail if they get too hot. This can be caused by unburned fuel in the exhaust. Contributing factors include a rich fuel mixture, ignition misfire (a fouled spark plug or bad plug wire) or a burned exhaust valve that leaks compression. Fuel in the exhaust has the same effect as dumping gasoline on a bed of glowing embers. Things get real hot real fast. If the converter temperature climbs high enough, it can melt the ceramic substrate that supports the catalyst causing a partial or complete blockage inside. This increases backpressure, preventing the engine from exhaling and robbing it of power. Fuel consumption may shoot up and the engine may feel sluggish at higher speeds. Or, if the converter is completely plugged, the engine may stall after starting and not restart. There is no way to rejuvenate a dead converter or to unclog or clean out a plugged converter, so replacement is the only repair option. Up to model year 1995, converters were covered by a 5 year/50,000 mile federal emissions warranty (7 years or 70,000 miles in California). In 1995, the warranty jumped to 8 years and 80,000 miles. Replacement converters must be the same type as the original (two-way, three-way or three-way plus oxygen), EPAapproved and installed in the same location as the original. A new converter will solve a plugged or dead converter problem. But unless the underlying cause is diagnosed and corrected, the replacement converter may suffer the same fate. Other items that should also be inspected include the air pump and related plumbing, oxygen sensor and feedback control system.
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Oxygen sensors get sluggish with age, and are a leading cause of emission test failures. A sluggish oxygen sensor, for example, may not allow the fuel mixture to change back and forth quickly enough to keep the converter working at peak efficiency. Though this might not lead to a meltdown, it could cause enough of an increase in pollution to make the vehicle fail and emissions test. If the oxygen sensor has died altogether, the fuel mixture will remain fixed and the engine will probably run too rich causing an increase in fuel consumption as well as emissions. Many auto makers recommend inspecting the oxygen sensor at specific mileage intervals to prevent this kind of trouble. Some vehicles (primarily older imports from the 1980s and 1990s) have a reminder light that illuminates every 30,000 miles or so to remind the motorist to have the oxygen sensor checked or replaced. A leading supplier of oxygen sensors (Bosch) recommends replacing oxygen sensors for preventative maintenance at roughly the same interval as the spark plugs, depending on the application. Unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s applications should be replaced every 30,000 to 50,000 miles. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications should be changed every 60,000 miles. And on 1996 and newer OBD II equipped vehicles, the recommended replacement interval is 100,000 miles.
PCV PCV valves are generally considered a maintenance item like spark plugs, and should be inspected and replaced periodically (typically every 50,000 miles). The PCV valve siphons blowby vapors from the crankcase into the intake manifold so the vapors do not escape into the atmosphere. One of the beneficial effects of PCV, besides eliminating blowby emissions, is that it pulls moisture out of the crankcase to extend oil life. Moisture can form acids and sludge which can cause major engine damage. So if the PCV valve or hose plugs up, rapid moisture buildup and oil breakdown can result.
Carbon buildup under the EGR valve can cause driveability and idle problems. EGR VALVE The EGR valve has no recommended replacement or inspection interval, but that does not mean it won't cause trouble. EGR reduces the formation of oxides of nitrogen by diluting the air/fuel mixture with exhaust. This lowers combustion temperatures to keep it under 2800 degree F so little NOX is formed (the higher the flame temperature, the higher the rate at which oxygen and nitrogen react to form NOX). As an added benefit, EGR also helps prevent detonation. The heart of the system is the EGR valve. The valve opens a small passage between the intake and exhaust manifolds. When ported vacuum is applied to the EGR valve diaphragm, it opens the valve allowing intake vacuum to siphon exhaust into the intake manifold. This has a same effect as a vacuum leak, so EGR is only used when the engine is warm and running above idle speed. Some vehicles have "positive backpressure" EGR valves while others have "negative backpressure" EGR valves. Both types rely on exhaust system backpressure to open the valve. But the two types are not interchangeable. The vacuum control plumbing to the EGR valve usually includes a temperature vacuum switch (TVS) or solenoid to block or bleed vacuum until the engine warms up. On newer vehicles with computerized engine controls, the computer usually regulates the solenoid to further modify the opening of the EGR valve. Some vehicles even have an EGR valve that is driven by a small electric motor or uses solenoids rather than being vacuum-actuated for more precise control of this emission function. EGR valves do not normally require maintenance, but can become clogged with carbon deposits that cause the valve to stick or prevent it from opening or closing properly. An EGR valve that is stuck open will act like a vacuum leak and cause a rough
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idle and stalling. An EGR valve that has failed, refuses to open (or the EGR passageway i the manifold is clogged) will allow elevated NOX emissions and may also cause a detonation (spark knock) problem. Dirty EGR valves can sometimes be cleaned, but if the valve itself is defective it must be replaced. OTHER EMISSION CONTROL PARTS
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On older engines with a carburetor, one of several emission control devices may be used to reduce emissions during warm-up. Fuel vaporizes slowly when it is cold, so heating the air before it enters the carburetor or throttle body improved fuel vaporization and allows the engine to more easily maintain a balanced air/fuel mixture. Most such engines have a heated air intake system that draws warm air from a stove around the exhaust manifold into the air cleaner. A thermostat inside the air cleaner controls vacuum to a valve in the air cleaner inlet. When the engine is cold, the thermostat passes vacuum to the control valve, which closes a flap to outside air allowing heated air to be drawn into the air cleaner. As the engine warms up, the thermostat begins to bleed air, allowing the control door to open to outside air. Thus the thermostat and airflow control door are able to maintain a more consistent incoming air temperature.
One part that is often needed here is the flexible tubing that connects the air cleaner to the exhaust stove. If damaged or missing, the engine may hesitate and stumble when cold. Another early fuel evaporation aid on older V6 and V8 engines is a heat riser valve. The valve is located on one exhaust manifold. When the engine is cold, the valve closes to blocks the flow of exhaust so it will be forced back through a crossover passage in the intake manifold directly under the carburetor. The hot exhaust heats the manifold to speed fuel vaporization and engine warm-up. Once the engine warms up, the heat riser valve opens. The heat riser valve needs to be replaced if it is sticking or inoperative. On some older engines, an electrically-heated EFE grid is used under the carburetor or throttle body to aid fuel vaporization when the engine is cold. A timer turns the grid off after a fixed period of time. If the grid fails to heat (bad relay, electrical connection, etc.), the engine may hesitate and stumble when cold. Electric heater grids in the intake system are also used on some late model diesel engines for easier starting and cold performance.
Small fuel vapor leak s in the EVAP system plumbing can set a P0442 code and turn on the Check Engine light. EVAP Evaporative emissions from the fuel system (fuel vapors) are trapped and store in a charcoal canister. Later, a purge valve opens allowing the vapors to be sucked into the engine and reburned. The EVAP system usually requires no maintenance.
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The fuel filler cap is also part of the EVAP system, and is designed to keep fuel vapors from escaping into the atmosphere. A leaky or missing fuel filler cap may cause a vehicle to fail an emissions test.
OBD II Starting as early as 1994, some U.S. vehicles were equipped with a new government mandated Onboard Diagnostic (OBD II) system. By model year, 1996, OBD II was required on all new cars and light trucks. OBD II is designed to detect emission problems. When a problem is detected, the Check Engine light comes on and a diagnostic trouble code is stored in the powertrain computer (PCM). Later, the code can be read using a scan tool to determine the nature of the problem. With OBD II, the Check Engine light will come on anytime emissions exceed federal limits by 50% on two consecutive trips, or there is a failure of a major emissions control system. With earlier engine control systems, the only way to uncover most emission problems is to give the vehicle an emissions test, which is not required in many rural areas. But OBD II is on every 1996 and newer car and light truck regardless of where it is registered in the U.S. And unlike an emissions test which may only be given once every year or two, OBD II is monitoring emissions performance every time the vehicle is driven. Many areas now check emissions by performing an OBD II plug-in emissions test. The test checks to see that all the OBD II system monitors have run, that the Malfunction Indicator Lamp (MIL) is working (an OFF), and there are NO stored diagnostic trouble codes (DTCs) in the PCM's memory. Most states that do emissions testing now do a quick OBD II plug-in check rather than tailpipe testing to verify emissions compliance.
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Catalytic Converter Copyright AA1Car Catalytic converters are one of the greatest emission add-ons ever to be installed on vehicles. By cleaning up the pollutants left over from combustion, they reduce tailpipe emissions of hydrocarbons (HC) and carbon monoxide (CO) to extremely low levels, when everything is operating normally, that is. But sometimes things do not operate normally, and when that happens engine performance may suffer or the vehicle may fail an emissions test. Driveability symptoms such as a drop in fuel economy, lack of high speed power, rough idle or stalling are classic symptoms of excessive backpressure due to a plugged converter. Checking exhaust backpressure and/or intake vacuum will tell you if there's a blockage (more on this subject in a minute). Elevated HC and CO tailpipe emissions, on the other hand, are often symptoms of a fouled converter or a faulty air supply http://www.aa1car.com/library/converter.htm
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(bad or leaky air pump, diverter valve or pulse air system). A fouled converter may not cause any increase in backpressure, so other methods of checking the converter are required for this type of problem (which we'll also get to shortly). The important point to remember here is that converters don't just plug up or die for no good reason. There is usually an underlying cause which must also be diagnosed and corrected before the problem can be eliminated. Diagnosing a plugged or fouled catalytic converter is only half the fix. Replacing a bad catalytic converter will only temporarily restore things to normal because unless the underlying problem that caused the original converter to fail is identified and fixed, the replacement converter will likely suffer the same fate.
CONVERTER OPERATION Under normal operating conditions, the converter should not have to work very hard to accomplish its job. If an engine has good compression, is not sucking oil down the valve guides, and the fuel, ignition and engine management system are all working properly, there should be relatively little HC and CO in the exhaust for the converter to burn (a few tenths of a percent CO and less than 150 ppm of HC when the engine is warm). In many late-model engines with multipoint fuel injection, combustion is so clean that the converter has little to do and the difference between the inlet and outlet temperature may only be 30 degrees F at 2,500 rpm - which is a lot less than the old rule of thumb that says a good converter should show at least a 100 degree F difference fore and aft at cruise. At idle, the converter in many late-model vehicles may cool off so much that there's almost no measurable difference in fore and aft temperatures. So checking exhaust temperatures fore and aft of the converter at idle and 2,500 rpm is NOT an accurate way to determine if the converter is working properly or not. One thing temperature measurements will tell you, however, is if the converter is working too hard. An infrared noncontact pyrometer or a temperature probe will tell you if the converter is running unusually or dangerously hot. If the converter outlet temperature is 200 or more degrees higher then the inlet temperature, it means the engine is running rich and there's a lot of CO in the exhaust that needs to be burned. A rich fuel mixture will often produce a "rotten egg" odor in the exhaust (the smell is hydrogen sulfide). Underlying problems may include an engine management system that is not going into closed loop (check the coolant and oxygen sensors, or for a thermostat stick in the open position), plugged PCV valve, or excessive fuel pressure (bad fuel regulator). High CO levels in the exhaust can also be caused by an inoperative air pump system. If the outlet temperature is a lot hotter (more than 500 degrees F) than the inlet temperature, it indicates unburned fuel in the exhaust. The most likely cause would be ignition misfire (fouled spark plug, shorted or open plug wire, cracked distributor cap, arcing rotor or weak coil), or a compression leak (burned exhaust valve). But other causes may include lean misfire (check for vacuum leaks, leaky EGR valve, low fuel pressure or dirty injectors). A single misfiring spark plug can cause an increase in HC emissions of 2,500 or more parts per million, which can push the converter's operating temperature well above its normal range. A common external clue of overheating to look for is a badly discolored or warped converter shell.
CAUSES OF CATALYTIC CONVERTER PLUGGING
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Prolonged overheating or short term severe overheating are the leading causes of catalytic converter plugging. The underlying cause here is often fouled or misfiring spark plugs, or a burned exhaust valve that leaks compression and allows unburned fuel to pass through the combustion chamber into the exhaust. The average light off temperature at which the catalytic converter begins to function ranges from 400 to 600 degrees F. The normal operating temperature can range up to 1,200 to 1,600 degrees F. But as the amount of pollutants in the exhaust go up, so does the converter's operating temperature. If the temperature gets up around 2,000 degrees F or higher, several things happen. The aluminum oxide honeycomb begins to degrade and weaken. The platinum and palladium coating on the honeycomb also starts to melt and sink into the ceramic substrate reducing its effect on the exhaust. This accelerates the aging process and causes the converter to lose efficiency.
If the overheating condition persists for more than a few minutes, or if the temperature soars high enough, the honeycomb itself may melt forming a partial or complete obstruction, causing a sharp rise in backpressure. A complete blockage will cause the engine
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to stall shortly after starting, and will not allow exhaust to exit the engine. Some degree of restriction inside the converter honeycomb can also be caused by accumulated deposits: phosphorus from oil burning and/or carbon from oil burning, a rich fuel mixture or frequent short trip driving where the converter rarely reaches light-off temperature). Physical damage to the honeycomb as a result of road hazards or severe jolts may cause the relatively brittle ceramic honeycomb to break or crumble inside the converter shell. A rattling noise when you shake or thump the converter would tell you there's loose debris inside. A undamaged monolith converter should make no noise. EXHAUST BACKPRESSURE CHECKS To diagnose a plugged catalytic converter, you can check intake vacuum or exhaust backpressure. To check intake vacuum, connect a vacuum gauge to a vacuum port on the intake manifold. Start the engine and note the vacuum reading at idle. Then increase engine speed to about 2,500 rpm and hold steady. Normal vacuum at idle for most engines should be 18 to 22 inches Hg. When the engine speed is increased there should be a momentary drop in vacuum before it returns to within a couple of inches of the idle reading. If the vacuum reading is 10 percent lower than normal and/or continues to drop as the engine runs, it probably indicates a buildup of backpressure in the exhaust. Remember, though, that intake vacuum can also be affected by retarded ignition timing and valve timing. What's more, some engines are much more sensitive to small changes in intake vacuum than others, so checking backpressure rather than intake vacuum may give you a better indication of what's going on. Checking backpressure requires connecting a pressure gauge to the exhaust system. Use a gauge that reads up to 8 to 10 psi and is calibrated in 1/2 inch increments. Or, use a metric pressure gauge calibrated in kilo-Pascals (kPa). One psi equals 6.895 kPa. A backpressure gauge can be connected to the exhaust system one of several ways: by removing the oxygen sensor and connecting the gauge to the hole in the exhaust manifold; by removing the air check valve in the air pump or pulse air system and connecting the gauge here; or by drilling a small hole into the head pipe just ahead of the converter to attach the gauge (never drill a hole into the converter itself!). One drawback of drilling a hole is that the hole will have to be plugged by a self-tapping screw, plug or welded shut after you've taken your measurements. Also, drilling is not recommended if the head pipe has a double-wall construction. Once you've made your connection, start the engine and note the backpressure reading. Depending on the application, the amount of backpressure that's considered "normal" will vary. On some vehicles, backpressure should read near zero at idle, and should not exceed 1.25 psi at 2,500 rpm. Others can handle 0.5 to 1.25 psi at idle, but should have more than 4 psi during a snap acceleration test. If you find a relatively high backpressure reading (say 8 to 10 or more psi), there's obviously an exhaust restriction that will require further diagnosis. Don't jump to conclusions and assume the converter is plugged because it might be a collapsed pipe or muffler. One way to rule out the pipes and muffler is to visually inspect the exhaust system for damaged components. Another way is to drill a small hole in the pipe aft of the converter and check backpressure here. If the reading is lower (or is less than about 1 psi), the rest of the system is OK and the converter is what is causing the restriction. Or, disconnect the exhaust pipe aft of the converter. No change in backpressure would indicate a blockage at or ahead of the converter. If backpressure drops back to normal, the problem is not the converter but a collapsed pipe or muffler. If you suspect the converter is plugged, you can disconnect and remove it. Then hold a shop light by one end of the converter and look in the other end. If you can't see the light shining through the honeycomb, the converter is plugged and needs to be replaced. You can also recheck backpressure readings with the converter removed. If readings are at or near zero, you've found the problem. But if backpressure is still high, there's an obstruction in the head pipe or manifold. Sometimes a collapsed inner tube inside a double-wall head pipe will create an obstruction that acts just like a plugged converter. Another cause can be a heat riser valve on an older V6 or V8 exhaust manifold stuck in the closed position.
CONVERTER SCAN TOOL CHECKS There are several ways to detect a restricted, plugged or worn out converter using a scan tool. Here's what to look for
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* A significant difference in Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values between the right and left cylinder banks on a V6, V8 or V10 engine. If you see such a difference and the vehicle has separate converters for each cylinder bank, one of the converters may be plugged. * A lower than normal barometric pressure (BARO) value. If your engine has a Mass Airflow (MAF) sensor, and the engine computer uses the signal from the MAF sensor to calculate a barometric pressure (BARO) value, the calculated value may be lower than normal is the exhaust is restricted. * A lower than normal Manifold Absolute Pressure (MAP) sensor value. A restricted converter will cause an increase in backpressure that reduces intake vacuum. * A lower than normal Calculated Load value. The Calculated Load value (percentage or grams/second) displayed on a scan tool is a measure of the engine's volumetric efficiency. A low value means the engine isn't breathing normally because of an exhaust restriction. * A P0420 to P0423 code. The converter may not be restricted, but it is not operating at normal efficiency. The OBD II system is really good at detecting a failing or bad converter, so if everything else if working okay and there are no exhaust leaks or O2 sensor problems, and you get a P0420 code, chances are your vehicle needs a new converter.
CAUSES OF CATALYST FOULING To clean the exhaust, the catalyst inside the converter must be exposed to the hot exhaust gases. Lead, phosphorous and silicone can contaminate the catalyst and prevent it from working its magic. Lead used to be the most common contaminant, but is no more since it was eliminated from gasoline. Phosphorus is still a threat, and comes from motor oil. So if an engine is burning oil because of worn valve guides or rings, phosphorus will shorten the life of the converter. Blue smoke in the exhaust and an emissions failure are pretty good clues that the converter has been fouled with phosphorus. SJ, SM and SN rated motor oils contain less phosphorus (ZDDP) than earlier SH and earlier rated oils. ZDDP is an anti-wear additive, but less is needed in today's engines with roller lifters and cam followers. Lowering ZDDP levels reduces the risk of converter contamination over time and helps extend the life of the converter to 150,000 or more miles. Silicates can find their way into the exhaust if the engine develops an internal coolant leak through a crack in a combustion chamber or a head gasket. Silicate corrosion additives will ruin the oxygen sensor as well as the catalytic converter, so chances are if the converter has been fouled the O2 sensor will also need to be replaced. White smoke in the exhaust is a clue that there's an internal coolant leak.
CATALYTIC CONVERTER OPERATING EFFICIENCY If a converter is not plugged and passes exhaust normally, and there are no other engine performance problems (fuel, ignition and compression all OK, and the computer going into closed loop), but HC and CO levels in the exhaust are higher than they should be, the converter may be fouled. Most original equipment converters are designed for a service life of well beyond 100,000 to 150,000 miles, so if the converter has failed at low mileage contamination may be the culprit. One way to measure converter efficiency is to read the composition of the exhaust gases with a 4- or 5-gas exhaust analyzer. A number of companies sell small portable exhaust analyzers that are relatively affordable ($2,500 to $5,500) and can be used for a variety of diagnostic purposes. Plugging the HC Co and NOx readings before and after the converter into a conversion efficiency formula will reveal the condition of the catalyst. But this technique does NOT tell you if the converter will actually pass the OBD II catalyst monitor self-test. Only the OBD II system can do that. A high conversion efficiency reading in the 90 to 95 percent range for HC, CO and NOx should pass in many cases, but may not depending on how sensitive the OBD II catalyst monitor is calibrated. Checking emission readings at the tailpipe will tell you whether or not they are within normal ranges and help you diagnose the cause if emissions are high. Doing a "cold start" emissions check when the engine is first started will tell you if there are any engine problems that need attention. A cold start, in this situation, is when the converter has cooled down for at least 20 minutes. It will take a couple of minutes for the converter to warm up to light off temperature, so during this time you have a
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relatively clear window of what's coming out of the engine. When the converter reaches operating temperature, there should be a measurable drop in HC and CO readings (the amount will depend on how dirty the baseline readings were). No change in readings would indicate a dead converter. Another test is to create a momentary rich condition or a misfire (as described earlier) to see if the converter can clean it up. As the converter starts to react to the excess pollutants, it's operating temperature should go up as the tailpipe emission readings come down.
OBD II CATALYST MONITOR On 1996 and newer vehicles with OBD II onboard diagnostics, the OBD II system has a catalyst monitor to keep an eye on converter operating efficiency. The catalyst monitor may run when the vehicle is cruising at a steady highway speed of 40 to 60 mph for at least 10 minutes, or at idle depending on the vehicle application. (NOTE: The catalyst monitor will NOT run if there are any oxygen sensor fault codes present, or the oxygen sensor monitors have not completed.) The OBD II system compares O2 sensor readings upstream and downstream of the converter, and the converter's reaction time to a sudden change in the air/fuel mixture. If the converter is slow to respond, or the downstream O2 sensor readings don't flatten out and level off at 0.45 volts, it indicates a drop off in operating efficiency and sets a P0420 catalyst efficiency code. Other converter faults may set codes ranging from P0420 to P0439.
CATALYTIC CONVERTER CODES: P0420....Catalyst System Efficiency Below Threshold Bank 1 P0421....Warm Up Catalyst Efficiency Below Threshold Bank 1 P0422....Main Catalyst Efficiency Below Threshold Bank 1 P0423....Heated Catalyst Efficiency Below Threshold Bank 1 P0424....Heated Catalyst Temperature Below Threshold Bank 1 P0425....Catalyst Temperature Sensor Bank 1 P0426....Catalyst Temperature Sensor Range/Performance Bank 1 P0427....Catalyst Temperature Sensor Low Input Bank 1 P0428....Catalyst Temperature Sensor High Input Bank 1 P0429....Catalyst Heater Control Circuit Bank 1 P0430....Catalyst System Efficiency Below Threshold Bank 2 P0431....Warm Up Catalyst Efficiency Below Threshold Bank 2 P0432....Main Catalyst Efficiency Below Threshold Bank 2 P0433....Heated Catalyst Efficiency Below Threshold Bank 2 P0434....Heated Catalyst Temperature Below Threshold Bank 2 P0435....Catalyst Temperature Sensor Bank 2 P0436....Catalyst Temperature Sensor Range/Performance Bank 2 P0437....Catalyst Temperature Sensor Low Input Bank 2 P0438....Catalyst Temperature Sensor High Input Bank 2 P0439....Catalyst Heater Control Circuit Bank 2
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CATALYTIC CONVERTER WARRANTY INFORMATION If your converter needs to be replaced, it may be covered under warranty. You can take you vehicle to a new car dealer and have the converter replaced for free. However, you may be charged for other components such as oxygen sensors, pipes, clamps, etc. The federal emissions warranty that applies to ALL cars sold in the U.S. covers the catalytic converter and PCM for 8 years or 80,000 miles (which ever comes first). Some states have their own emissions warranty requirements for vehicles that are sold and registered within that state, including California, Connecticut, Maine, Massachusetts, New Jersey, New York, Rhode Island and Vermont. In these states, the converter is covered for 7 years or 70,000 miles (which ever comes first). On PZEV certified hybrid vehicles, the warranty is even better: 15 years or 150,000 miles. NOTE: Warranty coverage is from the vehicle build date, not its sale date or model year. The build date can be found on a decal or plate usually mounted on the center door pillar. Aftermarket converters have a shorter warranty of 2 years or 24,000 miles, and typically contain less catalyst and/or a shorter catalyst bed inside the converter shell. On some applications, they may not perform as well as the original and may cause the P0420 code to reset.
REPLACE CATALYTIC CONVERTER If the converter is plugged, contaminated, damaged or rusted out, it must be replaced. Likewise, if the OBD II system is showing low catalyst efficiency, the converter must be replaced. Replacing the catalytic converter will restore proper emissions performance. But a new converter will suffer the same fate as the old one if the underlying condition that caused the converter to fail has not been diagnosed and repaired. Look for fouled spark plugs or wires, low or no cylinder compression in one or more cylinders, or a computerized feedback system that stays in open loop all the time (bad coolant sensor, bad oxygen sensors, etc.). On a dual-cat system, the side with the bad converter code will tell you which cylinder bank to check. If the converter on the right is bad, for example, check the O2 sensor, spark plugs and compression on the right cylinder bank. Always replace the oxygen sensor. Converters needs an air/fuel mixture that is constantly flip-flopping from rich to lean. If the oxygen sensor is sluggish or dead, the fuel feedback loop will flip-flop too slowly or remain rich all the time. Also check the air pump (if equipped) and related plumbing as these components provide fresh air for the converter to reburn the pollutants in the exhaust. If the air pump is not working right, it can reduce the operating efficiency of the catalytic converter significantly.
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Related Articles: Troubleshooting a PO420 Catalyst Code How to Check Exhaust Backpressure How to Replace a Muffler Oxygen Sensors Oxygen Sensors & emissions
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Diagnose P0420 Catalytic Catalyst Code Copyright AA1Car Updated: Sept 21, 2013
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Your Check Engine light is on and you find a P0420 low catalyst efficiency code for your Catalytic Converter. Does that really mean your converter has reached the end of the road and needs to be replaced? A new original equipment converter can cost up to $1000 or more, while an aftermarket converter may set you back $300 or so. It's an expensive fix so you want to make sure your vehicle really needs a new converter before you replace it. A P0420 diagnostic trouble code is a "generic" fault code that is set when the Onboard Diagnostic II (OBD II) catalyst monitor detects a drop in converter efficiency. The OBD II system monitors catalyst efficiency by comparing the switching
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activity of the upstream and downstream oxygen sensors in the exhaust. The upstream O2 sensor in the exhaust manifold reacts to the exhaust gases as they exit the engine. The downstream O2 sensor in or behind the catalytic converter reacts to the exhaust gases as they exit the converter.
Catalyst Monitor Efficiency Self-Test The OBD II catalyst monitor runs a self test when certain driving conditions have been met. When this test occurs will vary depending on the year, make and model of your vehicle. The engine and converter have to be at operating temperature, and the engine may be idling or running under light load at low speed. During the catalyst self-test, the engine computer makes the air/fuel mixture rich temporarily to deplete any stored oxygen in the converter. Then the computer makes the air/fuel mixture temporarily lean to determine how long it takes for the converter to react and for the downstream O2 sensor to change its switching activity. If the converter takes too long to come back to life, it means the catalyst is not working efficiently enough to reduce emissions. The OBD II system will fail the converter, set a P0420 trouble code and turn on the Check Engine light.
Catalytic Converter Operation The catalytic converter is like an after-burner. It oxidizes (burns) any residual fuel vapors (hydrocarbons or HC) in the exhaust. It also burns any carbon monoxide (CO) in the exhaust. The exhaust must meet federal emission standards, and if a problem exists that causes emissions to exceed the federal limits by 150%, the OBD II system is supposed to catch the fault, set a code and turn on the Check Engine light. The OBD II system can't actually measure the concentration of HC or CO in the exhaust, so it compares the upstream and downstream O2 sensor readings during the catalyst monitor self-test to determine how well the catalyst is doing its job. If efficiency has dropped below the cut point the vehicle manufacturer has established for the application, the converter fails the test and a P0420 code is set. The upstream O2 sensor will undergo a lot of switching activity because the engine computer is constantly adjusting the fuel mixture between rich (more fuel) and lean (less fuel). When the engine is first started, the catalyst is cold and doesn't do anything. During this time, the switching activity of the upstream and downstream O2 sensors are essentially the same because nothing is happening inside the converter. When the converter reaches about 600 degrees F, it is hot enough to start reacting with the gases in the exhaust. This is called the catalyst's "light off" temperature. The converter now starts to clean the exhaust and remove the pollutants. This causes a sudden drop in the switching activity of the downstream O2 sensor, and the downstream O2 sensor's output voltage levels off to an average reading of around 0.45 volts. If the catalyst monitor runs its self-test and finds the converter is functioning within acceptable limits, the vehicle is in emissions compliance and no codes are set. But if the catalyst monitor finds efficiency has dropped off and the converter is slow to respond, it may set a P0420 code and turn on the Check Engine light.
Does a P0420 Code Mean You Need a New Converter? Yes, it usually means you need to replace the converter - but not always. You may have a false P0420 if your vehicle's catalyst monitor is overly sensitive. Some vehicle manufacturers have issued Technical Service Bulletins (TSBs) that involve reflashing the vehicle's engine computer so the catalyst monitor won't be quite and sensitive and slower to fail an aging converter. Other conditions may sometimes lead to a false P0420 code, such as an exhaust leak (which may fool the O2 sensors), fuel pressure problems (too high or too low), or a problem with one or more O2 sensors. But if everything else is working properly and a P0420 code is setting, the converter is not meeting emission requirements and it must be replaced to pass an emissions test. Most states now use a quick OBD II plug-in test to check emissions compliance on 1996 and newer vehicles. The plug-in test is faster, easier and cheaper to do than a loaded mode tailpipe emissions test on a road simulator or dynamometer. The rules in most states say to pass the OBD II plug-in test, the vehicle (1) must have a fully-functional OBD II system (Check Engine lamp works and the diagnostic connector communicated with the engine computer), that the Check Engine light must be off (not commanded on), and that there are no current codes in the computer's memory. Consequently, if the Check Engine light is on and you have a P0420 code (or any other code), you will FAIL the test -unless the state allows you to take an alternate tailpipe emissions test to see if your vehicle is actually polluting. Some states allow this but others do not.
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Diagnose P0420 Catalytic Coverter Code
If your state allows an alternate tailpipe test -- and your car passes -- don't worry about the converter code. Your OBD II system may be over-reacting to a perceived emissions problem that does not yet exist.
Causes of Converter Failures Under normal use, the original equipment converter on your vehicle should last upwards of 100,000 to 150,000 miles. But any number of things can make it fail prematurely. The most common cause is contamination of the catalyst because the engine is burning oil or leaking coolant internally (leaky head gasket or a crack in a combustion chamber or cylinder). Converters can also be damaged if they overheat due to ignition misfiring that allows unburned fuel to pass through into the exhaust (check for a fouled spark plug or bad plug wire). The same thing can happen if the engine has a bad exhaust valve that leaks compression into the exhaust (check compression).
Passing an Emissions Test If you live in a state that does not allow an alternative tailpipe test if your vehicle fails an OBD II plug-in test, you have to get the fault fixed to pass the test. That means replacing the converter even if it is marginal or still functional but not working well enough to make the cut point. You can't just erase the P0420 code with a scan tool prior to taking the emissions test. That will turn the Check Engine light off, but your vehicle won't be allowed to take an OBD II plug-in test until it has been driven long enough for all of the OBD II monitors (including the catalyst monitor) to have run and completed with no faults found. If the OBD Catalyst Monitor is Not Ready, you can't take the test. And if it runs and finds the same problem, it will reset the same P0420 code and turn the Check Engine light back on. So what's the fix? Nine times out of ten, a P0420 code means you have to replace your converter(s).
Aftermarket versus Original Equipment Converters Aftermarket converters are less expensive than original equipment converters (1/2 to 1/3 less!). But aftermarket converters usually contain less catalyst and have a much shorter catalyst bed inside the converter. Consequently, they are only guaranteed for 2 years or 24,000 miles - and in some cases they may not even function well enough to prevent the P0420 code from being reset! Or, they may not last until the next required emissions test. If you do opt for an aftermarket converter, get a "Direct Fit" converter that bolts right in the same as the original. "Universal" converters fit a wider range of makes and models and may be less expensive than a direct fit converter, but they often require adapters and/or cutting or modifying pipes when they are installed. Don't waste your time installing a used converter because there's no way to know what condition it might be in or how many miles are on it. Besides, used converters are now illegal to install on OBD II vehicles in some states (like California). Removing the converter and replacing it with a piece of straight pipe or a "test pipe" is also illegal, and the OBD II system will detect the missing converter anyway. Worst case scenario: you replace the converter with a new aftermarket converter, drive your car awhile and the Check Engine light comes back on. The P0420 code has returned. Now what? Clear the code, drive the vehicle until the OBD catalyst monitor runs again, and if it doesn't come on hurry up and get your vehicle inspected before the code returns. Or, redo your diagnosis to see if you missed something like an exhaust leak, fuel pressure problem or fault O2 sensor that is fooling the catalyst monitor. Or, remove the aftermarket converter and replace it with a new original equipment converter.
Oxygen Sensors For more information about oxygen sensors, see Understanding Oxygen Sensors If the downstream O2 sensor is bad (heater circuit not working, loose or corroded wiring connector, contaminated sensor element, etc.), the OBD II system should detect the fault and set an oxygen sensor code. This should prevent the catalyst monitor from running since it it needs a good signal from the upstream and downstream O2 sensors. But sometimes a faulty O2 sensor is not bad enough to set an O2 sensor code but is off just enough to affect the accuracy of the catalyst monitor.
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Exhaust Gas Recirculation (EGR)
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Exhaust Gas Recirculation (EGR) Copyright AA1Car The Exhaust Gas Recirculation (EGR) system's purpose is to reduce NOx emissions that contribute to air pollution. The first EGR systems were added to engines in 1973, and today most engines have an EGR system. As long as the EGR system is functioning properly, it should have no noticeable effect on engine performance. But if the EGR system is leaking or inoperative, it can cause driveability problems, including detonation (knocking or pinging when accelerating or under load), a rough idle, stalling, hard starting, elevated NOx emissions and even elevated hydrocarbon (HC) emissions in the exhaust. WHY EGR? Exhaust gas recirculation reduces the formation of NOX by allowing a small amount of exhaust gas to "leak" into the intake manifold. The amount of gas leaked into the intake manifold is only about 6 to 10% of the total, but it's enough to dilute the air/fuel mixture just enough to have a "cooling effect" on combustion temperatures. This keeps combustion temperatures below 1500 degrees C (2800 degrees F) to reduce the reaction between nitrogen and oxygen that forms NOx.
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HOW EGR WORKS To recirculate exhaust back into the intake manifold, a small calibrated "leak" or passageway is created between the intake and exhaust manifolds. Intake vacuum in the intake manifold sucks exhaust back into the engine. But the amount of recirculation has to be closely controlled otherwise it can have the same effect on idle quality, engine performance and driveability as a huge vacuum leak. Most older EGR systems use a vacuum regulated EGR valve while newer vehicles tend to have an electronic EGR valve to control exhaust gas recirculation. When the engine is idling, the EGR valve is closed and there is no EGR flow into the manifold. The EGR valve remains closed until the engine is warm and is operating under load. As the load increases and combustion temperatures start to rise, the EGR valve opens and starts to leak exhaust back into the intake manifold. This has a quenching effect that lowers combustion temperatures and reduces the formation of NOx. In addition to EGR, other methods may also be used to minimize NOx. These include increasing camshaft valve overlap, redesigning the combustion chamber and modifying ignition advance curves. Three-way catalytic converters also reduce NOx in the exhaust. Some engines run so clean that they do not need an EGR system to meet NOx emission standards. If the EGR system is rendered inoperative because it was disconnected or tampered with, the cooling effect that was formerly provided by the EGR system will be lost. Without EGR, the engine will often knock and ping (detonate) when accelerating or lugging the engine. This can cause engine damage over time.
TYPES OF EGR VALVES There are six different types of EGR valves: Ported EGR valves (1973 to 1980s). The typical ported vacuum EGR valve consists of a vacuum diaphragm connected to a poppet or tapered stem flow control valve. The EGR valve itself is usually mounted either on a spacer under the carburetor or on the intake manifold. A small pipe from the exhaust manifold or an internal crossover passage in the cylinder head and intake manifold routes exhaust to the valve. When vacuum is applied to the EGR valve, it opens. This allows intake vacuum to suck exhaust into the engine. To prevent the EGR valve from opening when the engine is cold, the vacuum line to the EGR valve may be connected to a parted vacuum switch or a computer-controlled solenoid. Vacuum is not allowed to pass to the valve until the engine is warm. EGR isn't needed when the engine is cold, only when it is warm and under load.
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Positive backpressure EGR valves (1973 & up). Backpressure EGR valves use exhaust backpressure to vary the point at which they open and their flow rates. On GM cars, they are identified by the last letter on the part number on top of the valve. A letter "P" indicates a positive backpressure valve, and a letter "N" indicates a negative backpressure valve. Inside a backpressure EGR valve is a second diaphragm that reacts to backpressure in the exhaust system. The backpressure diaphragm opens and closes a small bleed hole in the main EGR vacuum circuit or diaphragm chamber. Opening the bleed hole reduces vacuum to the main diaphragm and prevents the valve from opening fully. Closing the bleed hole allows full vacuum to reach the main diaphragm so the valve can open wide and allow maximum EGR flow. With positive backpressure EGR valves, any increase in exhaust backpressure causes the EGR valve to open. This reduces backpressure somewhat, allowing the backpressure diaphragm to bleed off some control vacuum. The EGR valve begins to close and exhaust pressure rises again. The EGR valve oscillates open and closed with changing exhaust pressure to maintain a sort of balanced flow. Negative backpressure EGR valves (1973 & up). The negative backpressure type of EGR valve reacts in the same way, except that it reacts to negative or decreasing pressure changes in the exhaust system to regulate EGR action. A drop in backpressure occurs when there is less load on the engine. This causes the backpressure diaphragm to open a bleed hole and reduce EGR flow. It's the same principle as with the positive type except that the control function occurs when backpressure goes down instead of up. NOTE: Most precomputer EGR systems have a temperature vacuum switch(TVS) or ported vacuum switch between the EGR valve and vacuum source to prevent EGR operation until the engine has had a chance to warm up. The engine must be relatively warm before it can handle EGR. If an engine runs rough or stumbles when cold, it may indicate a defective TVS that is allowing EGR too soon after starting. A TVS stuck in the closed position would block vacuum to the EGR and prevent any EGR operation. The symptom here would be excessive NOx emissions and possible pinging or detonation. Pulse-width modulated electronic EGR valves (early 1980s & up). First used in 1984 by General Motors, this type of EGR system uses a pulse width-modulated EGR control solenoid. With this technique, the powertrain control module (PCM) cycles the EGR vacuum control solenoid rapidly on and off. This creates a variable vacuum signal that can regulate EGR operation very closely. The amount of "on" time versus "off" time for the EGR solenoid ranges from 0 to 100 percent, and the average amount of "on" time versus "off" time at any given instant determines how much EGR flow occurs. Digital electronic EGR valves (late 1980s to 1990s). On some applications, a "digital" EGR valve is used. This type of valve also uses vacuum to open the valve but regulates EGR flow according to computer control. The digital EGR valve has three metering orifices that are opened and closed by solenoids. By opening various combinations of these three solenoids, different flow rates can be achieved to match EGR to the engine's requirements. The solenoids are normally closed, and open only when the computer completes the ground to each.
Linear electronic EGR valves (early 1990s & up). Another type of electronic EGR valve is the "linear" EGR valve. This type uses a small computer-controlled stepper motor to open and close the EGR valve instead of vacuum. The advantage of this approach is that the EGR valve operates totally independent of engine vacuum. It is electrically operated and can be opened in various increments depending on what the engine control module determines the engine needs at any given moment in time. GM started using this type of valve on many of its engines in 1992. Linear EGR valves may also be equipped with an
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EGR valve position sensor (EVP) to keep the computer informed about what the EGR valve is doing. The EVP sensor also helps with self-diagnostics because the computer looks for an indication of movement from the sensor when the it commands the EGR valve to open or close. The sensor works like a throttle position sensor and changes resistance. The voltage signal typically varies from 0.3 (closed) to 5 volts (open).
APPLICATIONS WITH NO EGR VALVE On many late model engines with Variable Valve Timing(VVT), there is no EGR valve because the VVT system varies the timing of the exhaust valves to provide the same effect as EGR. By changing the point at which the exhaust valves close when the engine is working hard under load, a small amount of exhaust gas can be retained in the cylinders for the next combustion cycle. This has the same effect on reducing combustion temperatures and NOx as recirculating exhaust gas from an exhaust port back into the intake manifold through an EGR valve. The big difference is that the VVT system can react to changing engine loads much more quickly and precisely than a traditional EGR valve. Using VVT for EGR also eliminates many of the problems associated with EGR valves such as carbon buildup and valve sticking or failure.
COMMON EGR PROBLEMS Pinging (spark knock or detonation) because the EGR system is not working, the exhaust port is plugged up with carbon, or the EGR valve has been disabled. Rough idle or misfiring because the EGR valve is not closing and is leaking exhaust into the intake manifold. You may also find a P0300 random misfire code on OBD II vehicles. Hard starting because the EGR valve is not closing and is creating a vacuum leak into the intake manifold.
EGR DIAGNOSTICS Find out what kind of EGR valve is on the vehicle so you can use the appropriate test procedure. Examine the valve or refer to a service manual. On some vehicles, you may find this information on the underhood emissions decal. Also, find out what kind of vacuum controls are used in the vacuum plumbing. Does it have a ported vacuum switch or a solenoid? Follow the vacuum connections from the valve, refer to a service manual or the underhood emissions decal for vacuum hose routing information. There are several ways to troubleshoot an EGR system. You can follow the EGR troubleshooting procedure that's listed in a service manual for the engine. On late model computer controlled engines, there may be trouble codes that relate to the EGR system. On such an application, the first step would be to read out the code or codes using a scan tool or code reader. You would then refer to the specific diagnostic charts in a service manual that tell you what to do next. EGR Trouble Codes: P0400....Exhaust Gas Recirculation Flow
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P0401....Exhaust Gas Recirculation Flow Insufficient Detected P0402....Exhaust Gas Recirculation Flow Excessive Detected P0403....Exhaust Gas Recirculation Control Circuit P0404....Exhaust Gas Recirculation Control Circuit Range/Performance P0405....Exhaust Gas Recirculation Sensor 'A' Circuit Low P0406....Exhaust Gas Recirculation Sensor 'A' Circuit High P0407....Exhaust Gas Recirculation Sensor 'B' Circuit Low P0408....Exhaust Gas Recirculation Sensor 'B' Circuit High P0409....Exhaust Gas Recirculation Sensor 'A' Circuit On pre-OBD II GM applications, a code 32 indicates an EGR problem. The logic by which the onboard diagnostics detects trouble follows one of two routes. On some applications, a code 32 is set when the computer detects a richer fuel mixture off idle (indicating no EGR). On others, a code is set if the computer energizes the EGR vacuum solenoid but does not detect a corresponding drop in intake vacuum. On pre-OBD II Fords, a code 31 indicates a problem with the EGR valve position sensor (EVP). It works like a throttle position sensor, going from high resistance (5500 ohms) when the EGR valve is closed to low resistance (100 ohms) when it is open. You'll find these EVP sensors mostly on Ford EEC-IV V6 and V8 engines. Other codes include a code 32 which indicates the EGR circuit is not controlling. A code 33 is triggered when the EVP sensor is not closing, and a code 34 indicates no EGR flow. Any of these codes could indicate a faulty EGR valve as well as a problem in the EGRC or EGRV vacuum solenoids. Other codes include a code 83 (EGRC circuit fault) and code 84 (EGRV circuit fault). Both indicate an electrical problem in one of the solenoid circuits. The solenoids should have between 30 and 70 ohms resistance.
See Emission Guide for emissions testing and diagnosis information. Emission Guide is a quick reference program that covers basic emission controls and emissions testing.
FORD EGR PROBLEMS On 1995 and newer vehicles with OBD II, P0400 to P0409 codes indicate various faults in the EGR system.
Click to see larger image of Ford DPFE sensor A common EGR problem with many Fords is a bad DPFE (differential pressure) sensor. The DPFE sensor is part of the EGR system and senses EGR flow when the EGR valve is open. It provides a feedback signal to the engine computer so it can vary EGR flow to meet changing engine loads. The DPFE sensor is usually mounted on the engine and is connected to the pipe that runs from the exhaust manifold to the EGR valve with two rubber hoses. When the sensor goes bad, the Check Engine light comes on and typically sets any or all of teh following fault codes: P0171 & P0174 (lean codes), and/or P0401 (insufficient EGR flow). Nine out of ten times, the fault is not a bad EGR valve or a vacuum leak, but a bad DPFE sensor. A
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replacement costs about $112 at Ford, or about $48 at an aftermarket auto parts store.
EGR TROUBLESHOOTING PROCEDURE The following "generic" procedure can help you troubleshoot EGR problems. 1. Does the engine have a detonation (spark knock) problem when accelerating under load? Refer to the timing specs for the engine and check ignition timing. The timing may be overadvanced. If the timing is within specs, check the engine's operating temperature. A cooling problem may be causing the engine to detonate. If the temperature is within its normal range and there are no apparent cooling problems, other possibilities to investigate include a spark plugs that are too hot for the engine application, a lean air/fuel mixture, low octane fuel or too much compression (due to a buildup of carbon in the combustion chambers or because of pistons or heads that have too much compression for the fuel you're using). Be sure you've ruled out all the other possibilities before focusing on the EGR system. 2. Use a vacuum gauge to check the EGR valve vacuum supply hose for vacuum at 2000-2500 rpm. There should be vacuum if the engine is at normal operating temperature. No vacuum would indicate a problem such as a loose or misrouted hose, a blocked or inoperative ported vacuum switch or solenoid, or a faulty vacuum amplifier (or vacuum pump in the case of a diesel engine). Sometimes loss of EGR can be caused by a failed vacuum solenoid in the EGR's vacuum supply line. Refer to a vacuum hose routing diagram in a service manual or the hose routing information on the vehicle's emission decal for the location of the solenoid. If the solenoid fails to open when energized, jams shut or open, or fails to function because of a corroded electrical connection, loose wire, bad ground, or other electrical problem, it will obviously affect the operation of the EGR valve. Depending on the nature of the problem, the engine may have no EGR, EGR all the time, or insufficient EGR. If bypassing the suspicious solenoid with a section of vacuum tubing causes the EGR valve to operate, find out why the solenoid isn't responding before you replace it. The problem may be nothing more than a loose or corroded wiring connector. 3. Inspect the EGR valve itself. Because of the valve's location, it may be difficult to see whether or not the valve stem moves when the engine is revved to 1500 to 2000 rpm by slowing opening and closing the throttle. The EGR valve stem should move if the valve is functioning correctly. A hand mirror may make it easier to watch the valve stem. Be careful not to touch the valve because it will be hot! If the valve stem doesn't move when the engine is revved (and the valve is receiving vacuum), there's probably something wrong with the EGR valve. Another way to "test" the EGR valve on some engines is to apply vacuum directly to the EGR valve. Note; This only works on ported vacuum EGR valves, not backpressure EGR valves or electronic EGR valves. Vacuum should pull the valve open creating the equivalent of a large vacuum leak. This should cause a momentary drop in idle speed and a noticeable increase in idle roughness. Backpressure type EGR valves are more difficult to check because there must be sufficient backpressure in the exhaust before the valve will open when vacuum is applied. One trick that's sometimes used is to create an artificial restriction by inserting a large socket into the tailpipe, then applying vacuum to the valve to see if it opens. Don't forget to remove the restriction afterwards. 4. Remove and inspect the EGR valve if you suspect a problem. Most failures are caused by a rupture or leak in the valve diaphragm. If the valve is not a backpressure type, it should hold vacuum when vacuum is applied with a hand-help pump. If it
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can't hold vacuum, it needs to be replaced. Note: This test does not work on backpressure EGR valves. Backpressure EGR valves sometimes fail if the hollow valve stem becomes clogged with carbon or debris. This you can see for yourself. It's almost impossible to remove such a clog, so replace the EGR valve. Carbon accumulation around the base of the EGR valve can sometimes interfere with the opening or closing of the valve. These can be removed by careful brushing or by soaking the tip of the valve in solvent. Do not soak the entire valve in solvent or allow solvent to get anywhere near the diaphragm. The solvent will attack and ruin the diaphragm. 5. Inspect the EGR passageway in the manifold for clogging. Use a pipe cleaner or small piece of wire to explore the opening for a blockage. Sometimes you can dislodge material that's clogging the opening by carefully poking at it. Other times, it may be necessary to remove the manifold and have it professionally cleaned. Also recommended is to clean the throttle body and intake manifold at the same time to remove varnish and carbon deposits.
HOW TO REPLACE EGR VALVE With so many variations from one vehicle application to the next in emission control systems and calibration, it is extremely important that you get the correct replacement EGR valve for the application. Two EGR valves may look identical but be calibrated differently in terms of flow and the amount of vacuum and/or backpressure it takes to open the valve. Therefore, you may have to refer to the vehicle's VIN number as well as year, make, model and engine size when ordering a replacement EGR valve. It may also be necessary to refer to the OEM part number on the old EGR valve (if possible) when ordering a replacement, so don't throw the old EGR valve away until you have the new one, have installed it and made sure it's working correctly. Many aftermarket EGR valves are "consolidated" so fewer part numbers are necessary to cover a wider range of vehicle applications. Some of these valves use interchangeable restricters to alter their flow characteristics. Follow the suppliers instructions as to which restricter to use for the correct calibration.
EGR Valve Service & Cleaning The following video is courtesy of Wells Manufacturing via YouTube.
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Positive Crankcase Ventilation (PCV)
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Positive Crankcase Ventilation (PCV) Copyright AA1Car The Positive Crankcase Ventilation (PCV) system reduces blowby emissions from the engine. About 20% of the total hydrocarbon (HC) emissions produced by a vehicle are blowby emissions from gases that get past the piston rings and enter the crankcase. The higher the mileage on the engine and the greater the wear on the piston rings and cylinders, the greater the blowby into the crankcase. Before PCV was invented, blowby vapors were simply vented to the atmosphere through a "road draft tube" that ran from a vent hole in a valve cover or valley cover down toward the ground. In 1961, the first PCV systems appeared on California cars. The PCV system used intake vacuum to siphon blowby vapors back into the intake manifold. This allowed the HC to be re-burned and eliminated blowby vapors as a source of pollution. The system proved to be so effective that "open" PCV systems were added to most cars nationwide in 1963. An open PCV system draws air in through a mesh filter inside the oil filler cap or a breather on a valve cover. The flow of fresh air through the crankcase helped pull moisture out of the oil to extended oil life and reduce sludge. The only drawback to these early open PCV systems was that blowby vapors could still backup at high engine speed and loads, and escape into the atmosphere through the oil filler cap or valve cover breather. In 1968, "closed" PCV systems were added to most cars. The breather inlet was relocated inside the air cleaner housing so if pressure backed up it would overflow into the air cleaner and be sucked down the carburetor. No vapors would escape into the atmosphere.
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Positive Crankcase Ventilation (PCV)
Automacit Control Valve Automatic water valve/ CHINA Automatic flow control valve
Typical PCV system. HOW PCV WORKS The major component in the PCV system is the PCV valve, a simple spring-loaded valve with a sliding pintle inside. The pintle is tapered like a bullet so it will increase or decrease airflow depending on its position inside the valve housing. The movement of the pintle up and down changes the orifice opening to regulate the volume of air passing through the PCV valve. The PCV valve is typically located in a valve cover or the intake valley, and usually fits into a rubber grommet. The location of the valve allows it to pull vapors from inside the engine without sucking oil from the crankcase (baffles inside the valve cover or valley cover deflect and help separate droplets of oil from the blowby vapors). A hose connects the top of the PCV valve to a vacuum port on the throttle body, carburetor or intake manifold. This allows the vapors to be siphoned directly into the engine without gumming up the throttle body or carburetor. Because the PCV system pulls air and blowby gases into the intake manifold, it has the same effect on the air/fuel mixture as a vacuum leak. This is compensated for by the calibration of the carburetor or fuel injection system. Consequently, the PCV system has no net effect on fuel economy, emissions or engine performance -- provided everything is working correctly. WARNING: Removing or disconnecting the PCV system in an attempt to improve engine performance gains nothing, and is illegal. EPA rules prohibit tampering with any emission control device. Disabling or disconnecting the PCV system can also allow moisture to accumulate in the crankcase, which will reduce oil life and promote the formation of engine-damaging sludge. HOW PCV FLOW CHANGES WITH ENGINE SPEED & LOAD The flow rate of a PCV valve is calibrated for a specific engine application. For the system to function normally, therefore, the PCV valve must adjust the flow rate as operating conditions change. When the engine is off, the spring inside the valve pushes the pintle shut to seal the crankcase and prevent the escape of any residual vapors into the atmosphere. When the engine starts, vacuum in the intake manifold pulls on the pintle and sucks the PCV valve open. The pintle is pulled up against the spring and moves to its highest position. But the tapered shape of the pintle does not allow maximum flow in this position. Instead, it restricts flow so the engine will idle smoothly. The same thing happens during deceleration when intake vacuum is high. The pintle is pulled all the way up to reduce flow and minimize the effect of blowby on decel emissions. When the engine is cruising under light load and at part throttle, there is less intake vacuum and less pull on the pintle. This allows the pintle to slide down to a mid-range position and allow more airflow. Under high load or hard acceleration conditions, intake vacuum drops even more, allowing the spring inside the PCV valve to push the pintle valve even lower to its maximum flow position. If blowby pressure builds up faster than the PCV system can handle it, the excess pressure flows back through the breather hose to the air cleaner and is sucked back into the engine and burned. In the event of an engine backfire, the sudden rise in pressure inside the intake manifold blows back through the PCV hose
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and slams the pintle shut. This prevents the flame from traveling back through PCV valve and possibly igniting fuel vapors inside the crankcase.
PCV MAINTENANCE Because the PCV system is relatively simple and requires minimal maintenance, it is often overlooked. The common replacement interval for many PCV valves is 50,000 miles, yet many engines have never had the PCV valve replaced. Many late model owners' manuals do not even have a recommended replacement interval listed for the PCV valve. The manual may only suggest "inspecting" the system periodically. On many 2002 and newer vehicles with OBD II, the OBD II system monitors the PCV system and checks the flow rate once during each drive cycle. But on older OBD II and OBD I systems, the PCV system is NOT monitored. So a problem with the PCV system on a pre-2002 vehicle probably won't turn on the MIL (malfunction indicator lamp) or set a diagnostic trouble code (DTC). PCV valves can last a long time, but they may eventually wear out or clog -- especially if the vehicle owner neglects regular oil changes, and sludge builds up in the crankcase. The same sludge and oil varnish that gums up the engine can also plug up the PCV valve. PCV PROBLEMS
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The most common problem that afflicts PCV systems is a plugged up PCV valve. An accumulation of fuel and oil varnish deposits and/or sludge inside the valve can restrict or even block the flow of vapors through the valve. A restricted or plugged PCV valve cannot pull moisture and blowby vapors out of the crankcase. This can cause engine-damaging sludge to form, and a backup of pressure that may force oil to leak past gaskets and seals. The loss of airflow through the valve can also cause the air/fuel mixture to run richer than normal, increasing fuel consumption and emissions. The same thing can happen if the pintle inside the PCV valve sticks shut.
If the pintle inside the PCV valve sticks open, or the spring breaks, the PCV valve may flow too much air and lean out the idle mixture. This may cause a rough idle, hard starting and/or lean misfire (which increases emissions and wastes fuel). The same thing can happen if the hose that connects the valve to the throttle body, carburetor or intake manifold pulls loose, cracks, or leaks. A loose or leaky hose allows "un-metered" air to enter the engine and upset the fuel mixture, especially at idle where the idle mixture is most sensitive to vacuum leaks. On late model vehicles with computer engine controls, the engine management system will detect any changes in the air/fuel mixture and compensate by increasing or decreasing short term and long term fuel trim (STFT and LTFT). Small corrections cause no problems, but large corrections (more than 10 to 15 points negative or positive) will typically set a lean or rich DTC and turn on the MIL. Problems can also occur if someone installs the wrong PCV valve for the application. As we said earlier, the flow rate of the PCV valve is calibrated for a specific engine application. Two valves that appear to be identical on the outside (same diameter and hose fittings) may have different pintle valves and springs inside, giving them very different flow rates. A PCV valve that flows too much air will lean the air/fuel mixture, while one that flows too little will richen the mixture and increase the risk of sludge buildup in the crankcase. Watch out for cheap replacement PCV valves. They may not flow the same as the OEM PCV valve. Quality brand name replacement PCV valves are calibrated exactly the same as the original valves, and are designed to provide long-lasting, trouble-free performance. PCV VALVE CHECKS http://www.aa1car.com/library/pcv.htm
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Positive Crankcase Ventilation (PCV)
There are a number of ways to check a PCV valve: 1. Remove the valve and shake it. If it rattles, it means the pintle inside is not stuck and the valve should flow air. But there's no way to know if the spring is weak or broken, or if a buildup of varnish and deposits inside the valve is restricting flow. 2. Check for vacuum by holding your finger over the end of the valve while the engine is idling. This test tells you if vacuum is reaching the valve, but not if the valve is flowing properly. If you don't feel vacuum, it means the valve or hose is plugged and needs to be replaced. 3. Use a flow tester to check the performance of the valve. This method is the best because it tests both vacuum and air flow. PCV SYSTEM CHECKS The volume of air that is pulled from the crankcase by the PCV system is important because it takes a certain amount of airflow to remove the blowby vapors and moisture. But too much airflow can upset the air/fuel mixture in the engine. So to check airflow, you can do any of the following: Pinch or block off the vacuum hose to the PCV valve with the engine idling at operating temperature. The engine idle rpm should typically drop about 50 to 80 rpm before the idle speed corrects itself (or you can disconnect the idle speed control motor so it won't affect idle speed during this test). If there is no change in idle speed, check the PCV valve, hose and breather tube for a restriction or blockage. A greater change would indicate too much airflow through the PCV valve. Check the part number on the PCV valve to see if it is the correct one for the engine. The wrong valve may flow too much air. If there is no part number, replace the valve with a new one (which meets OEM specifications) and test again. Measure the amount of vacuum in the crankcase. With the engine at normal operating temperature, block off the PCV breather tube or vent to the engine (usually the hose that runs from the air cleaner housing to the valve cover on the engine). Pull out the dipstick and connect a vacuum-pressure gauge to the dipstick tube. A typical PCV system should be pulling about 1 to 3 inches of vacuum in the crankcase at idle. If you see a significantly higher vacuum reading, the intake manifold gasket is probably leaking and pulling vacuum on the crankcase (replace the leaky intake manifold gasket). If you see no vacuum, or find a buildup of pressure in the crankcase, the PCV system is plugged or is not pulling enough air through the crankcase to get rid of the blowby vapors. NOTE: If the engine has a leaky oil pan, valve cover or intake manifold gasket leak, or leaky crankshaft seals, it will not be able to develop much vacuum in the crankcase because it is pulling in outside air (which is also unfiltered and can further contaminate the oil). To find a crankcase air leak, you can lightly pressurize (no more than 1 to 3 psi) the crankcase with shop air via the dipstick tube or oil filler cap or breather after blocking all the other vents. Do not use any more air pressure than this or you may create leaks where there were no leaks before. Then use a spray bottle to squirt soapy water around the gasket seams and seals. If you see bubbles, you have found an air leak (replace the gasket or seal as needed). A smoke machine also works great for finding crankcase leaks as well as vacuum leaks. A smoke machine generates a smoke-like vapor by heating mineral oil. The mist can then fed into the intake manifold to check for intake manifold vacuum leaks, or into the crankcase to check for internal engine air leaks. Any leaks will allow the smoke to escape and you will see the smoke on the outside of the engine. PCV REPLACEMENT TIPS When replacing a PCV valve, make sure the replacement valve is the same as the original. External appearances can be misleading because valves that look the same on the outside may be calibrated differently inside. If the replacement valve does not have the same flow characteristics as the original, it may upset emissions and cause driveability problems. The PCV hose that connects the PCV valve to the engine should also be replaced when the valve is changed. Use hose that is approved for PCV use only. NOTE: Can't find your PCV valve? Some engines do not have a PCV valve, but use a crankcase ventilation system with a fixed orifice oil/vapor separator. The separator functions similar to a PCV valve, but there is no movable pintle or spring inside. The separator is simply a small box with some baffles inside and a calibrated hole that allows intake vacuum to pull the blowby vapors back into the intake manifold. Like a PCV valve, the separator can plug up with varnish and sludge, http://www.aa1car.com/library/pcv.htm
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Positive Crankcase Ventilation (PCV)
causing driveability and emissions problems.
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More Emissions Articles: Exhaust Gas Recirculation (EGR) EVAP Evaporative Emission Control System Understanding OBD II Driveability & Emissions Problems Fixing Emission Failures All About Onboard Diagnostics II (OBD II) Basic Emission Control Systems Overview Exhaust Emissions Diagnosis Troubleshooting a P0420 Catalyst Code Catalytic Converters Driveability Diagnosis: Misfires Spark Knock (Detonation) Finding & Fixing Vacuum Leaks Understanding Oxygen (O2) Sensors Wide Ratio Air Fuel (WRAF) Sensors Sensing Emission Problems (O2 Sensors) Emissions testing update Evolution of I/M 240
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19/2/2015
EVAP Evaporative Emission Control System
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EVAP Evaporative Emission Control System Copyright AA1Car The Evaporative Emission Control System (EVAP) is used to prevent gasoline vapors from escaping into the atmosphere from the fuel tank and fuel system. The EVAP system usually requires no maintenance, but faults can turn on the Check Engine light and prevent a vehicle from passing an OBD II plug-in emissions test. The OBD II EVAP monitor on 1996 and newer vehicles runs diagnostic self-checks to detect fuel vapor leaks, and if it finds any (including a loose or missing gas cap), it will set a fault code and turn on the Check Engine light. However, the EVAP monitor only runs under certain operating conditions. This may create a problem for the vehicle owner if his vehicle must be given an OBD II plug-in emissions test and the monitor has not completed. Common problems with the EVAP system include faults with the purge valve that vents fuel vapors to the engine, leaks in vent and vacuum hoses, and loose, ill-fitting or missing gas caps. The most common fault code is P0440, which indicates a large leak (often a loose gas cap). EVAP Purge valve codes (P0443 to P0449) are also common). The code you don’t want to see is a P0442. This indicates the system has detected a SMALL leak, but small leaks can often be a BIG problem to find. By small, we mean a leak no larger than a pin prick! Such small leaks are virtually impossible to find visually, so a special tester called a smoke machine is usually necessary to reveal the leak. The smoke machine feeds a mineral-oil based vapor into the EVAP system under light pressure (no more than a few pounds per square inch). The smoke may also contain an ultraviolet dye to make it easier to see under UV light. Fixing EVAP codes can be a challenge, even for professional technicians. And if you have a P0442 small leak code, you’ll probably have to take your car to a repair shop that has a smoke machine.
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EVAP Evaporative Emission Control System
WHY EVAP? The EPA requires EVAP systems on cars because gasoline fuel vapors contain a variety of different hydrocarbons (HC). The lighter elements in gasoline evaporate easily, especially in warm weather. These include aldehydes, aromatics, olefins, and higher paraffins. These substances react with air and sunlight (called a photochemical reaction) to form smog. Aldehydes are often called instant smog because they can form smog without undergoing photochemical changes. The bad thing about fuel vapors is that fuel evaporates any time there is fuel in the tank. That means if the fuel system is unsealed or open to the atmosphere, it can pollute 24 hours a day even if the vehicle is not being driven. Uncontrolled evaporative emissions like this can account for as much as 20 percent of the pollution produced by a motor vehicle. The EVAP system totally eliminates fuel vapors as a source of air pollution by sealing off the fuel system from the atmosphere. Vent lines from the fuel tank and carburetor bowl route vapors to the EVAP storage canister, where they are trapped and stored until the engine is started. When the engine is warm and the vehicle is going down the road, the PCM then opens a purge valve allowing the vapors to be siphoned from the storage canister into the intake manifold. The fuel vapors are hen burned in the engine. Evaporative emission controls were first required on cars sold in California in 1970. EVAP has been used on all cars and light trucks since the early 1970s.
HOW THE EVAPORATIVE EMISSION CONTROL SYSTEM WORKS Sealing the fuel tank is not as simple as it sounds. For one thing, a fuel tank must have some type of venting so air can enter to replace fuel as the fuel is sucked up the fuel pump and sent to the engine. If the tank were sealed tight, the fuel pump would soon create enough negative suction pressure inside the tank to collapse the tank. On older EVAP systems, the tank is vented by a spring-loaded valve inside the gas cap. On newer vehicles, it is vented through the EVAP canister.
EVAP SYSTEM COMPONENTS The major components of the evaporative emission control system include: Fuel tank, which has some expansion space at the top so fuel can expand on a hot day without overflowing or forcing the EVAP system to leak. Gas cap, which usually contains some type of pressure/vacuum relief valve for venting on older vehicles (pre-OBD II), but is sealed completely (no vents) on newer vehicles (1996 & newer). NOTE: If you are replacing a gas cap, it MUST be the same type as the original (vented or nonvented). Liquid-Vapor Separator, located on top of the fuel tank or part of the expansion oerflow tank. This device prevents liquid gasoline from entering the vent line to the EVAP canister. You do not want liquid gasoline going directly to the EVAP canister because it would quickly overload the canister's ability to store fuel vapors. The liquid-vapor separator is relatively trouble-free. The only problems that can develop are if the liquid return becomes plugged with debris such as rust or scale from inside the fuel tank; if the main vent line becomes blocked or crimped; or if a vent line develops an external leak due to rust, corrosion, or metal fatigue from vibration. Some liquid-vapor separators use a slightly different approach to keeping liquid fuel out of the canister vent line. A float and http://www.aa1car.com/library/evap_system.htm
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needle assembly is mounted inside the separator. If liquid enters the unit, the float rises and seats the needle valve to close the tank vent. Another approach sometimes used is a foam-filled dome in the top of the fuel tank. Vapor will pass through the foam but liquid will cling to the foam and drip. If a blockage occurs in the liquid-vapor separator or in the vent line between it and the EVAP canister, the fuel tank will not be able to breathe properly. Symptoms include fuel starvation or a collapsed fuel tank on vehicles with solid-type gas caps. If you notice a whoosh of pressure in or out of the tank when the gas gap is removed, suspect poor venting. You can check tank venting by removing the gas cap and then disconnecting the gas tank vent line from the EVAP canister. If the system is free and clear, you should be able to blow through the vent line into the fuel tank. Blowing with compressed air can sometimes free a blockage. If not, you will have to inspect the vent line and possibly remove the fuel tank to diagnose the problem. EVAP Canister. This is a small round or rectangular plastic or steel container mounted somewhere in the vehicle. It is usually hidden from view and may be located in a corner of the engine compartment or inside a rear quarter panel. The canister is filled with about a pound or two of activated charcoal. The charcoal acts like a sponge and absorbs and stores fuel vapors. The vapors are stored in the canister until the engine is started, is warm and is being driven. The PCM then opens the canister purge valve, which allows intake vacuum to siphon the fuel vapors into the engine. The charcoal canister is connected to the fuel tank via the tank vent line. Under normal circumstances, the EVAP canister causes few problems. Since the charcoal does not wear out, it should last the life of the vehicle. The most common problem with the EVAP canister is a faulty purge control or vent solenoid. Vacuum-type purge valves can be tested by applying vacuum directly to the purge valve with a hand-held vacuum pump. The valve should open and not leak vacuum if it is good. With solenoid-type purge valves, voltage can applied directly to the solenoid to see if the valve opens. The resistance of the solenoid can also be checked with an ohmmeter to see if it is open or shorted. The purge control strategy on many late model EVAP systems can get rather complicated, so the best advice here is to look up the EVAP diagnostic procedures in the OEM service literature.
The OBD II EVAP monitor tests the fuel system for vapor leak s.
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EVAP Evaporative Emission Control System
EVAPORATIVE EMISSIONS & OBD2 On 1996 and newer vehicles, the OBD2 system monitors the fuel system for fuel vapor leaks to make sure no hydrocarbons are escaping into the atmosphere. The EVAP monitor does two things: it verifies there is airflow from the EVAP canister to the engine, and that there are no leaks in the fuel tank, EVAP canister or fuel system vapor lines. The OBD2 EVAP monitor runs once per drive cycle and only when the fuel tank is 15 to 85% full. The EVAP monitor uses a "purge flow sensor" to detect leaks as small as .040 inches in diameter on 1996-99 models, and as small as .020 inches on most 2000 and newer vehicles.
EVAP FAULT CODES If the OBD EVAP monitor detects a leak when it runs the EVAP leak check, it will set a fault code in the P0440 to P0457 range: P0440....Evaporative Emission Control System Fault P0441....Evaporative Emission Control System Incorrect Purge Flow P0442....EVAP Emission Control System Leak Detected (small leak) P0443....EVAP Emission Control System Purge Control Valve Circuit P0444....EVAP Purge Control Valve Circuit Open P0445....EVAP Purge Control Valve Circuit Shorted P0446....Evaporative Emission Control System Vent Control Circuit P0447....EVAP Emission Control System Vent Control Circuit Open P0448....EVAP Emission Control System Vent Control Circuit Shorted P0449....EVAP Emission Control System Vent Valve/Solenoid Circuit P0450....Evaporative Emission Control System Pressure Sensor P0451....EVAP Emission Control System Pressure Sensor P0452....EVAP Emission Control System Pressure Sensor Low Input P0453....EVAP Emission Control System Pressure Sensor High input P0454....EVAP Emission Control System Pressure Sensor Intermittent P0455....EVAP Emission Control System Leak Detected (gross leak) P0456....EVAP Emission Control System Leak Detected (small leak) P0457....EVAP Emission Control System Leak Detected (fuel cap) If you find a P0440, P0455 or P0457 fault code (large fuel vapor leak), remove the gas cap, inspect the seal on the filler tank inlet and the underside of the gas cap for any nicks, debris or damage. Then screw the gas cap back on and make sure it clicks at least once to assure a tight seal. If a fuel vapor leak at the gas cap set the code, the fault should clear and the Check Engine light go out the next time the EVAP monitor runs. If the light stays on, the problem is either a bad gas cap or a large vapor leak somewhere in the EVAP system (most likely a leaky or loose vapor hose).
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Evaporative Emission Control System Leak Detection Finding leaks in the EVAP system can be very difficult. It often requires using a special "smoke machine" that generates a fine mineral oil mist that is pumped into the EVAP system under very light pressure. The mist circulates through the plumbing and eventually seeps out through the leak, making the leak visible. The mist may also contain ultraviolet dye to make any leaks more visible when illuminated with a UV lamp. The following video is courtesy of Wells Manufacturing via YouTube.
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EVAP System Reference Files: EVAP Diagnostics (pdf file courtesy AC Delco) Nissan EVAP Canister TSB (pdf file courtesy Nissan) Toyota EVAP System Basics (pdf file courtesy Toyota)
More Emissions Articles: Exhaust Gas Recirculation (EGR) Positive Crankcase Ventilation (PCV) Understanding OBD II Driveability & Emissions Problems Fixing Emission Failures All About Onboard Diagnostics II (OBD II) Basic Emission Control Systems Overview Exhaust Emissions Diagnosis Troubleshooting a P0420 Catalyst Code http://www.aa1car.com/library/evap_system.htm
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Spark Knock
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Spark Knock (Detonation) Copyright AA1Car Spark Knock is a knocking, rattling or pinging noise that may be heard when he engine is accelerating or is working hard under load (driving up a hill, towing a trailer, passing on the highway, etc.). Spark knock means the fuel is detonating. Detonation is when the fuel explodes erratically instead of burning smoothly. It occurs when there is too much heat and compression in the combustion chamber. It is similar to preignition, but preignition is when the fuel ignites before the spark occurs because of a hot spot inside the combustion chamber. Preignition can burn a hole right through the top of a piston (see photo above). Detonation is very bad for your engine because over a long period of time it may cause the head gasket to fail, the rings to break, piston lands to crack and/or rod bearing damage. CAUSES OF SPARK KNOCK The things that usually cause spark knock (detonation) are: (1) The EGR valve that is not working. The EGR valve is supposed to open when the engine is accelerating or lugging under a load. This allows intake vacuum to suck some exhaust in through the EGR valve to dilute the air/fuel mixture slightly. This lowers combustion temperatures and prevents knock. Inspect the operation of the EGR valve, and check for a buildup of
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Spark Knock
carbon deposits on the valve pintle or valve port that may be blocking the flow of exhaust back into the engine. Clean off the carbon deposits with a wire brush and carburetor cleaner, or replace the EGR valve if it is defective. (2) A bad knock sensor. Your engine has a knock sensor that should detect detonation and tell the computer to retard the ignition timing. If your engine requires premium grade fuel, but you are using regular or mid-grade fuel, the knock sensor should detect any detonation that may occur when the engine is working hard under a load and cause the PCM to retard timing. This reduces power a bit but protects your engine against detonation. However, if the knock sensor is not working, spark timing will not retard when it should. Consequently, you may hear a pinging or rattling sound (spark knock) when accelerating, driving up a hill, or when the engine is lugging under a heavy load.
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The knock sensor can be tested by tapping on the engine near the sensor (not the sensor itself) with a wrench while watching spark timing Professional Export Services Provided and/or knock sensor input on a scan tool to see if it sends a timing retard signal.
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NOTE: Overadvanted ignition timing can also cause the same thing (spark knock). But on most late model engines, ignition timing is not adjustable and is controlled by the engine computer. The only way to change the timing advance would be to flash reprogram the PCM. (3) Excessive carbon buildup in the combustion chambers and on the tops of the pistons. This is usually more of an issue with older, high mileage engines or vehicles that are only driven for short trips and never fully warm up. Treating the engine with a dose of top cleaner or a fuel system additive that also removes carbon from the combustion chamber can usually clears this up. Some repair shops use a machine called a MotorVac to perform an engine carbon cleaning procedure. The machine uses a concentrated detergent to flush out the fuel injection system and combustion chambers. (4) Compression ratio too high. If an engine has been rebuilt and the cylinders have been bored to oversize, it will increase the engine's static compression ratio. Or, if the cylinder head has been resurfaced to restore flatness, this will reduce the volume of the combustion chamber and also increase the engine's static compression ratio. These changes will increase engine power, but also the risk of detonation on regular 87 octane fuel. Such modifications may require using higher octane 89 or 93 octane premium fuel and/or retarding spark timing. Engines that are supercharged or turbocharged are also at much higher risk of detonation because the forced air induction system increases compression. This usually requires using premium fuel. (5) Low octane gas. Regular grade gasoline is supposed to have an octane rating of 87. If the gas station or their refiner is cutting corners and the fuel is not 87, it may cause spark knock. The fix for this is to try a tank of mid-range or premium gasoline. Be warned, though, that some stations cheat on this too, and don't always give you the octane rating claimed on the pump. Premium gas costs more, but your engine may need it to reduce the knocking. Or, if you always buy gas at the same gas station, try a different gas station. Don't buy the cheapest gas you can find. BP, Shell and Mobil are all good brands. (6) Engine overheating. If the engine is running too hot because of low coolant, a cooling fan that isn't working, a plugged radiator, bad water pump, sticking thermostat, etc., it may cause the fuel to detonate. (7) Too much turbo boost. If your engine is turbocharged, excessive boost pressure can cause detonation and engine damage. Boost pressure is controlled by the engine computer, a Manifold Absolute Pressure (MAP) sensor, and a device called a "wastegate" that opens to vent pressure produced by the turbo when it exceeds a preset level. If the MAP sensor is not reporting boost pressure to the computer correctly, or the computer is not processing the sensor inputs correctly, or the wastegate is not opening, the engine can experience over-boost, detonation and possible damage. (8)Lean fuel mixture. A lean fuel mixture (too much air/not enough fuel) is more likely to experience detonation than a normal fuel mixture or a rich fuel mixture. A lean fuel mixture may be caused by dirty fuel injectors, low fuel pressure (possibly due to a leaky fuel pressure regulator or a weak fuel pump), engine air/vacuum leaks, or a faulty Mass Airflow (MAF) sensor.
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Detonation
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Detonation Copyright AA1Car Detonation (also called "spark knock") is an erratic form of combustion that occurs when multiple flame fronts occur simultaneously inside your engine's combustion chambers. Instead of a single flame front expanding outward from the point of ignition, multiple flame fronts are generated spontaneously throughout the combustion chamber. As the multiple flame fronts collide, they produce the sharp metallic pinging or knocking noise that warns you nasty things are taking place. If your engine has a detonation problem, you'll be most apt to hear it when accelerating under load, when giving the engine gas when you are in a high gear or when lugging the engine. Detonation occurs because the fuel's octane rating(a measure of its detonation resistance) can't handle the elevated heat and pressure when the engine comes under load. When that happens, the fuel mixture autoignite creating the destructive multiple flame fronts. Mild detonation can occur in almost any engine and won't cause any harm. But prolonged heavy detonation is bad news because it hammers the pistons and rings. If the problem is not corrected, severe detonation may damage your engine. It can crack pistons and rings, cause the head gasket to fail, damage spark plugs and valves, and even flatten rod bearings. Detonation also results in a loss of power because the rise in cylinder pressure occurs too rapidly for an efficient power stroke. Instead of building gradually, it peaks quickly then drops off. The result is more like a sudden blow instead of a strong, steady push.
PREVENT DETONATION WITH HIGHER OCTANE GASOLINE
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Detonation
One way to prevent detonation is to use a higher octane fuel. The octane rating of a motor fuel is a measure of its detonation resistance. The octane that IS posted on the filling station pump is "pump octane," which is an average of research and motor octane ratings. The method of determining a fuel's octane number varies depending on the technique used, but the higher the octane number the better able the fuel is to resist detonation. A gasoline's octane rating can be improved by additional refining to increase the proportion of heavier hydrocarbons in the fuel, by using a higher grade crude stock or by adding ethanol alcohol as an octane booster (all of which may increase the cost of the fuel). Tetraethyl lead was long used as an anti-knock additive to improve gasoline octane. It was the most effective and least expensive additive that could be used for this purpose. But prolonged exposure to lead has been associated with numerous health risks. Leaded gasoline was phased out in the U.S. back in the 1970s, so increased refining (cracking, isomerization and other processes) are used to raise the octane rating of the base gasoline. Additional octane boosters such as MBTE, ethanol alcohol, aromatics and highly branched alkanes are now added to gasoline to meet octane requirements for adequate detonation resistance.
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AFTERMARKET OCTANE BOOSTING FUEL ADDITIVES If you drive an older muscle car and can't find pump gas with a high enough octane to prevent detonation in your engine, and you don’t want to detune your engine by retarding spark timing or reducing its compression ratio, you can add an aftermarket octane boosting fuel additive to the fuel tank. Some octane boosting additives also contain lead or lead substitutes to protect the exhaust valves in pre-1973 engines (which lack hardened valve seats) from premature wear. Such products can boost the octane rating of pump gas several points depending on the concentration used (always follow directions). But even this might not be enough to eliminate a persistent spark knock problem if your engine has a compression ratio over 10:1, or is supercharged or turbocharged.
WHAT CAUSES DETONATION? Detonation can have multiple causes. Anything which increases combustion temperatures or pressures, or increases the engine’s operating temperature, or overadvances spark timing, or causes the air/fuel mixture to run leaner than normal may cause detonation. Some engines require premium fuel (91 or higher octane) and may experience detonation if you fill the tank with mid-range or regular grade fuel. Under light throttle the engine may run fine on the less expensive fuel, but during hard acceleration or when lugging the engine under load, detonation may occur. The knock sensor is supposed to detect the vibrations that signal detonation is occurring and retard spark timing temporarily until the detonation stops. Even so, it may not prevent detonation entirely. Our advice is to use the grade of gasoline recommended in the owners manual or printed on the fuel filler cap to minimize the risk of detonation. Other causes of detonation may include any of the following:
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Too much compression can cause detonation. An accumulation of carbon deposits in the combustion chambers, on piston tops and valves can increase compression to the point where it causes detonation. Carbon deposits can also cause "preignition" which is a condition where hot spots in the combustion chamber become ignition points, causing the fuel to ignite before the spark plug fires. Preignition is also what makes an engine run on after the ignition has been turned off. How quickly the deposits accumulate depends on the type of driving done and the quality of the fuel burned. Carbon deposits gradually accumulate in a new engine for the first 5,000 to 15,000 miles, then level off. A state of equilibrium is reached where old deposits flake off at about the same rate as new deposits are formed. Infrequent driving, infrequent oil changes or internal engine problems such as worn valve guides, or worn, broken or improperly seated rings that allow oil burning can greatly accelerate the accumulation of deposits. To get rid of the deposits, pour a can of "top cleaner" down the carburetor or through the throttle body while the engine is idling (follow the directions on the product). Allow the chemical to soak the recommended period of time, then restart the engine and blow out the crud (an oil change afterwards is recommended). Repeat as need if the first cleaning fails to eliminate the detonation problem. If chemical cleaning fails to remove the carbon, there is always the "Italian Tuneup" method of blowing the carbon out of the engine. Take your vehicle somewhere where there is little or no traffic and you can safely accelerate at full throttle up to the posted speed limit (or beyond if you don’t mind risking a speeding ticket). Repeat this several times, then cruise at highways speeds for at least 15 minutes to clean the carbon out of the combustion chambers. If a high mileage engine is so badly carboned up that chemical cleaning and/or hard driving can’t get the carbon out, another option is to use a "soft" blasting media such as crushed walnut shells to scour the combustion chambers clean. This job can be done with the cylinder head in place by removing the spark plug, blowing the media in through the plug hole to knock loose the carbon, then sucking out the debris with a shop vacuum. If your engine has a static compression ratio that is higher than 10:1, the only way to totally eliminate a detonation problem on pump gas may be to rebuild the engine with lower compression pistons, or cylinder heads with larger combustion chambers, or to replace the stock head gasket with a thicker head gasket to reduce the compression ratio!
Over-advanced ignition timing can cause detonation. Too much spark advance causes cylinder pressure to rise too rapidly. On older vehicles with a mechanical distributor, rotating the distributor to retard timing several degrees and/or changing the spark advance springs so timing does not advance as quickly can reduce the risk of detonation, but it will also hurt performance. On newer vehicles with electronic spark timing, it may be possible to change the spark advance curve with a special tuner scan tool.
Engine overheating can cause detonation. A hot engine is more likely to suffer spark knock than one which runs at normal temperature. Overheating can be caused by a low coolant level (check for coolant leaks), a defective fan clutch, an undersized fan or missing fan shroud, an electric cooling fan, fan relay or temperature sensor that is not working properly, a thermostat that is sticking shut, a bad water pump, a clogged radiator, or a severe restriction in the exhaust such as a clogged catalytic converter that is backing heat up into the engine. Poor heat conduction inside the engine due to rust or scale accumulation inside the engine’s cooling jackets can also make an engine run hot. Check the operation of the cooling fan (electric fans should come on when the A/C is turned on), and check for coolant leaks. Check the condition of the coolant. If dirty, add a bottle of cooling system cleaner to the cooling system, run for the specified period of time, then drain and flush the cooling system.
Overheated air can cause detonation. On older vehicles with carburetors, the thermostatically controlled air cleaner provides hot air to aid fuel vaporization during engine warm-up. If the air control door sticks shut so that the carburetor continues to receive heated air after the engine is warm, the engine may experience detonation, especially during hot weather. Check the operation of the air flow control door in the air cleaner to see that it opens as the engine warms up. No movement may mean the vacuum motor or thermostat is defective. If you have an open style air cleaner on an older engine with a carburetor, or a "cold air" intake on a newer fuel injected engine, the intake may be pulling in heated air from the engine compartment. To reduce the risk of detonation, you want cooler, denser air from outside the engine compartment or ahead of the radiator entering the intake system.
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Detonation
Lean fuel mixtures can cause detonation. Rich fuel mixtures resist detonation while lean ones do not. Air leaks in vacuum lines, intake manifold gaskets, carburetor or throttle body gaskets, or intake manifold gaskets can allow extra air to enter the engine. Lean fuel mixtures can also be caused by dirty fuel injectors, carburetor jets clogged with fuel deposits or dirt, a restricted fuel filter or a weak fuel pump. If the fuel mixture becomes too lean, "lean misfire" may also occur as the load on the engine increases. This can cause hesitation, stumble and a rough idle condition. The air/fuel ratio can also be affected by changes in altitude. As you go up in elevation, the air becomes less dense. A carburetor that is calibrated for high altitude driving will run too lean if driven at a lower elevation. Altitude changes are generally not a problem with late model feedback carburetors and electronic fuel injection because the oxygen and barometric pressure sensors compensate for changes in air density and fuel ratios.
A piston destroyed by preignition because the air/fuel mixture went too lean under hard load. The wrong spark plugs can cause detonation. Spark plugs with the wrong heat range (too hot) can cause detonation as well as preignition. Copper core spark plugs have a broader heat range than ordinary spark plugs, which lessens the danger of detonation.
Loss of EGR can cause detonation. Exhaust gas recirculation (EGR) has a cooling effect on combustion temperatures because it dilutes the incoming mixture with inert exhaust gas. This lowers combustion temperatures and reduces the formation of oxides of nitrogen (NOX). It also reduces the risk of detonation. So if the EGR valve is not working or someone has disconnected it or plugged the EGR vacuum hose, combustion temperatures will run much higher likely resulting in detonation when the engine is under load.
Excessive turbo boost can cause detonation. Controlling the amount of boost in a turbocharged engine is absolutely critical to prevent detonation. The turbo wastegate bleeds off boost pressure in response to rising intake manifold pressure. On most late model engines, a computer controlled solenoid helps regulate the operation of the wastegate. A malfunction with the manifold pressure sensor, the wastegate control solenoid, the wastegate itself or a leak in the vacuum connections between these components can allow the turbo to deliver too much boost, which will send the engine into early retirement if the condition is not corrected. Improved intercooling can also help. The intercooler's job is to lower the incoming air temperature after it exits the turbo compressor. Adding an intercooler to a turbo motor that isn't intercooled can eliminate detonation worries while also allowing the engine to handle more boost. And if a factory turbo motor has been tweaked, replacing the stock intercooler with a larger, more efficient aftermarket intercooler may be necessary to prevent detonation.
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A bad knock sensor can cause detonation. Many late model engines have a "knock sensor" on the engine that responds to the frequency vibrations characteristically produced by detonation (typically 6-8kHz). The knock sensor produces a voltage signal that signals the computer to momentarily retard ignition timing until the detonation stops. A knock sensor can usually be tested by rapping a wrench on the manifold or cylinder head near the sensor (never hit the sensor itself!) and watching for the timing to change while the engine is idling. If the timing fails to retard, the sensor may be defective or the problem may be within the electronic spark timing control circuitry of the computer itself. Sometimes a knock sensor will react to sounds other than those produced by detonation. A noisy mechanical fuel pump, a bad water pump or alternator bearing, or a loose rod bearing can all produce vibrations that can trick a knock sensor into retarding timing.
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HOW ELECTRONIC FUEL INJECTION WORKS
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How Electronic Fuel Injection Works Copyright AA1Car Electronic fuel injection (EFI) replaced carburetors back in the mid-1980s as the preferred method for supplying air and fuel to engines. The basic difference is that a carburetor uses intake vacuum and a pressure drop in the venturi (the narrow part of the carburetor throat) to siphon fuel from the carburetor fuel bowl into the engine whereas fuel injection uses pressure to spray fuel directly into the engine. With a carburetor air and fuel are mixed together as air is pulled through the carburetor by the engine. The air/fuel mixture then travels through the intake manifold to the cylinders. One of the drawbacks of this approach is that the intake manifold is wet (contains droplets of liquid fuel) so fuel can puddle in the plenum area of the manifold when a cold engine is first started. The twists and turns of the intake runners can also cause the air and fuel mixture to separate as if flows to the cylinders, resulting in uneven fuel mixtures between cylinders. The center cylinders typically run slightly richer than the end cylinders, which makes tuning for peak fuel economy, performance and emissions more difficult with a carburetor. THROTTLE BODY INJECTION With Throttle Body Injection (TBI), one or two injectors mounted in the throttle body spray fuel into the intake manifold. Fuel pressure is created by an electric fuel pump (usually mounted in or near the fuel tank), and the pressure is controlled by a regulator mounted on the throttle body. Fuel is sprayed into the engine when the engine computer energizes the injector(s), which occurs in a rapid series of short bursts rather than a continuous stream. This produces a buzzing noise from the injectors when the engine is running. Because of this setup, the same fuel distribution issues that affect carburetors also affect TBI systems. However, TBI systems have better cold start characteristics than a carburetor because they provide better atomization and do not have a troublesome choke mechanism. A TBI system also makes it easier for an electronic engine control system to regulate the fuel mixture than an electronic feedback carburetor. Throttle Body Injection systems were only used briefly during the 1980s as US vehicle manufacturers transitioned from carburetors to fuel injection to meet emission regulations. By the late 1980s, most TBI systems were replaced with Multiport Injection (MPI) fuel injection systems.
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MULTIPORT FUEL INJECTION With MultiPort Injection systems, there is a separate fuel injector for each cylinder. The advantage of this approach is that fuel is sprayed directly into the cylinder head intake port. Since only air flows through the intake manifold, the intake manifold remains dry and there are no problems with fuel puddling when the engine is cold or fuel separation causing uneven fuel mixtures in the center and end cylinders. This allows the fuel mixture to be much more even in all of the cylinders for better fuel economy, emissions and performance. Some early production multiport fuel injection systems were purely mechanical and date back to the 1950s (1957 Corvette with Rochester Fuel Injection , for example, and Bosch D-Jetronic and K-Jetronic systems with their mechanical fuel distributors and injectors). Later fuel injection systems such as the Bosch L-Jetronic systems of the late 1970s replaced mechanical injectors with electronic injectors. Today, all production EFI systems are fully electronic with computer controls and electronic injectors. Most of the EFI systems that were offered in the late 1980s and early 1990s fire all of the injectors simultaneously, typically once every revolution of the crankshaft. The more sophisticated Sequential Fuel Injection (SFI) systems that came later fire each injector separately, usually just as the intake valve is opening. This allows much more precise fuel control for better fuel economy, performance and emissions. GASOLINE DIRECT FUEL INJECTION In the 2000s, some vehicle manufacturers began offering a new type of fuel injection system called Gasoline Direct Injection (GDI). With this setup, a separate injector is still used for each cylinder but the injectors are relocated on the engine to spray fuel directly into the combustion chamber rather than the intake port. This is similar to a diesel engine that sprays fuel directly into the cylinder. The advantage with this approach is a significant improvement (as much as 15 to 25 percent!) in fuel economy and power. However, it requires special high pressure fuel injectors and much higher operating pressures. Some current examples of direct fuel injection include VW TDI engines, Mazda direct injection engines, General Motors EcoTech engines and Ford EcoBoost engines.
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FUEL INJECTOR PULSES The relative richness or leanness of the fuel mixture in a fuel injected engine is determined by varying the duration of the injector pulses (called pulse width). The longer the pulse width, the greater the volume of fuel delivered and the richer the mixture. Injector timing and duration is controlled by the engine computer. The computer uses input from its various engine sensors to regulate fuel metering and to change the air/fuel ratio in response to changing operating conditions. The primary sensor for fuel mixture control is the Oxygen sensor. The O2 sensor generates a RICH or LEAN signal that the engine computer uses to adjust the fuel mixture. For more information about feedback fuel control and fuel trim adjustments, see What Is Fuel Trim? The computer is calibrated with a fuel delivery program that is best described as a three-dimensional map. The program directs the computer as to how long to make the injector pulses as engine speed and load change. During start-up, warm-up, acceleration and increased engine load, the map typically calls for a richer fuel mixture. When the engine is cruising under light load, the map allows for a leaner fuel mixture to improve fuel economy. And when the vehicle is decelerating and there is no load on the engine, the map may allow the computer to momentarily turn the injectors off altogether. The programming that controls the EFI system is contained on a PROM (Program Read Only Memory) chip inside the engine computer. Replacing the PROM chip can change the calibration of the EFI system. This is sometimes necessary to update factory programming or to correct a drivability or emissions problem. The PROM chip on some vehicles can also be replaced with aftermarket performance chips to improve engine performance, too. On many 1996 and newer vehicles, the programming is on an EEPROM (Electronically Ereasable Program Read Only Memory) chip in the computer. This allows the programming to be updated or changed by reflashing the computer. The new programming is downloaded into the computer through the OBD II Diagnostic Connector using a scan tool or J2534
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HOW ELECTRONIC FUEL INJECTION WORKS
reprogramming tool. EFI SENSOR INPUTS Electronic fuel injection requires inputs from various engine sensors so the computer can determine engine speed, load and operating conditions. This allows the computer to adjust the fuel mixture as needed for optimum engine operation. There are two basic types of EFI systems: Speed-Density systems and Mass Airflow systems. Speed density systems such as those found on many Chrysler engines and some GM engines do not actually measure airflow into the engine, but estimate airflow based on inputs from the Throttle Position Sensor (TPS), Manifold Absolute Pressure (MAP) sensor and engine RPM. The advantage with this approach is that the engine does not require an expensive airflow sensor, and the air/fuel mixture is less affected by small air leaks in the intake manifold, vacuum plumbing or throttle body.
A Ford mass airflow sensor also includes an Inlet Air Temperature (IAT) sensor inside. With mass airflow systems, some type of airflow sensor is used to directly measure airflow into the engine. It may be a mechanical flap style airflow sensor, a hot wire airflow sensor or a vortex airflow sensor. The computer also uses inputs from all of its other sensors, but relies primarily on the airflow sensor to control the fuel injectors. An EFI system will usually run without a signal from the MAP sensor, but it will run poorly because the computer has to rely on its other sensor inputs to estimate airflow. A common problem with MAF sensors is a buildup of dirt or varnish on the heated wire inside the sensor. Cleaning the MAF wire inside the sensor with electronics cleaner will often restore normal operation and cure a lean condition caused by a dirty airflow sensor. On both types of systems (speed-density and mass airflow), input from the Heated Oxygen sensor (HO2) is also key for maintaining the optimum air/fuel ratio. The oxygen sensor (or Air/Fuel sensor on many newer vehicles) is mounted in the exhaust manifold and monitors unburned oxygen levels in the exhaust as an indicator of the relative richness or leanness of the fuel mixture. On V6 and V8 engines, there will be a separate oxygen sensor for each bank of cylinders, and on some straight six cylinder engines (BMW for example), there may be separate oxygen sensors for the first three cylinders and the last three cylinders. The feedback signal from the oxygen sensor or air/fuel sensor is used by the engine computer to constantly fine tune the fuel mixture to optimum fuel economy and emissions. When the oxygen sensor tells the computer the engine is running lean (higher levels of unburned oxygen in the exhaust), the computer compensates by richening up the fuel mixture (increasing the pulse width of the injectors). If the engine is running rich (less oxygen in the exhaust), the computer shortens the pulse width of the injectors to lean the fuel mixture. Input about the position of the throttle is provided by the Throttle Position Sensor (TPS). It is located on the side of the throttle body and uses a variable resistor that changes resistance as the throttle opens and closes. Engine load is measured by the Manifold Absolute Pressure (MAP) sensor. It may be mounted on the intake manifold or attached to the intake manifold with a vacuum hose. The temperature of the air entering the engine must also be monitored to compensate for changes in air density that occur (colder air is denser than hot air). This is monitored by an Inlet Ait Temperature (IAT) or Manifold Air Temperature (MAT) http://www.aa1car.com/library/fuel_injection_basics.htm
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sensor, which may be built into the airflow sensor or mounted separately on the intake manifold. Coolant temperature is monitored by the Coolant Temperature Sensor (CTS). This tells the computer when the engine is cold and when it is at normal operating temperature. The computer needs to know the temperature because a cold engine requires a richer fuel mixture when it is first started. When the coolant reaches a certain temperature, the engine goes into Closed Loop operation, which means it starts using inputs from the oxygen sensors to fine tune the fuel mixture. When it is operating in Open Loop (when cold or when there is no signal from the coolant sensor), the fuel mixture is fixed and does not change. Faulty inputs from any of the engine's sensors may cause drivability, emissions or performance problems. Many sensor problems will set a Diagnostic Trouble Code (DTC) and turn on the Check Engine Light. Reading the code(s) with a scan tool will help you diagnose the problem.
EFI throttle body. IDLE SPEED CONTROL Idle speed on fuel injected engines is computer controlled via an idle air bypass circuit on the throttle body. A small electric motor or solenoid is used to open and close the bypass orifice. The larger the opening, the greater the volume of air that can bypass the throttle plates and the faster the idle speed. On newer vehicles with electronic throttle control, the computer also controls the opening of the throttle plate when the driver pushes down on the gas pedal. Position sensors in the gas pedal signal the computer how far to open the throttle plate. Idle problems on EFI systems can be caused by varnish and dirt deposits in the throttle body idle control circuit. Cleaning the throttle body with throttle body cleaner can often solve idle problems (follow the directions on the product). Idle problems can also be caused by air leaks between the airflow sensor and throttle, the throttle body and intake manifold, and the intake manifold and cylinder head(s), or in the PCV or EGR systems, or vacuum hoses.
On most EFI systems, voltage is supplied directly to the injectors and the PCM energizes the injector by grounding the circuit. INJECTORS A fuel injector is nothing more than a spring-loaded solenoid pintle valve. When energized by the computer, the solenoid pulls the valve open. This allows fuel to spray out of the nozzle and into the engine. When the computer cuts the circuit that powers the injector, the valve inside the injector snaps shut and fuel delivery stops. The total amount of fuel delivered is controlled by cycling the injector voltage on and off very rapidly. The longer the pulse width, the greater the volume of fuel delivered and the richer the fuel mixture. Decreasing the duration of the injector signal pulse reduces the volume of fuel delivered and leans out the mixture. Dirty fuel injectors are a common problem. A buildup of fuel varnish deposits inside the tip of the injector spray nozzle can restrict fuel delivery and interfere with the creation of a good spray pattern. This can cause a lean fuel condition and misfiring. Cleaning the injectors with fuel injection cleaner, or removing the injectors and having them cleaned on a fuel injector cleaning
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HOW ELECTRONIC FUEL INJECTION WORKS
machine can usually restore normal operation. Using a Top Tier gasoline that contains adequate levels of injector cleaner can also prevent varnish deposits from forming.
The fuel pressure regulator is usually mounted on the fuel rail that supplies the injectors. FUEL PRESSURE CONTROL Another important factor that helps determine how much fuel is delivered through an injector when it is pulsed, and that is the fuel pressure behind it. The higher the pressure behind the injector, the greater the volume of fuel that will spray out of the injector when it is opened. Fuel pressure is generated by a high pressure electric fuel pump usually mounted inside or near the fuel tank. Pump output pressure may range anywhere from 8 to 80 lbs. depending on the application. The pump usually has an pressure valve to vent excess pressure and a check valve to maintain system pressure when the ignition is off. In a multiport EFI system, the pressure differential between the fuel behind the injectors and the vacuum or pressure in the intake manifold is a constantly changing variable. Under light load or at idle, a relatively high vacuum exists in the intake manifold. This means less fuel pressure is needed to spray a given volume of fuel through the injector. Under heavy load, engine vacuum drops to near zero. Under these circumstances, more pressure is needed to deliver the same quantity of fuel through the injector. And in turbocharged engines, manifold vacuum can become 8 to 14 lbs. of positive pressure when turbo boost comes into play. Even more fuel pressure is required to force the same amount of fuel through the injector. A means of regulating fuel pressure according to engine vacuum must be provided in a multiport EFI system to maintain the same relative pressure differential between the fuel system and intake manifold. This is done by the fuel pressure regulator. The regulator is mounted on the fuel rail that supplies the injectors. On returnless EFI systems, the regulator is part of the fuel pump assembly inside the fuel tank. The fuel pressure regulator has a simple spring-controlled vacuum diaphragm with a vacuum connection to the intake manifold. The regulator decreases fuel pressure under light load and increases it under heavy load or boost conditions. The excess fuel pressure is shunted through a bypass port back to the fuel tank to maintain the desired pressure differential. Most systems are calibrated to maintain a pressure differential of somewhere between 40 and 55 psi. On the older TBI systems, the regulator has an easier job because the injectors are mounted above the throttle plates. Since engine vacuum/boost has no effect on fuel delivery out of the injector on the TBI system, regulator only has to maintain an even pressure. On General Motors TBI applications, the pressure regulator is calibrated to maintain roughly 10 psi in the fuel system but most others run close to 40 psi. Low fuel pressure will result in poor engine performance, possible misfiring and may prevent the engine from starting. Low fuel pressure can be caused by a weak fuel pump (a worn pump or low voltage to the pump that caused it to run slowly), restrictions in the fuel line, a plugged fuel filter, or a leaky fuel pressure regulator. Fuel pressure MUST be within specifications for the engine to run properly. Fuel pressure can be tested with a fuel pressure gauge connected to the service valve on the fuel rail, or teed into the fuel line.
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Fuel Trim?
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Fuel Trim Copyright AA1Car
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. Fuel Trim is the adjustment the engine computer (PCM) makes to the fuel mixture to maintain a balanced air/fuel ratio. Fuel trim is usually displayed as a PERCENTAGE reading on a scan tool. For lowest emissions, the engine computer tries to keep the fuel mixture balanced around 14.7 to 1 (14.7 parts of air to one part fuel). If the air/fuel ratio is less than 14.7 to one (say 12 to 1), the fuel mixture is RICH. A rich fuel mixture can produce more power (up to a point) but it also increases fuel consumption and emissions. Conversely, if the fuel mixture is greater than 14.7 to one (say 16 to one), it is LEAN. A lean fuel mixture reduces fuel consumption but can also increase emissions if the air/fuel mixture is so lean that it fails to ignite and causes lean misfire. The engine computer monitors the air/fuel ratio via the oxygen sensor(s) in the exhaust manifold(s). An oxygen sensor is essentially a RICH or LEAN indicator. When the engine is running lean (too much air and not enough fuel), the O2 sensor generates a low voltage signal that tells the engine computer more fuel is needed. When the engine is running rich (too much fuel and not enough air), the O2 sensor produces a higher voltage signal that tells the engine computer the engine is getting too much fuel and to cut back the fuel delivery. On vehicles that have an Wide Ratio Air/Fuel sensor (WRAF) or A/F sensor, the sensor tells the computer the exact air fuel sensor so the computer can increase or decrease the fuel delivery as needed. Accurate fuel trim values require an accurate feedback signal from the Oxygen sensor, otherwise the engine computer has no way of knowing whether the fuel mixture is running rich or lean. When a cold engine is first started, it may take 10 to 30 seconds or more for the heaters inside the oxygen sensors to warms the sensors up to operating temperature. Until that point is reached and the fuel feedback control system goes into "closed loop", the fuel mixture is fixed at a predetermined value so no fuel trim adjustments are made. But once the Oxygen sensors are hot and the coolant temperature is high enough for the computer to go into closed loop, the computer
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starts to generate fuel trim values and make adjustments in the fuel mixture. When the engine is shut off, the fuel trim values are retained in the computer’s memory so the next time the vehicle is driven it can pick up where it left off. Erasing the computer’s memory with a scan tool or by disconnecting the battery or the PCM power supply to clear codes also wipes the fuel trim values, which means the computer has to start learning the fuel adjustments all over again the next time the engine runs.
How to Read Fuel Trim
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The fuel trim value is read by plugging a scan tool into the OBD II diagnostic connector located under the instrument panel (on the drivers side near the steering column). When the key is turned on, the scan tool will initialize and start to communicate with the vehicle’s onboard computer. Depending on the tool and the vehicle, it may be necessary to enter the vehicle year, make, model and engine VIN code before the scan tool can read the data. The engine must be started and running to read the fuel trim information. Depending on the scan tool and how its menu options are set up, you choose the option that allows you to read system live data. This will display a long list of sensor outputs and other readings called PIDs (Parameter IDs). On this list will be two fuel trim values for inline four and six cylinder engines, and four fuel trim values for V6 and V8 engines (one pair for each cylinder bank).
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There are two types of fuel trim values shown: Short Term Fuel Trim (STFT) is what the engine computer is doing to the fuel mixture right now. This value changes rapidly and can bounce around quite a bit depending on engine load, speed, temperature and other operating conditions). Values normally range from negative 10 percent to positive 10 percent, though the readings may jump as much as 25 percent or more in either direction. Long Term Fuel Trim (LTFT) is a longer term average of what the engine computer has been doing to balance the fuel mixture over a predetermined interval of time. This value is a more accurate indicator of how the fuel mixture is being corrected to compensate for changes in the air/fuel ratio that are occurring inside the engine. STFT B1 is Short Term Fuel Trim engine cylinder Bank 1 STFT B2 is Short Term Fuel Trim engine cylinder Bank 2 LTFT B1 is Long Term Fuel Trim engine cylinder Bank 1 LTFT B2 is Long Term Fuel Trim engine cylinder Bank 2 How do you know which cylinder bank is 1 or 2 on a V6 or V8 engine? Bank 1 will be the cylinder bank that has cylinder number one in the engine firing order. For more information on firing orders, see the following: Firing Orders (Chevy) Firing Orders (Chrysler) Firing Orders (Ford)
What Fuel Trim Values Mean POSITIVE fuel trim values mean the engine computer is adding fuel (increasing the pulse width or on-time of the fuel injectors) to add more fuel to the engine. In other words, it is attempting to RICHEN the fuel mixture because it thinks the engine’s air/fuel mixture is running too lean. NEGATIVE (-) fuel trim values mean the engine computer is subtracting fuel (decreasing the pulse width or on-time of the fuel injectors) to reduce the amount of fuel injected into the engine. This is done to LEAN out the fuel mixture to compensate for what it perceives as a rich running condition.
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Remember, all this is based on what the oxygen sensors are telling the engine computer. If the O2 sensors indicate LEAN, the computer adds fuel and generates a POSITIVE fuel trim value. If the O2 sensors are reading RICH, the computer compensates by subtracting fuel and generates a NEGATIVE fuel trim value. By reading the STFT and LTFT fuel trim values on a scan tool while your engine is running, you can tell if the air/fuel mixture is running rich (negative fuel trim percentages) or lean (positive fuel trim percentages).
What Fuel Trim Values Should Be Ideally, the STFT and LTFT should be within a few percentage points of zero when the engine is idling or being held at a steady RPM. Remember, STFT can bounce around quite a bit as when you suddenly snap open the throttle or decelerate. But LTFT can tell you if the average fuel/mixture is running rich or lean. Good LTFT values should be as close to zero as possible, though they can range from 5 to 8 percent depending on the condition of the engine. If the LTFT is getting up around 10 percent or higher, it usually indicates a problem that needs to be diagnosed. LTFT values that get up around 20 to 25 percent will usually set a P0171 or P0174 lean code. LTFT values that drop down to negative 20 to 25 will usually set a P0172 or P0175 rich code.
This scantool is displaying a STFT value of 25 percent. Normally that would indicate a problem, but in this case the engine is not running (Engine RPM is zero). As soon as the engine starts and goes into closed loop, the fuel trim readings will begin to change.
How Fuel, Ignition and Engine Problems Affect Fuel Trim Lean fuel mixtures are a more common problem than rich fuel mixtures, though either can happen depending on the cause. LEAN fuel mixtures will generate higher than normal POSITIVE fuel trim readings on your scan tool. RICH fuel mixtures will generate NEGATIVE fuel trim values. Some possible causes of LEAN fuel mixtures include: Air or vacuum leaks in the intake manifold, near the throttle body or at vacuum hose connections. Weak fuel pump that is not generating enough pressure or volume Fuel line restrictions (like a pinches hose or plugged filter) A weak fuel pressure regulator that is not maintaining adequate fuel pressure Air leaks in the PCV plumbing Dirty MAF (Mass Airflow) sensor that is under reading airflow into the engine Dirty or dead fuel injectors
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Ignition misfire (a fouled spark plug, weak ignition coil or bad plug wire that causes a misfire allows unburned oxygen to pass into the exhaust and fool the O2 sensors) Compression leaks (bad exhaust valve that allows unburned oxygen into exhaust and fools O2 sensors) Exhaust manifold crack or gasket leak (allows unburned air into exhaust and fools O2 sensors) Bad O2 sensor (signal shorted to ground so the sensor reads lean all the time) Some possible causes of RICH fuel mixtures include: Leaky fuel injector Excessive fuel pressure due to bad fuel pressure regulator or restricted fuel return line Extremely dirty air filter or restrictions in air intake system Exhaust restrictions (clogged converter, crushed exhaust pipe or plugged muffler) Bad O2 sensor (output shorted to voltage so it reads RICH all the time)
Using Fuel Trim to Diagnose Problems Use Fuel Trim to Diagnose Vacuum and Fuel Delivery Leaks. With the engine idling, look at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values. Normal range may be high as plus or minus 8, but closer to zero is best. If the numbers are +10 or higher for STFT and LTFT, your engine is running LEAN. Rev the engine to 1500 to 2000 RPM and hold it steady for half a minute or so. If the fuel trim numbers drops back down to a more normal reading, it confirms the engine has a vacuum leak at idle. This is because vacuum leaks have less of a leaning effect on the fuel mixture as engine speed and load increase. If the fuel trim readings do not change much, the lean fuel condition is more likely due to a fuel delivery problem (weak fuel pump, restricted fuel filter, dirty fuel injectors or a leaky fuel pressure regulator) than a vacuum leak. LTFT fuel trim readings that are trending high might also be the result of a slight ignition misfire that is not bad enough yet to set a misfire code but is bad enough to cause a drop in fuel economy. One or more fouled spark plugs that are misfiring occasionally, or a weak ignition coil or bad plug wire that is allowing some occasional misfires could be the cause. For more information on misfire diagnose, Click Here. You can use fuel trim to identify dirty fuel injectors. If the LTFT fuel trim readings are trending up (POSITIVE), it means the fuel feedback control system is compensating for an air/fuel mixture that is becoming progressively leaner over time. The most likely cause would be dirty fuel injectors. Fuel delivery can be restricted by the accumulation of varnish deposits inside the injector nozzles. The fix here is to clean the injectors. If the fuel trim values return to normal after the injectors have been cleaned, it verifies you have solved the problem. If the fuel trim values don't change after cleaning the injectors, the lean fuel condition may be due to low fuel pressure or air/vacuum leaks. You can use fuel trim readings to check the response of the oxygen sensors and engine computer to changes you make in the fuel mixture. While the engine is idling, temporarily disconnect a vacuum hose. You should see the STFT fuel trim readings jump immediately and go POSITIVE, and the LTFT should start to creep up in response to the artificial lean fuel mixture you have just created by disconnecting the vacuum hose. To test a rich response, you can feed some propane vapor from a small propane tank into the throttle body or a vacuum hose connection on the intake manifold. This time, you should see a drop in fuel trim readings, with STFT going NEGATIVE, and LTFT creeping downward in response to the rich fuel mixture. No change in fuel trim readings when you create an artificial lean or rich fuel mixture would tell you the engine computer is NOT operating in closes loop, or that the oxygen sensor(s) are not responding to changes in the fuel mixture. Got a Fuel Trim or Fuel Related Problem? Need Help Now? Click the Banner Below to Ask an Expert:
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Gasoline Direct Injection
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Gasoline Direct Injection (GDI) Copyright AA1Car.com
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Gasoline Direct Injection (GDI) is a type of fuel injection system that sprays gasoline directly into the combustion chamber. Like engines equipped with Multiport Fuel Injection (MFI) systems, there is a separate fuel injector for each of the engine's cylinders. But instead of mounting the injectors in the intake manifold so the injectors spray fuel into the intake ports in the cylinder head, the GDI injectors are mounted in the cylinder head and spray fuel directly into the combustion chamber instead of the intake port. The fuel bypasses the intake valves entirely and enters the cylinder as a high pressure mist. Fuel may be injected at any point during the intake stroke, or if the engine is running in low load ultra-lean mode, the fuel may not be injected until some point during the compression stroke. The air/fuel mixture is then compressed and ignited by a spark as the piston approaches top dead center. The exploding air/fuel mixture generates heat and pressure that pushes the piston down during the power stroke. The burnt exhaust gases are then pushed out of the cylinder during the exhaust stroke.
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High Pressure Fuel Injection Direct injection requires extremely high operating pressures (up to 2200 PSI) compared to conventional multiport fuel injection systems that typically require only 40 to 60 PSI. Direct injection requires more delivery pressure to overcome compression pressure inside the cylinder and to delivery a higher volume of fuel in a shorter period of time.
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Gasoline Direct Injection fuel rail for a V6. With ordinary MFI fuel injection, the fuel is sprayed into the intake port which is under vacuum. The fuel mist is then drawn into the combustion chamber along with the incoming air, mixed together during the compression stroke, and then ignited by the spark plug. With GDI, only air is drawn past the intake valves because the fuel is sprayed directly into the into the combustion chamber during the compression stroke. Some engines with direct gasoline injection do not have a conventional throttle because the throttle is not used to control engine speed and power. The engine computer does that by varying the time and amount of fuel that is injected into each cylinder. Eliminating the throttle means there is no restriction to incoming air and little or no vacuum in the intake manifold. This reduces the normal pumping loses caused by the throttle plates and intake vacuum for improved engine efficiency. As the piston comes up during the compression stroke, fuel may be injected into the cylinder at any point prior to ignition. The timing of the injection will depend on engine speed, load and operating conditions. In some situations (such as light cruise), fuel may not be injected until the piston has almost reached Top Dead Center on its compression stroke. Additional injection pulses of fuel may also be delivered once the initial mixture ignites to keep the flame burning during the power stroke.
Advantages of Gasoline Direct Injection Spraying fuel directly into the combustion chamber as compression is building, and during and after initial combustion allows the engine to make more power using less fuel. Engines with GDI can tolerate extremely lean fuel mixtures (up to 40:1) under light load and cruise conditions. The net result is typically 15 to 20 percent better fuel economy compared to multiport fuel injection. The ability to closely control the fuel mixture and give the engine just what it needs at just the right moment also means GDI engines can handle higher static compression ratios. The Buick 3.6L V6 has a compression ratio of 11.3 to one, which helps improve combustion efficiency and power. The Mazda Skyactiv-G 2.0L and 2.5L engines have a 14:1 compression ratio for even higher efficiency. GDI engines usually produce more horsepower than those with multiport injection systems.
Gasoline Direct fuel Injection Problems No new technology is trouble free and gasoline direct injection is no exception. Because fuel is injected directly into the combustion chamber rather than the intake port, the fuel provides little or no "cleaning effect" to keep carbon and soot from building up on the intake valves. As the miles add up, a layer of carbon deposits accumulates on the intake valves. As the deposits build up on the valve face, they may prevent the intake valves from sealing causing a compression leak, engine misfire and loss of power. Heavy carbon accumulations on the intake valves can also restrict airflow, hurt power at higher engine speeds and cause a drop in fuel economy and performance. Carbon deposits on the intake valves may also flake off and pass through the combustion chamber and into the exhaust. If the engine is equipped with a turbocharger, there is a chance the carbon could damage the turbine fins in the turbocharger. For more information, see Intake Valve Deposits in Gasoline Direct Injection Engines.
The soot buildup problem tends to be worse in direct injection engines that are used mostly for short trips. The intake valves never get hot enough to burn off the deposits. And if the valve guide seals allow too much oil to dribble down the valve stems, the carbon buildup goes even faster. The fix for dirty intake valves is to clean the valves with some type of chemical cleaner sprayed into the throttle body, intake manifold or directly into the intake ports. Another repair option in some cases is to remove the intake manifold and spray solvent directly into the intake ports in the cylinder head, or to blast clean the backside of the intake valves with a soft media such as walnut shells, baking soda or plastic beads. For extremely heavy carbon deposits, it may be necessary to remove the cylinder head to clean the valves. Another problem with gasoline direct injection is that like diesel injection, the fuel has less time to mix with the incoming air before it ignites. The stratified charge effect that direct injection produces also allows richer mixtures near the spark plug and injector, and leaner mixtures further away from the spark plug and injector. The result is that the combustion process can form larger particles of soot similar to that of untreated diesel exhaust. The size and quantity of the particles varies depending on the volatility of the fuel and other operating conditions. Current particulate emission regulations in the U.S. allow up to 10 mg/mile of particulates. But if future particulate emission regulations require lower levels, some type of exhaust after-treatment similar to that which is now being used on clean diesel applications may be required. Diesel engines have soot traps and urea injection systems for after-treatment.
Gasoline Direct Injection Applications Gasoline direct injection is used on a variety of late model engines: Audi, BMW, GM, Ford, Hyundai, Kia, Lexus, Mazda, MINI, Nissan, Porsche, VW and others. Some recent domestic applications include Ford Ecoboost engines (which are also turbocharged) in the 2010 Focus & Edge and 2011 Explorer, and the DI 3.6L V6 engine in the 2010 Buick LaCrosse and Enclave, 2010 Cadillac STS and CTS, 2010 Camaro V6, 2010 Chevy HHR SS, 2010 Chevy Traverse and GMC Acadia. The 2014 Corvette LT1 also has direct injection. By 2016, almost half of all new vehicles sold in the U.S are prediced to have gasoline direct injection engines.
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Shown above is a cutaway of the combustion chamber inside a Buick 3.6L V6 Direct Injection engine.
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More Fuel Injection Related Articles: Intake Valve Deposits in Gasoline Direct Injection Engines How Electronic Fuel Injection Works Fuel Injection Diagnostics Fuel Injection Problems Fuel Injection: Diagnosing Returnless EFI Fuel Injectors (cleaning) Fuel Injectors (troubleshooting) Got a Fuel Injection Problem or Question? Need Help Now? Click the Banner Below to Ask an Expert:
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Troubleshoot Fuel Injectors Copyright AA1Car Adapted from an article written by Larry Carley for Underhood Service magazine Clean fuel injectors are a must for peak engine performance, fuel economy and emissions. If the injectors are dirty and cannot deliver their normal dose of fuel, then performance, fuel economy and emissions are all going to suffer. Dirty injectors cannot flow as much fuel as clean ones, nor can they deliver the correct spray pattern that is so essential for clean, efficient combustion. The fuel feedback control system will compensate for the leaning effect once it is in closed loop, but it cannot correct the underlying condition that is causing the problem. The injectors need to be cleaned if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and higher hydrocarbon (HC) and carbon monoxide (CO) emissions. Lean misfire may also trigger a misfire code and turn on the Check Engine light on 1996 and newer vehicles with OBD II systems. The code often will be a P0300 random misfire code, or you may find one or more misfire codes for individual cylinders, depending on which injectors are most affected. Fuel Injector Clogging It does not take much of a restriction in an injector to lean out the fuel mixture. A restriction of only 8% to 10% in a single fuel injector can be enough to cause a misfire. When this occurs, unburned oxygen enters the exhaust and makes the O2 sensor read lean. On older multiport systems that fire the injectors simultaneously, the computer compensates by increasing the on-time of all the injectors, which can create an overly rich fuel condition in the other cylinders.
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In turbocharged engines, dirty injectors can have a dangerous leaning effect that may lead to engine-damaging detonation. When the engine is under boost and higher rpm, it needs all the fuel the injectors can deliver. If the injectors are dirty and cannot keep up with the engine's demands, the fuel mixture will lean out, causing detonation to occur. All vehicles are vulnerable to injector clogging, but the ones that are most vulnerable and most likely to experience such driveability and emissions problems are older ones with pintle-style multiport injectors. Later injector designs are more resistant to clogging. In the early pintle-style injectors, the nozzle shape and orifice size determine how much fuel flows through the injector and the shape of the spray pattern. Most pintle-style injectors are designed to produce a coneshaped spray pattern. But, if fuel deposits accumulate in the nozzle area, it can restrict fuel delivery and break up the spray pattern, causing a lean fuel condition and many of the problems just mentioned. Fuel Injector Deposits Where do the deposits come from? Mostly from the fuel itself. Gasoline is a mixture of many different hydrocarbons, including oilfins, which are heavy, waxy compounds. The heavier the hydrocarbon, the more energy it yields when it burns. When the engine is shut off, the injectors undergo heat soak. Fuel residue in the injector nozzles evaporates, leaving the waxy oilfins behind. Because the engine is off, there is no cooling airflow through the ports and no fuel flow through the injectors to wash it away, so heat bakes the oilfins into hard varnish deposits. Over time, these deposits can build up and clog the injectors. The formation of these deposits is a normal consequence of engine operation, so detergents are added to gasoline to help keep the injectors clean. But if a vehicle is used primarily for short-trip driving, the deposits may build up faster than the detergents can wash them away. On four-cylinder engines, the #2 and #3 injectors are in the hottest location and tend to clog up faster than the end injectors on cylinders #1 and #4. The same applies to the injectors in the middle cylinders in six- and eight-cylinder engines. The hotter the location, the more vulnerable the injector is to clogging from heat soak. Throttle body injectors are less vulnerable to heat soak because of their location high above the intake manifold plenum. Detergents In Gasoline To save a few pennies per gallon and to increase the competitive and/or profit margin of gasoline, some suppliers have cut back on the amount of detergent they add to their fuel or have switched to cheaper and less-effective additives. Commonly used deposit-control additives include polysibutylamine, polyisbutylene succinimide and polyisobutylene phenylamine. But these same additives also can build up on intake valve stems causing them to stick. To prevent this from happening, additional additives called fluidizers also must be added to the fuel. But, over time, these can contribute to the formation of combustion chamber deposits that raise compression and the engine's octane requirements. Dirty injectors lean out the fuel mixture and contribute to lean misfire, hesitation and even detonation. Cleaning should restore like-new performance. One of the best additives is polyetheramine. It keeps injectors, valves and combustion chambers clean without the help of any additional fluidizers - but it costs more than twice as much as the other commonly used additives. How much additive does it take to provide an adequate level of protection? Industry sources say the recommended level is about 1,000 parts per million (ppm) of dispersant-detergent in the fuel - which costs the gasoline supplier less than a penny a gallon. Even so, as much as 85% of the gasoline that is being sold contains only one-tenth of the recommended dosage, or only 100 ppm of additive. Consequently, using cheap gas contributes to the formation of injector deposits. Fuel Injector Cleaning
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The benefits realized by injector cleaning obviously will vary depending on the condition of the injectors prior to cleaning and how badly they were clogged. Injectors that are really dirty should show more of a noticeable improvement in performance than ones that have only a light accumulation of deposits. Either way, performance, fuel economy and emissions should all be better after a cleaning. Most high-mileage engines, as well as engines that are used mostly for short-trip, stop-and-go driving, are the most likely prospects for injector cleaning. Some experts recommend cleaning the injectors every 25,000 to 30,000 miles to keep them flowing at peak efficiency. More Cleaning Opportunities Another component that also may need to be cleaned to remove fuel varnish is the throttle body. Fuel vapor rising up through the intake manifold can accumulate and vaporize around the throttle plate and air bypass circuits, causing a change in the idle air/fuel mixture. Sometimes you can see the deposits, and sometimes you cannot. Either way, cleaning the throttle body and intake tract also may be necessary to fully restore engine performance, idle quality and emissions. An aerosol cleaning solvent works well here. The intake valves and combustion chambers also should be cleaned when you do the injectors to remove deposits that may also be contributing to driveability and emissions problems. Deposits on the backs of intake valves can act like a sponge and absorb fuel, causing a momentary hesitation when the throttle is suddenly opened. Combustion chamber deposits increase compression and the risk of engine-damaging detonation (spark knock). Engines that burn oil typically will have heavy intake valve and combustion chamber deposits that do not respond well to normal levels of detergent in gasoline. Additional cleaner is needed, which can be added to the fuel tank or run directly through the injectors. To remove carbon deposits from the intake valves and combustion chambers, use a top cleaner type of product and follow the instructions, or use equipment that is designed to clean the upper engine. Direct injection fuel injectors have very precise spray patterns and are even more sensitive to deposits than regular injectors. Observing the spray patterns of a set of injectors can show you at a glance if any are misshapen or contain streamers of unvaporized liquid. Note: Some experts recommend replacing the spark plugs after doing an on-car injection cleaning or decarbon treatment. The residue that is loosened and washed away by the solvent may increase the risk of plug fouling. Changing the oil and filter is also a good idea following a cylinder decarbon treatment because some of the solvent will get past the rings and end up in the crankcase. Fuel Injector Cleaning Options Should you clean the injectors in place or remove them and use some type of injector cleaning machine? It depends. The easiest route is to clean the injectors in place because you do not have to remove them (which can be a real chore on some import engines). Running cleaner through the injectors while the engine is running also removes many of the deposits on the valves and inside the combustion chambers. This eliminates the need for an extra cleaning step if the engine is full of carbon deposits. The job takes only 10 to 15 minutes, and you can usually tell right away if the treatment addressed the problem (engine runs smoother, idle misfire gone, etc.). When doing the cleaning procedure itself, you must use pressurized equipment to feed the solvent directly into the fuel rail while the engine is running. This means you either have to disable the fuel pump and plug the fuel return line, or install a Utube so the fuel will recirculate right back to the tank. Disabling the fuel pump can set a fault code on some cars, requiring you to clear the code after the job is done. Easy as it is, there are some limitations with on-car injector cleaning. One is that badly clogged injectors may not pass enough solvent during a normal cleaning cycle to be thoroughly cleaned. Some baked-on deposits can be very difficult to remove, requiring you to prolong or repeat the cleaning process. And if on-car cleaning does not work? You will have to remove the injectors and try to clean them on an injector cleaning machine - or replace them.
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Another limitation with on-car injector cleaning is that you may have to do some additional tests to confirm that the injectors responded well enough to your cleaning efforts. A test drive may be needed to see if the driveability symptoms have been eliminated, or you may have to check emissions to make sure HC and CO levels are back to normal. A power balance test is another way to confirm engine performance and check for weak cylinders (there should be less than a 10% power variation between cylinders). An injector pressure drop test will tell you if the injectors are flowing evenly or not. There may be some risk to the vehicle's fuel system when using concentrated solvent to clean the injectors in place. Most equipment suppliers say to disconnect and plug the fuel return line so that solvent does not circulate back to the fuel tank. Strong solvents may attack rubber and plastic components in the fuel pump, regulator and fuel lines, creating additional problems that you don't want. Be Cautious During Cleaning On-car injector cleaning also involves some risk to the person who is performing the service. You have to disconnect pressurized fuel lines, make sure there are no fuel leaks, and feed high-pressure solvent (which is just as flammable as gasoline) into the engine while the engine is running. Safety precautions should always include eye protection, making sure there are no open sources of ignition (sparks) nearby, and avoiding direct exposure with the cleaning solvent. Clean Fuel Injectrors Off Car Injectors that are really dirty may not respond well to on-car cleaning. You may have to use a more powerful solvent and/or longer cycle time to loosen the baked-on deposits. That is where an off-car injector cleaning machine really pays for itself. Off-car injector cleaning is a more expensive service because of the labor involved to remove the injectors (which can be considerable on some applications), and it requires special equipment that can cost anywhere from $4,000 to $8,300. Many shops charge between $25 and $35 per injector for off-car cleaning - which makes it more costly to the customer than on-car cleaning. But it also can save customers a lot of money because off-car cleaning is a lot cheaper than replacing the injectors with new ones (which can cost hundreds of dollars!). Off-car injector cleaning can often restore dirty injectors that fail to respond to on-car cleaning. That is why some shops do only off-car cleaning. They don't want to have to clean the injectors twice. Off-car cleaning takes more time (typically 30 to 45 minutes after the injectors have been removed), and most machines have an ultrasonic bath that can be used to soak badly clogged injectors. Some machines also reverse-flush the injectors, which provides an added measure of cleaning. Another reason for using off-car cleaning equipment is that the injectors can be flow-tested after they have been cleaned to verify their performance. The injectors typically are mounted on a test manifold and energized to spray solvent into clear graduated cylinders. By comparing the volume of fuel delivered, it is easy to see if all the injectors are flowing evenly. As a rule, you should see less than 5% to 7% variation between injectors (some performance engine builders aim for 1% or less variation between injectors!). If an injector is not passing as much liquid as its companions, you can subject it to more cleaning. And, if it fails to respond to additional cleaning, there is no guesswork about which injector needs to be replaced. Perform a Flow Test Flow-testing also allows you to compare the actual flow rate of each injector to factory specifications. If the flow is within specifications, you know the injector should perform properly when it is reinstalled back in the engine. Flow-testing also is a good way to make sure the injectors are the right ones for the engine (one or more injectors may have been previously replaced by someone else). A flow test on the cleaning equipment allows you to see each injector spray pattern. If you see a normal, cone-shaped mist, you know the injector is flowing properly. If you see streamers of unvaporized liquid in the spray pattern, you know additional cleaning is needed or the injector needs to be replaced. Injector cleaning will be an ongoing need as long as engines are equipped with fuel injectors. Even the new generation of direct injection gasoline engines that are now being built are vulnerable to fuel deposits. So be on the alert for the symptoms of dirty injectors and do not hesitate to have the injectors cleaned for preventive maintenance.
Fuel Trim Diagnostics To maintain the correct air/fuel mixture, the PCM adjusts Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Both of these values can be read on a scan tool that can display OBD II system data, and may be used to diagnose fuel-related problems.
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Normal range for both STFT and LTFT is typically plus or minus 8. If the numbers are +10 or higher for STFT and LTFT, the engine is running LEAN (not enough fuel). If the values for both STFT and LTFT are both minus 10 or more, the engine is running RICH (too much fuel). Vacuum leaks can create a lean-running engine that requires extra fuel to balance the fuel mixture. If you rev the engine to 1500 to 2000 rpm and hold it for a minute or so, and the STFT value drops back down to a more normal reading, it confirms the engine has a vacuum leak at idle. If the STFT value does not change much, the lean fuel condition is more likely a fuel delivery problem (weak fuel pump, restricted fuel filter, dirty fuel injectors or a leaky fuel pressure regulator) than a vacuum leak. For more information about using fuel trim to diagnose a lean fuel condition, read this article on Fuel Trim by Wells Manufacturing (PDF file, requires Adobe Acrobat to read). Share
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Diagnose Electronic Fuel Injection Copyright AA1Car.com Adapted from an article written by Larry Carley for Underhood Service magazine
Electronic fuel injection is a great means of delivering fuel to an engine. With multiport systems, each cylinder receives its own dose of fuel, and with sequential controls, the air/fuel ratio for each cylinder can be quickly changed to keep in step with changes in engine load. EFI also improves cold starting, reduces emissions, improves fuel economy and performance. But sometimes things go amiss. Fuel injection problems encompass everything from hard starting, stalling and misfiring to hesitation, surging and no-starts. Dirty injectors, for example, will restrict the amount of fuel that is sprayed into the engine with every pulse of the injector resulting in a leaner-than-normal fuel mixture. This, in turn, can cause lean misfire, hesitation, poor performance and an increase in hydrocarbon (HC) emissions. Because EFI is part of the powertrain control module's feedback control loop, problems with the coolant sensor or oxygen sensor also can affect fuel delivery. A coolant sensor that always reads cold will prevent the engine from going into closed loop resulting in a rich fuel mixture and poor fuel economy. A dead oxygen sensor can have the same effect. So too, can a contaminated or sluggish O2 sensor. The PCM also relies on inputs from the throttle position sensor, airflow sensor (if one is used), manifold absolute pressure
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(MAP) sensor and intake air temperature sensors to adjust the fuel mixture. Most sequential injection systems use the signal from the camshaft or crankshaft position sensor to trigger and sync the injector pulses. Problems in any of these sensor circuits also can affect fuel delivery. Most PCMs have an internal driver circuit for grounding (or in some cases energizing) the injectors. Problems here can disable one or more injectors depending on how the system is wired. In some cases, a shorted injector will kill the driver circuit in the PCM. And don't forget the power relay that supplies voltage to the injectors. If this relay dies, it will disable all of the injectors. There's also the components in the fuel system itself: the fuel pump, pump relay, fuel filter, fuel lines, pressure regulator and injectors. Problems with any of these components may prevent fuel from reaching the engine or reaching it at the correct pressure. The point here is a lot of things can affect the operation of the fuel delivery system. The challenge is to figure out what is causing the problem without wasting a lot of time chasing dead ends. We don't have the space to explore every possibility, so we'll focus on the main components in the fuel system itself. Cranks But Won't Start Where do you begin your diagnosis if you have an engine that cranks but won't start? One of the first things you should do is check for spark. Got spark? What about compression? If the engine has a belt-driven cam, make sure the belt has not failed. Also, check for any loose hoses that might be creating a huge vacuum leak. If ignition and compression are both OK, that leaves fuel as the obvious culprit. Now the question is, what is wrong with the fuel delivery system? The most likely causes are: 1. A dead fuel pump (could be the pump, pump relay or wiring circuit); 2. A plugged fuel filter; 3. Low fuel pressure (weak pump or restricted line); or 4. No pulse signal to injectors (bad injector relay or PCM driver circuit). One of the first things to check is the fuel pump. Does the pump run when the engine is cranking? The pump should make a little noise. No noise would tell you the pump is not spinning. On most vehicles the pump is energized by the PCM via a relay. The pump circuit also may be wired though an oil pressure switch and/or an inertia safety switch that kills the pump in case of an accident. Refer to the wiring diagram to find out what is involved before jumping to any conclusions. Other electrical problems that can affect the pump include low voltage in the pump's power supply circuit or high resistance in the pump's ground connection. Either may prevent the pump from running or spinning fast enough to generate normal fuel pressure. Fuel Pressure Checks Depending on the application, the fuel system may require anywhere from 30 to 80 psi of fuel pressure to start and run. Pressure specifications will vary according to the type of fuel injection system on the engine as well as the performance, fuel economy and emission requirements of that particular model year vehicle. There are no rules of thumb. Every application is different, so always look up the pressure specs when troubleshooting fuel-related performance problems. When there is too much fuel pressure, the engine runs rich. This causes an increase in fuel consumption and carbon monoxide (CO) emissions. An engine that is running really rich also may experience a rough idle, surging and possibly even carbon-fouled spark plugs. When there is not enough fuel pressure, the engine may not start. Or if it does, it may idle roughly and run poorly. Low fuel pressure creates a lean fuel condition that can cause lean misfire, hesitation, rough idle, hesitation and misfire on acceleration. To check fuel pressure, you need a gauge and a place to attach it. There are a number of different checks that can be made, including static or rest pressure (key on, engine off), residual fuel pressure, running pressure, maximum or "dead head" pressure and volume of fuel delivered. The fuel pressure regulator also should be tested, and a fuel pressure drop test performed to check for dirty fuel injectors.
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Different vehicle manufacturers recommend different test procedures. On many European EFI systems, the OEMs recommend using a static pressure test with the engine and ignition off. This is done by bypassing the fuel pump relay and energizing the pump directly. Most domestic and Asian vehicle manufacturers, on the other hand, provide a test fitting on the fuel rail so pressure can be checked with the engine running. If you are working on a vehicle that does not have a pressure test fitting, you will have to tee a pressure gauge into the fuel line just ahead of the injector fuel rail. Caution: Before hook ing up your pressure gauge, relieve all pressure in the fuel system. Static Fuel Pressure Test With the key on, engine off (or with the fuel pump energized), fuel pressure should come up quickly and hold steady at a fixed value. Compare the pressure reading to specifications. If you get no pressure reading, check for voltage at the pump. If there is voltage but the pump is not running, you have found the problem: a bad fuel pump. If you do get a pressure reading but the reading is lower than normal, the cause may be a weak pump, a blockage in the fuel line, filter or tank inlet sock, or a faulty pressure regulator. Also, low voltage at the pump may prevent it from spinning fast enough to build up normal pressure. Check the voltage at the pump. If OK, check the fuel filter and lines for obstructions and the operation of the fuel pressure regulator before you condemn the pump. Residual Fuel Pressure Test When the pump is turned off or stops running, the system should hold residual pressure for several minutes (look up the specs to see how much pressure drop is allowed over a given period of time). If pressure drops quickly, the vehicle may have a leaky fuel line, a leaky fuel pump check valve, a leaky fuel pressure regulator or one or more leaky fuel injectors. Low residual fuel pressure can cause hard starting and vapor lock during hot weather. Running Fuel Pressure Test With the engine idling, compare the gauge reading to specifications. Fuel pressure should be within the acceptable range given by the vehicle manufacturer. If low, the problem may be a weak pump, low voltage to the pump, a clogged fuel filter, line or inlet sock inside the fuel tank, a bad pressure regulator, or nearly empty fuel tank. Dead Head Pressure This checks the maximum output pressure of the fuel pump. With the return line pinched shut, the pump should produce two times its normal operating pressure at idle. If the pressure rating does not go up with the return line blocked, the pump may not be able to deliver enough fuel at higher engine speeds. Possible causes include a worn pump, low voltage at the pump, a plugged fuel filter or inlet sock in the tank, an obstructed fuel line or almost empty fuel tank. Fuel Volume Test A fuel pump that delivers normal pressure may still cause driveability problems if it can't deliver enough fuel volume to meet the engine's needs. A fuel volume test may therefore be the best way to evaluate the pump's condition. A fuel volume test measures the volume of fuel delivered over a specified interval. This test can be done by connecting a fuel flow gauge into the fuel supply line, or by disconnecting the fuel return line from the fuel pressure regulator and connecting a hose from the regulator to a large container. Caution: Make sure there are no open sparks or flames nearby while doing this test! With the engine off, energize the pump and measure the volume of fuel delivered during the specified interval of time. As a rule, a good pump should deliver about 3/4 to one quart of fuel in 30 seconds. Causes of low fuel volume delivered include a worn fuel pump, a plugged fuel filter or inlet sock in the tank, obstructed fuel line or nearly empty tank. Don't forget that low voltage at the pump can also prevent it from running fast enough to generate adequate fuel flow. The pump's supply voltage should be within half a volt of normal system voltage. If it is low, check the wiring connectors, relay and ground. Fuel Pressure Regulator Test This test checks the operation of the fuel pressure regulator to make sure it changes line pressure in response to changes in engine vacuum. This is necessary to maintain the proper operating pressure behind the injectors and to compensate for changes in engine load. http://www.aa1car.com/library/2003/us60324.htm
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With the engine running, disconnect the vacuum hose from the pressure regulator. As a rule, fuel system pressure should increase 8 to 10 psi with the line disconnected. No change would indicate a faulty pressure regulator, or a leaky or plugged vacuum line. If the diaphragm inside the regulator is leaking, engine vacuum will suck raw fuel into the intake manifold through the vacuum hose (look for fuel inside the hose). Fuel Pressure Drop Test This test measures the drop in static system fuel pressure when each injector is energized. The amount of pressure drop for each injector is then compared to see if the injectors are dirty and need to be cleaned or replaced. This test requires an "injector pulser" tool to energize the injectors. To perform this test, turn the key on or energize the fuel pump for a few seconds to build up static pressure in the fuel system. Then turn the key off, pulse one injector for the specified time and note the pressure drop for that injector. Turn the key back on to rebuild static pressure and repeat the test for each of the remaining injectors. An injector that is pulsed 100 times for five milliseconds should produce a minimum pressure drop of about 1 to 3 psi, and no more than 5 to 7 psi, depending on the application. The difference in pressure drop between all the injectors should be 2 psi or less. If you see more than 3 psi difference between the highest and lowest readings, the injectors are dirty and need to be cleaned or replaced. If you see no pressure drop when an injector is energized, the injector is clogged or defective and needs to be replaced. If the pressure gauge needle bounces, the injector is sticking. After cleaning, repeat the test to see if cleaning did the trick. All injectors should show about the same amount of pressure drop (less than 2 psi difference) and no more than 7 psi drop at 100 pulses for 5 milliseconds. If there is no change in the readings or the drop exceeds these limits, the injector(s) need to be replaced. Scope Tests By connecting a Low Amps probe to the fuel pump's voltage supply wire, you can create a scope waveform that will reveal internal wear in the brushes and commutator that may not show up in a traditional pressure or volume test. Observing the waveform will tell you if the pump's amp draw is normal for the application or is high or low, and if the pump is operating at normal speed or is running slow. Problems such as a bad spot on a commutator or a short or open in the armature also will be obvious in the waveform. A "good" electric fuel pump waveform will generally seesaw back and forth with relative consistency and minimal variation between the highs and lows. A "bad" waveform will show large or irregular drops in the pattern, with large differences between the highs and lows. Pump Replacement If you have diagnosed a bad fuel pump and replacement is needed, be sure to inspect the inside of the fuel tank. The presence of rust or debris in the pump's pickup screen would tell you the tank needs to be cleaned or replaced. When replacing an in-tank pump, always disconnect the battery to prevent any unwanted sparks. Then drain the tank before removing the tank straps and opening the pump's retaining collar. When installing the new pump, always replace the in-tank pickup screen and use a new O-ring for the sealing collar.
Fuel Trim Diagnostics To maintain the correct air/fuel mixture, the PCM adjusts Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Both of these values can be read on a scan tool that can display OBD II system data, and may be used to diagnose fuel-related problems. Normal range for both STFT and LTFT is typically plus or minus 8. If the numbers are +10 or higher for STFT and LTFT, the engine is running LEAN (not enough fuel). If the values for both STFT and LTFT are both minus 10 or more, the engine is running RICH (too much fuel).
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Diagnose Electronic Fuel Injection
For more information on this subject, see What Is Fuel Trim? Vacuum leaks can create a lean-running engine that requires extra fuel to balance the fuel mixture. If you rev the engine to 1500 to 2000 rpm and hold it for a minute or so, and the STFT value drops back down to a more normal reading, it confirms the engine has a vacuum leak at idle. If the STFT value does not change much, the lean fuel condition is more likely a fuel delivery problem (weak fuel pump, restricted fuel filter, dirty fuel injectors or a leaky fuel pressure regulator) than a vacuum leak. For more information about using fuel trim to diagnose a lean fuel condition, read this article on Fuel Trim by Wells Manufacturing (PDF file, requires Adobe Acrobat to read).
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More Fuel Injection Articles: How Electronic Fuel Injection Works Gasoline Direct Injection (GDI) Toyota Fuel Injection Troubleshoot Fuel Injectors Troubleshooting & Cleaning Fuel Injectors What Is Fuel Trim? Fuel Filters Troubleshoot Idle Surge Fuel System Diagnostics: Finding the Best Approach Diagnosing Returnless Electronic Fuel Injection Systems Electric Fuel Pumps Fuel Pump Diagnosis How To Replace an In-Tank Electric Fuel Pump Bad Gasoline Can Cause Performance Problems Bad Gas Update 2006 Fuel Octane Ratings & Recommendations
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Fuel System Diagnostics
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Fuel System Diagnostics Copyright AA1Car Adapted from an article written by Larry Carley for Underhood Service magazine With today's computerized engine controls and electronic fuel injection, it's hard to separate the fuel system from other systems when it comes to driveability and emissions diagnostics. Symptoms such as hard starting, stalling, hesitation, loss of power, poor fuel economy, rough idle, misfiring and elevated emissions can be caused by any number of things. So your job is to zero in on the most likely causes using the quickest and most effective procedures at your disposal. Sometimes this means ruling out other possibilities first, such as ignition or compression problems. Once these have been eliminated, you can focus on the fuel system and try to isolate the problem using the appropriate tests. Before we go any further, let's define which parts we are talking about. The fuel system includes everything from the fuel filler cap, fuel tank, fuel pump, pump relay, fuel lines and filter to the fuel injectors, pressure regulator, fuel rail and throttle body. But our list may also include other parts and systems that influence or control the operation of the fuel system such as the PCM, oxygen sensor, coolant sensor, MAP sensor, throttle position sensor and airflow sensor (if one is used). There is also the idle speed control system, and the evaporative emissions system that captures and manages fuel vapors. We also have to include the fuel itself because "bad gas" that has been contaminated with water or higher-than-normal amounts of alcohol additives is still an often-overlooked cause of common driveability problems.
Basic Causes of Fuel Injection Problems Fuel-related driveability and emission problems can be lumped into one of three basic categories: Code but no obvious driveability or emissions problem; Code and a driveability or emissions problem; or No code but a driveability or emissions problem. The first two are usually easier to diagnose because you at least have a starting point (the fault code). The last one (no code) is the most challenging because you have only the symptom(s). If the Check Engine light is on, you know the computer has detected something wrong and has logged one or more diagnostic trouble codes that correspond to the fault(s). When you hook up your scan tool, you know you are going to find some kind of information that should get you headed in the right diagnostic direction.
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Without getting too philosophical, we all know that some codes are more helpful than others. It depends on the code, the conditions that are required to set it and the diagnostic procedures that follow it. A code that indicates a particular sensor is reading out of range is usually a good indication that there is a problem in the sensor circuit. But if that code is accompanied by other codes, it often indicates an operating condition that is throwing the sensors off. When there is more than one code, it sometimes makes matters worse because you may not be sure where to start. Should you go in numerical sequence, or should you step back and try to figure out what kind of condition would cause multiple codes to be set?
What Might Be Causing Your Fuel Injection Problem?
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Let's assume you have a late-model OBD II car with a four-cylinder engine. The Check Engine light is on and the engine idles a little rough and has some hesitation. You hook up your scan tool and find a P0131 code that indicates the O2 sensor is reading low (lean) and a P0300 code for a random misfire. Is the O2 sensor bad or is it something else?
The problem might be a faulty O2 sensor, but more likely causes include a vacuum leak, low fuel pressure or dirty injectors that are leaning out the fuel mixture, causing the engine to run poorly and misfire. It might even be bad gas. What you do next will depend on the type of diagnostic equipment you have and what you think is the most likely cause. You might begin your investigation by inspecting the intake manifold and vacuum hoses for obvious leaks. Finding none, you might hook up a vacuum gauge to see if intake vacuum readings are steady at idle and within normal range. A low reading could indicate a vacuum leak somewhere or possibly a leaking EGR valve. Further investigation would be needed to determine the cause if the readings are abnormal. Next, you might use your scan tool, a DVOM or scope to look at O2 sensor performance. If the O2 sensor responds normally when you temporarily enrichen the fuel mixture by feeding some propane into the engine, or lean the mixture by disconnecting a vacuum line, you can probably assume the O2 sensor is OK. And if the engine control system is in closed loop (check loop status) and changes the injector dwell in response to changes in the O2 sensor reading, you can assume the feedback fuel control loop is doing its job, too. Next, you might connect a pressure gauge to the fuel rail and check fuel pressure and the operation of the fuel pressure regulator. Does the pressure change when you disconnect the regulator vacuum line or pinch off the return hose? Low pressure readings would lead you to suspect a weak pump, while no change in the pressure readings when playing with the regulator would point toward a faulty regulator. If fuel pressure is normal, you might look at the injector patterns on your scope. Does the dwell change when you goose the throttle or make the mixture go rich or lean? You might also use your scope to look at the engine's secondary ignition pattern. When one or more (but not all) of the spark firing lines slope up to the right and firing time shortens, it indicates a lean fuel condition in the affected cylinders. A rich mixture is more conductive than a lean one, and requires less voltage to sustain a spark. On a fuel-injected engine, this could be a symptom of a dirty, clogged or inoperative fuel injector. The premature snuffing out of the spark can also be caused by poor cylinder breathing due to a rounded cam lobe or a leaky exhaust valve. A lean fuel mixture will also cause the firing KV to be higher than normal. If the fuel mixture is running rich because the O2 sensor is dead or the feedback control system is stuck in open loop, the firing line portion of the secondary ignition pattern will show hairlike extensions hanging from the spark line. This is caused by the increased conductivity of the rich mixture. The KV firing voltages will also be lower than normal with a longer-than-normal
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Fuel System Diagnostics
spark duration. Another alternative would be to hook up an exhaust emissions analyzer to look at carbon monoxide (CO) and hydrocarbons (HC). Higher-than-normal CO would tell you the mixture is running rich, while elevated HC would tell you there is a misfire or compression problem (lean misfire, ignition misfire or a burned exhaust valve). If you use the exhaust analyzer in conjunction with a power balance test, you can see if the HC readings change when each injector is shorted out. No change in HC would indicate a bad injector. If the change in HC is noticeably less on one cylinder than the others, it would tell you that injector is probably restricted and needs to be cleaned or replaced. If you suspect dirty injectors, your next step might be to clean the injectors on the car. Or, if you have an off-car injector cleaner, you might pull the injectors, flow test them on the bench and clean them to see if normal performance can be restored (if not then you will have to replace the injectors). According to some experts, a difference of more than 7 to 10% in flow rates between individual injectors on a multiport system is enough to cause noticeable driveability problems. Some cylinders will run too rich while others will run too lean. Ideally, all the injectors should flow within 3 to 5% of one another. If they don't, the computer will compensate for the leanest injector, forcing all the others to run rich.
When There Is No Fault Code
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No-code driveability and emission problems are the ones everybody hates, especially when the symptoms are intermittent. In such situations, you have to go look at the symptom(s) and make some educated guesses as to what to look at first. As before, how you approach a no-code problem will depend on what you have in your diagnostic arsenal. If you have an emissions analyzer, you might look at exhaust gases first. If you have a scope, you might examine sensor, injector, ignition or even the fuel pump waveforms. Since most technicians today own some type of scan tool, checking system data is as good a place as any to start, even when there is no code. One of the first things you should check is loop status. The fuel system cannot deliver the proper fuel mixture if is stuck in open loop. If the engine fails to go into closed loop after it has warmed up or been driven, it may have a faulty coolant sensor or an open thermostat. The next logical step would be to look at the coolant sensor's output to see if it is reading normally or if its resistance changes as the engine warms up. No change in resistance or a reading that is out of range would tell you the coolant sensor is bad. To check the thermostat, you could use an infrared thermometer to measure coolant temperature at the thermostat outlet after the engine has warmed up. If low, the thermostat may be open, missing or the wrong temperature rating for the engine.
You can also look at short-term and long-term fuel trim to see if the engine is running rich or lean. If the system is going into closed loop, look at the TPS and MAP inputs to make sure they are changing when the throttle position changes. For more information about feedback fuel control, see What Is Fuel Trim?
Expert Troubleshooting At the last International Automotive Technicians Network (iATN) convention in Dearborn, MI, a roomful of top technicians from all over the country was challenged to correctly diagnose several real-world driveability problems. They were given a description of some vehicles and their symptoms, then allowed to view actual test data that was taken from the vehicles using a variety of different diagnostic tests and equipment.
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Fuel System Diagnostics
The challenge was to figure out which diagnostic tests and equipment would provide the most useful information, and to then analyze this information to come up with a diagnosis. It proved to be a difficult task because opinions differed as to what data should be looked at first, and what the data actually meant. Some people resorted to making wild guesses in an attempt to solve the problems. One example that stumped a lot of technicians was a car that would start and run fine when cold, but had a hot-start problem. It would crank but not start. It had fuel, spark and compression. Fuel pressure and vacuum readings were normal. Coil resistance, spark plugs and wires were all within specifications. The hot-start problem turned out to be a bad coolant sensor. The sensor was preventing the fuel system from going into closed loop, which created a rich mixture that flooded the engine when a hot start was attempted. The diagnostic approach for solving a no-start condition that evolved from this was to: 1. Check for spark to rule out ignition problems. 2. Check for fuel to rule out an empty tank, dead fuel pump or plugged fuel line. 3. Check compression to rule out a broken cam, timing chain or OHC timing belt. If all of the above are OK, remove and examine a spark plug. If the plugs are wet, it would tell you the engine is flooded due to too much fuel. The underlying cause would be a defective coolant sensor or leaky injector(s). Another approach when confronted with a no-start condition is to check cranking vacuum. It should usually be at least 3". If lower than this, there is a compression problem. Also, look at the amount of HC in the exhaust. If you see at least 7,500 ppm of HC, there should be enough fuel to start. If the HC reading is below 7,500 ppm, there is not enough fuel. On many vehicles, a no-start can occur if the oil pressure switch is bad. The oil pressure switch is wired into the fuel pump relay circuit to cut voltage if oil pressure is lost. This is to prevent fuel from spraying out of a ruptured fuel line in the event of an accident. Some vehicles also have an inertia crash switch hidden somewhere in the bodywork (look in the trunk, under the back seat or inside the rear seat side panels) to cut off fuel in case of an accident. An inertia switch can be reset by pressing its reset button. Hard starting on some older fuel injected systems can be caused by a faulty cold start injector. A timed relay energizes the injector when the engine is cranked to provide extra fuel. Most problems here can be traced to electrical faults in the control relay or wiring. Use a test light to check the cold-start injector when the engine is cranked. No voltage means the relay (or its fuse) is bad.
Leaky Fuel Injectors Wear in the injector orifice and/or accumulated deposits can sometimes prevent the pintle valve inside an injector from seating, allowing fuel to dribble out the nozzle. The extra fuel causes a rich fuel condition, which can foul spark plugs, increase emissions and cause a rough idle. A carbon-fouled spark plug in one cylinder of a multi-port EFI engine usually indicates a leaky injector. If cleaning fails to eliminate the leak (which it can if dirt or varnish are responsible), replacement will be necessary.
Idle Problems Idle problems can usually be traced to an air or vacuum leak, or in some cases, a faulty idle air bypass control motor or plugged idle bypass circuit. Leaks allow "unmetered" air into the engine and lean out the fuel mixture. The computer compensates by richening the mixture and closing off the idle bypass circuit. One of the symptoms of a vacuum leak, therefore, is a bypass motor run completely shut. You can use your scan tool to check for a vacuum leak by looking at the fuel trim values. If the engine has a vacuum leak, the fuel trim values will usually be higher than normal (positive) when the engine is idling, but will drop back more towards normal when engine speed is increased. This is because a vacuum leak has less affect on the fuel mixture at higher engine speeds than at idle.
Plugged Fuel Filter A plugged filter can restrict the flow of fuel and starve the engine, causing a loss of power at high speed, a lean fuel mixture
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or a stalling/no-start condition if the blockage is severe. The easiest way to check the filter is to remove it and attempt to blow air through it. If the filter is plugged with rust or sediment, it is probably a good idea to drain and clean the fuel tank to prevent a repeat failure. If the tank is badly corroded inside, replacing the fuel tank would be recommended. A restricted filter sock on the fuel pump pickup can cause similar symptoms, too. So, if the filter appears to be OK or replacing it fails to solve the problem, it may be necessary to drop the tank, remove the pump and inspect, clean or replace the filter sock. Got a Fuel Injection Problem? Need Help Now? Click the Banner Below to Ask an Expert:
More Fuel Injection Articles: How Electronic Fuel Injection Works Gasoline Direct Injection (GDI) What Is Fuel Trim? Toyota Fuel Injection Troubleshooting Electronic Fuel Injection & Fuel Pump Diagnosis Electric Fuel Pumps Fuel Pump Diagnosis How To Replace an In-Tank Electric Fuel Pump Troubleshooting Fuel Gauges Fuel Filters Car Won't Start (Possible Causes & Quick Checks) Troubleshooting Fuel Injectors Troubleshooting Hesitation Problems Diagnosing Returnless Electronic Fuel Injection Systems Troubleshooting & Cleaning Fuel Injectors Bad Gasoline Can Cause Performance Problems Bad Gas Update 2006
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Fuel Injection Electric Fuel Pump Diagnostic Guide Use these Diagnostic Charts to quickly and accurately determine the exact cause of electric fuel system malfunction. The fuel pump is only one of many possible factors that must be evaluated before the proper repairs can be performed.
CHART 1 Is there gas in the tank? (Add 2 gallons)
Vehicle runs
Vehicle does not run
Vehicle was out of gas pump is good
Energize pump circuit and listen for fuel pump*
*Some vehicles have a pigtail
coming out of the wiring harness which can be connected to the positive battery terminal to energize the pump. If not, the fuel pump relay can be removed and a jumper wire can be installed across the switched side of the relay circuit.
Can hear pump
Canâ&#x20AC;&#x2122;t hear pump
Go to CHART 2
Go to CHART 3
CHART 2 Install fuel pressure gauge & energize fuel pump circuit*
Fuel pressure is below vehicle fuel system specifications
Fuel pressure is above vehicle fuel system specifications
Check fuel filter Replace if necessary
GO to CHART 4
Fuel pressure is within vehicle fuel system specifications
Return fuel system
Fuel pressure is below vehicle fuel system specifications
*Make sure the pressure gauge you use is rated for the specified fuel system pressure of the vehicle. Most vehicles willl have a Schrader valve on the fuel rail to hook a pressure gauge to. If it does not, refer to Figure 1A & 1B for correct gauge location.
Returnless fuel system
See Figure 1A
See Figure 1B
Pinch off return fuel hose
Fuel pressure remains within vehicle fuel system specifications
Fuel pressure is above vehicle fuel system specifications
GO to CHART 3
Pump is good
Figure 1A
Figure 1B
Return System
Fuel Pressure Regulator
Pressure Gauge Injector Rail
Returnless System
Pressure Gauge Injector Rail
Injectors
Injectors Return Fuel Line Fuel Tank
Fuel Pump Module
Supply Fuel Line
Fuel Tank
Fuel Pump Module
Supply Fuel Line
Caution: Gasoline is involved and vapors will settle in low areas, so work in a well ventilated space away from sparks or open flame such as a pilot light. Have a class B fire extinguisher close by. To eliminate the chance of fire or personal injury, the fuel system pressure must be relieved before servicing any fuel system component. Refer to the manufacturer's service manual for specific steps.
CHART 3 Perform voltage drop test*
Voltage drop exceeds 1.5 volts
Voltage drop less than 1.5 volts
Repair faulty connection and repeat voltage drop test
Remove fuel pump from vehicle and carefully inspect all connections that could not be reached during voltage drop test.**
*While performing the voltage drop test it is critical that the pump is still wired into the circuit. Failure to do this will make this test invalid. It is important to perform the voltage drop test on both the positive and negative sides of the circuit. Test points should be chosen to cover as much of the circuit as is possible to reach. (See Figure 2) **Inspect for melted insulation on wiring close to connectors. Check for melted plastic or black soot where positive and negative terminals enter the connector. This evidence indicates a bad connector. Check for loose connections where positive or negative wires attach to pump hanger bracket assembly.
Bad connection
No bad connections
Repair bad connection and re-install pump
Replace fuel pump
Go to CHART 2
Figure 2 Voltage Drop Test (-)
sum of the voltage drops of • The positive and negative side of the
circuit should not exceed 1.5 volts.
Battery
If it does. Check voltage drops • across each connector, relay, fuse,
Fuse
(+)
Connector
ground, and across the wiring for bad connection.
must be wired into circuit and • Pump energized during this test.
Relay
(-)
(+) Fuel Pump
Voltmeter
Voltmeter
Fuel Tank
CHART 4 Type of fuel system (See Figure 1A & 1B)
Returnless
Replace fuel pump or assembly
Return
Ford truck/van using P74107or P74108 pump
All other return applications
Remove return fuel hose and insert into container. Then energize pump.
Replace defective fuel pressure regulator or repair restrictions in return line
Fuel pressure still exceeds vehicle fuel system specifications
Fuel pressure within vehicle fuel system specifications
Replace fuel pressure regulator
Replace fuel pump or assembly
Caution: Gasoline is involved and vapors will settle in low areas, so work in a well ventilated space away from sparks or open flame such as a pilot light. Have a class B fire extinguisher close by. To eliminate the chance of fire or personal injury, the fuel system pressure must be relieved before servicing any fuel system component. Refer to the manufacturer's service manual for specific steps.
©2003 Federal-Mogul Corporation. Carter and the Federal-Mogul design are registered trademarks of Federal-Mogul Corporation. All rights reserved. Printed in U.S.A. 25714 7/03
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How to Diagnose & Repair Carburetor Problem
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How to Diagnose and Repair Carburetor Problems Copyright AA1Car A carburetor uses intake vacuum to supply fuel to the engine. As air is pulled down through the throat of the carburetor by intake vacuum, fuel is siphoned from the carburetor's fuel bowl and mixed with the incoming air to form a combustible mixture. At idle, the fuel enters the carburetor throat through one or small small idle ports just above the throttle plate. At higher engine speeds, fuel is pulled through the main metering jets into the venturi (the narrowest part of the carburetor throat). The air/fuel mixture then flows down through the intake manifold and into the cylinders where it is burned to produce power. Though the basic operation of a carburetor is fairly simple, it also relies on a number of add-on devices for cold starting, idle control and emissions. Changes in emission regulations in the early 1980s made carburetors obsolete because they were unable to meet the new emission requirements. By the mid-1980s, carburetors were history on new production vehicles, having been replaced by throttle body and multiport electronic fuel injection systems.
Carburetor Problems When a carburetor is clean and is working properly, the engine should start easily (hot or cold), idle smoothly, and accelerate without stumbling. The engine should get normal fuel economy and emissions should be within limits for the year of the vehicle. Problems that are often blamed on a "bad" or "dirty" carburetor include hard starting, hesitation, stalling, rough idle, flooding, idling too fast and poor fuel economy. Sometimes it is the carburetor and sometimes it is something else. Carburetors can be tricky to rebuilt, and expensive to replace, so you want to be sure of your diagnosis before you touch this critical part.
Hard Cold Starting Problems Hard starting can be caused by a choke that fails to close and causes a rich fuel mixture when the engine is cold. But there's no need to
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rebuild or replace the carburetor if all that's needed is a simple adjustment or cleaning of the choke mechanism and linkage. Chokes are very sensitive, and easily misadjusted (which is why the government required the auto makers to make choke and idle mixture adjustments "tamper-resistant" in the 1980s). Inside the choke housing is a coiled bi-metal heat-sensing spring that contracts when it cools and expand (unwinds) when it gets hot. The spring opens and closes the choke plate on top of the carburetor. The spring is inside a black plastic choke housing on the top or side of the carburetor. The spring is heated by an electric heating element inside the cover and/or heat from the exhaust manifold that is siphoned up into the housing through a small metal tube. If the heating coil has burned out or is not receiving voltage, or the heat riser is plugged with rust, loose or missing, the choke will not warm up properly. This will cause the choke to say on all the time, or too long, making the engine run rich and idle too fast.
If the bi-metal choke spring is broken, the choke will never close. A cold engine needs a very rich mixture to start, so if the choke isn't working it will suck too much air. A broken choke will also prevent the engine from idling properly (no fast idle while it is warming up) which can cause it to stall until it reaches normal operating temperature. If the shaft that opens and closes the choke is dirty, it may cause the choke to stick. The same goes for the choke linkage if it is dirty or damaged. Even if the choke is defective, a choke repair kit or a new bimetal spring should be all that's necessary to eliminate the starting problem. Replacing the entire carburetor is unnecessary and is the same as replacing the engine because the water pump is bad. Other causes of hard starting include vacuum leaks, ignition problems (worn or dirty spark plugs, bad plug wires, cap, rotor, etc.), low compression, even a weak starter or battery.
Hard Hot Starting Problems As for hot starting problems, the carburetor is seldom to blame. A hot start condition is usually the result of too much heat in the vicinity of the carburetor, fuel lines or fuel pump. Heat causes the fuel in the fuel lines, carburetor bowl or pump to boil. This creates a "vapor lock" condition which can make a hot engine hard to start. Replacing or rebuilding the carburetor wouldn't solve anything because the real culprit is heat. What needs to be done here is to reroute the fuel line away from sources of heat (like the exhaust manifold and pipe), and/or to insulate the fuel line by fabricating aheat shield or wrapping the fuel line with insulation. Hot start problems can also be caused by excessive resistance in a starter, poor battery cable connections, or a faulty ignition module that acts up when it overheats.
Hesitation or Stumble When Accelerating Hesitation is a classic symptom of a lean fuel mixture (too much air, not enough fuel) and can be caused by a dirty or misadjusted carburetor, or one with a weak accelerator pump or worn throttle shafts. Rebuilding or replacing the carburetor may be necessary. The accelerator pump squirts and extra dose of fuel into the throat of the carburetor when the throttle opens. This helps offset the extra gulp of air that is sucked in until fuel flow through the metering circuits can catch up to the change in air velocity through the venturi (the narrow part of the carburetor throat). The accelerator pump may use a rubber diaphragm or a rubber cup on a piston to pump fuel through its discharge nozzles. If the diaphragm is torn or the piston piston seal is worn, the accelerator pump may not deliver it's normal dose of fuel. Or, if the discharge nozzles are plugged with dirt or fuel varnish deposits, it can restrict fuel flow. The operation of the accelerator pump can be checked by removing the air filter, looking down into the carburetor, and pumping the throttle. You should see a jet of fuel squirt into each of the front venturis (barrels) of the carburetor. If no fuel squirts out, or the stream is very weak, or only one of the two discharge nozzles on a two-barrel or four-barrel carburetor are working, the accelerator pump circuit has a problem. Fuel usually enters the accelerator pump past a one-way steel check ball. The ball lets fuel in, but is pushed back against its
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How to Diagnose & Repair Carburetor Problem
seat by pressure inside the pump when the throttle opens. If this check ball is stuck open, it acts like a pressure leak and prevents the accelerator pump from squirting fuel through the discharge nozzles. If the check ball is stuck shut, it will prevent fuel from entering the pump and there will be no fuel to pump through the discharge nozzles. If the carburetor jets are coated with fuel varnish deposits, or there is dirt inside the fuel bowl, this can restrict the flow of fuel causing a lean condition. Cleaning the carburetor with carburetor cleaner can get rid of the dirt and varnish deposits to restore normal operation. Air leaks elsewhere on the engine can also lean out the fuel mixture. Air can enter the intake manifold through loose or cracked vacuum hoses, emission hose or the PCV system. Vacuum leaks in the carburetor base gasket or insulator, intake manifold gaskets, power brake booster or other vacuum accessories can admit unwanted air. Air can even get into the manifold past badly worn valve guides and seals. A defective EGR valve that fails to close at idle or when the engine is cold can be another cause of hesitation. Other causes may include a defective distributor advance mechanism, a weak ignition coil, carbon tracks on the coil tower or distributor cap, bad plug wires, worn or dirty spark plugs that misfire when the engine is under load, or even an exhaust restriction. Even bad gas can cause hesitation problems. So before the carburetor is rebuilt or replaced, these other possibilities need to be investigated an ruled out.
Hesitation Under Load A hesitation, stumble or misfire that occurs when the engine is under load can be caused by a faulty power valve inside the carburetor. A carburetor uses intake vacuum to pull fuel through its metering circuits. As engine load increases and the throttle opens wider, intake vacuum drops. This can reduce the flow of fuel and make the fuel mixture go lean, so the power valve has a spring-loaded vacuum-sensing diaphragm that opens to increase fuel flow when vacuum drops. If the diaphragm has failed or the valve is clogged with dirt or fuel varnish deposits, it must be replaced. A new power valve is usually included with a carburetor rebuild kit. Hesitation or misfiring under load can also be caused by a weak ignition coil, or cracks in the coil or distributor cap, or bad spark plug wires.
Stalling An engine can stall if the idle speed is too low, the fuel mixture is too lean, won't burn, stops flowing or the ignition system runs out of spark. Rebuilding or replacing the carburetor won't eliminate this problem if stalling is ignition related or due to a weak fuel pump, plugged fuel filter or fuel line, or bad gas (too much water or alcohol). A simple adjustment may be all that's needed to increase the idle speed or richen the idle mixture. But if the engine is sucking air through a vacuum leak somewhere, no amount of adjustment may totally eliminate the tendency to stall. The vacuum leak must be found and fixed before accurate idle speed and mixture adjustments will be possible. The carburetor may have to be rebuilt or replaced if there are internal air leaks in the carburetor itself, a sticky needle valve is starving the carburetor for fuel, or the jets, air bleeds or metering passageways in the carburetor are dirty or plugged. Replacement would be required if the throttle shafts are badly worn, or the carburetor housing is warped or damaged. On vehicles with computer-controlled idle speed, an inoperative or defective idle speed control (ISC) motor can make an engine stall. The ISC motor is supposed to maintain the desired idle speed by repositioning the throttle linkage. A bad electrical connection or wiring problem can prevent the motor from doing it's job. If the ISC motor is receiving voltage and is properly grounded but doesn't budge, then the motor is burned out and needs to be replaced. The motor may have failed because a vacuum leak caused it to overtax itself in a vain attempt to compensate for the unwanted air.
Rough Idle A rough idle condition is usually caused by an overly lean fuel mixture that results in lean misfire. A common cause of idle problems is air leaks between the carburetor and intake manifold (tighten the carburetor base bolts or replace the gasket under the carburetor), air leaks in vacuum lines or the PCV system or EGR valve. Other carburetor-related causes include an idle mixture adjustment set too lean (back out the idle mixture adjustment screw one quarter of a turn at a time until he idle quality improves), or a dirty idle mixture circuit (which may require cleaning and rebuilding the carburetor). Other possible causes of a rough idle include a defective charcoal canister purge control valve that is not closing and is leaking fuel vapors back into the carburetor, excessive compression blowby (worn rings or cylinders), weak or broken valve springs, or ignition misfiring due to worn or dirty spark plugs, bad plug wires or a weak ignition coil.
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How to Diagnose & Repair Carburetor Problem
Flooding This is a problem that is usually (but not always) the carburetor's fault. The carburetor may flood if dirt enters the needle valve and prevents it from closing. With no way to shut off the flow of fuel, the bowl overflows and spills fuel into the carburetor throat or out the bowl vents. A flooded engine may not start because the plugs are wet with fuel. WARNING: Flooding can be a very dangerous situation because it creates a serious fire hazard if fuel spills out of the carburetor onto a hot engine. A carburetor can also flood if the float inside the fuel bowl is set too high or develops a leak and sinks (this applies to hollow brass or plastic floats primarily). If all that is needed is a new float, there is no real need to replace the entire carburetor. Floats are not part of a rebuild kit, so if new gaskets are also needed, a rebuild kit will have to be purchased, too. Flooding can also be caused by excessive fuel pressure forcing fuel past the needle valve. Flooding may also be caused by excessive heat in some instances. A heat riser valve on a V6 or V8 engine that sticks shut may create a hot spot under the intake manifold that causes the fuel in the carburetor bowl to boil over and flood the engine.
Idles Too Fast This type of idle problem usually caused by the automatic choke. If the choke is sticking, the engine will stay at fast idle too long. Inspect the choke and choke linkage, and clean or repair as needed. There is a separate fast idle adjustment screw on the choke linkage that controls engine speed while the engine is warming up. The tip of the screw rests against a cam that slowly rotates as the choke opens during engine warm up. Turn this screw counterclockwise to decrease the fast idle speed, or clockwise to increase fast idle speed. A high idle speed can also be caused by vacuum leaks that allow air to enter the manifold (leaky PCV hose, power steering booster hose or other large vacuum hose). Another cause may be a defective ISC motor stuck in the extended (high idle speed) position.
Poor Fuel Economy Don't blame the carburetor if the real problem is a lead foot on the accelerator pedal , or the engine has low compression, retarded ignition timing or an exhaust restriction (plugged converter). But if nothing else is wrong, the carburetor may have a misadjusted or heavy float, or the wrong metering jets (too large). The float setting determines the fuel level in the bowl, which in turn affects the richness of the air/fuel mixture. A float that is set too high or has become saturated with fuel (a problem that continues to plague many foam plastic floats today), allows the fuel level to rise and richen the fuel mixture. To diagnose this condition, the float level needs to be checked and the float weighed to determine if it has become fuel saturated. If the float is heavy, it needs to be replaced. With electronic feedback carburetors, a sluggish or dead oxygen sensor can make the fuel mixture run rich. So too can a defective coolant sensor that never allows the feedback system to go into closed loop. Scanning for fault codes and checking the operation of the feedback system can rule out these possibilities. If the carburetor has been replaced recently with a used carburetor or a carburetor off another engine, the jets may not be calibrated correctly for the new application. Bigger jets flow more fuel and richen the fuel mixture. Installing smaller sized jets may restore the proper air/fuel mixture and good fuel economy. One way to tell if the fuel mixture is too rich or too lean is to examine the spark plugs. If the plugs have heavy black, sooty carbon deposits on the electrodes, the fuel mixture is too rich. If the mixture is too lean, the ceramic insulator around the center electrode may be yellowish or blistered in appearance. An overly lean air/fuel mixture is bad because it can cause engine-damaging preignition and detonation.
Rebuild or Replace Carburetor If the carburetor needs work, it can be rebuilt with a kit or replaced with a new or remanufactured carburetor. Replacement carburetors are expensive, and may cost from $200 to $600 or more depending on the application and type of carburetor. Cleaning and rebuilding an older one or two barrel carburetor is a relatively simple job. A four barrel is a little more difficult. More complicated carburetors such as those with a variable-venturi or electronic feedback controls and tamper-resistant
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How to Diagnose & Repair Carburetor Problem
adjustments can be very difficult to rebuild, and may require the skills of an expert. It is often easier and less risky to replace a more complicated carburetor than to attempt a rebuild. If the carburetor has worn throttle shafts that are leaking air, or any of the castings are cracked, warped or damaged, the carburetor cannot be rebuilt and must be replaced. The only alternative here is if you have a second carburetor you can cannibalize for parts to salvage and repair the first carburetor. Whether you are rebuilding or replacing a carburetor, you first need to identify it. Year, make, model and engine size may not be enough information to find the correct carburetor kit or replacement carburetor. There is usually a small metal ID tag on the carburetor that will tell the exact model number and calibration of the unit.
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Carburetor Rebuilding Tips Before you take a carburetor apart, find an assembly diagram in a service manual for reference. Carburetor kits may or may not include an assembly diagram and instructions. Click Here to see exploded views of common carburetors (link to Carburetor Factory). Also note where various vacuum hoses and lines connect to the carburetor. If necessary, draw a picture of the hose connections, or place a piece of masking tape on each hose and write on the tape which hose goes where. Lay the parts out on a clean work bench, paper or metal tray. Pay attention to how the parts came apart (especially linkages) so you can remember how to reassemble the parts when you put the carburetor back together. Watch out for small steel check balls that can be easily overlooked or lost. When cleaning carburetor parts, use carburetor cleaner or a solvent that will not damage plastic and soft metal parts. Wear rubber gloves to avoid skin contact with the cleaner or solvent. Follow use instructions for the cleaner or solvent, and use in a
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How to Diagnose & Repair Carburetor Problem
well ventilated area. Avoid breathing the fumes.
Carburetor Installation Tips Clean the carburetor mounting surface on the intake manifold (do NOT allow any dirt or gasket debris to fall down inside the manifold), and install a new base gasket under the carburetor (never reuse the old gasket because they almost always leak). Gasket sealer may be applied to the base gasket to reduce the chance of air leakage, but do NOT use RTV silicone because it dissolves when exposed to gasoline. Tighten the carburetor base mounting nuts or bolts evenly so the gasket is clamped firmly in place. Do NOT over-tighten the fasteners as doing so may warp or crack the carburetor base plate. When reconnecting the fuel line and any other fittings (EGR, PCV) to the carburetor, be careful not to cross-thread the fittings, and do NOT over-tighten as doing so can strip the treads in the soft casting. Install a new fuel filter to protect the carburetor from dirt. Do NOT forget to reattach the throttle return spring(s) on the throttle linkage. The last thing you want is a runaway engine when you start it up. If the springs are old and rusty, appear to be stretched or are weak, replace them with new springs. Also test the throttle linkage to make sure the throttle opens all the way when the gas pedal is floored, and that nothing binds or rubs against the linkage that might cause it to stick. When installing the air cleaner, do NOT over-tighten the nut that holds the air cleaner in place as this can distort and damage the carburetor casting. Inspect all rubber fuel hoses and clamps. Replace any hose that is hard, brittle, mushy, cracked or leaking. New clamps are also recommended. Worm-screw clamps are usually the best. Ring style clamps lose tension with age, and can be permanently deformed if they are over-expanded during removal. Double check all the fuel line, vacuum and emission hose connections, the throttle linkage and return spring, then start the engine. Recheck again for any leaks or other problems.
Carburetor Adjustment Tips Adjust the idle speed and idle mixture adjustment screws after the engine reaches normal operating temperature. Set the idle speed to specifications (typically 550 to 650 rpm), and adjust the idle mixture screws for smoothest idle. Turn each idle mixture screw in until the engine starts to stumble, then back it out about 1/4 to 1/2 turn. The automatic choke may have to be adjusted if the engine does not start easily. The choke should be fully closed on a cold engine, and open all the way once the engine warms up. Small adjustments go a long ways, and it may take several trialand-error adjustments of the choke housing to get it right. If the engine hesitates or stumbles when accelerating, the accelerator pump linkage or cam may require some adjustment to increase the volume of fuel squirted into the engine when the throttle opens. The accelerator pump linkage or cam usually has several adjustment settings, so try the next higher setting if it needs more fuel. If you are installing a performance carburetor, the main metering jets that come in the carburetor may or may not give you the best air/fuel mixture. The best performance is usually achieved with a slightly rich mixture. Jet sizes are usually indicated with a number stamped on the side of the jet. Installing slightly larger sized jets will flow more fuel and richen the mixture. If the carburetor is running too rich, then switching to slightly smaller sized jets may give better performance. Replacing the main metering jets usually requires removing the top of the carburetor or the fuel bowls. Some racing carburetors have jets that can be replaced without disassembly.
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Engine Scopes
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Engine Scopes (Digital Storage Oscilloscopes) Copyright AA1Car Adapted from an article written by Larry Carley for Underhood Service magazine
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.. A "digital storage oscilloscope" (DSO), also known as a "dual trace scope," is unquestionably one of the most useful pieces of diagnostic equipment that is available today. What makes them so valuable as a diagnostic aide is their ability to capture and display electronic signals as waveforms on a screen. If a picture is worth a thousand words, then a waveform ought to be worth at least several pages of diagnostic flow charts and God knows how many hours of time testing individual components and circuits in an attempt to identify and isolate a problem. One waveform can often give you a clear picture of exactly what is happening inside a sensor or the onboard computer system. That is the power of a scope.
WHAT SCOPES CAN & CANNOT DO First things first. A scope is not a substitute for a scan tool, an engine analyzer, an exhaust analyzer, a digital multimeter, a breakout box or any other piece of diagnostic equipment you may already own. These are all essential tools for underhood diagnosis today. A scope complements all of these other tools by giving you yet another means of peering into the inner workings of the onboard electronics. A scan tool can display fault codes or messages as well as voltages and other values by translating the serial data that comes out of the vehicle onboard computer. You can look at all kinds of numbers and data, but the numbers alone don't always give you a complete picture of what is really going on inside the system, especially when you are dealing with an intermittent fault or a momentary fault. What's more, many problems won't even set a fault code. So you may not have a clue as to where to start if you are trying to fix a driveability or emissions problem. The drawback to using scan tool serial data to diagnose sensor problems and other faults within the onboard electronics is that serial data is not "real" data. It is the computer's interpretation or report of what it thinks it sees, which may not necessarily be what is really going on electronically in its input and output circuits.
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For example, say a car has a hesitation problem and you suspect the throttle position sensor (TPS). You look at the output voltage of the TPS with your scan tool and watch the numbers increase then decrease as you open and close the throttle. The TPS seems to be okay, but is it? If there is a momentary dead spot in the TPS (which typically occurs between idle and part throttle where wear is greatest), the serial data that you are seeing may not reveal the dead spot in the TPS. Even if you are using an analog voltmeter to read the TPS directly, the needle may not respond fast enough to detect a momentary dead spot. Sometimes a TPS will read fine when opening and closing the throttle slowly, but skips when the throttle is snapped opened quickly. But you may never see the glitch unless you have a means of viewing the TPS output signal itself. What a scope does is translate an electronic signal into a pattern or waveform on a screen. As the waveform is traced across the screen, it creates a signature of the signal's characteristics (more on this subject in a minute). The waveform reveals a tremendous amount of useful information about what is actually going on electronically within the sensor or circuit. So once you know what to look for, you can quickly distinguish good signals from bad ones.
A LEARNING EXPERIENCE Reading waveforms isn't something you are going to pick up overnight, however. If you thought learning how to use a scan tool was fun, wait until you are confronted with a scope for the first time. The initial setup procedure can be intimidating, but the menu driven setup screens in most scopes helps simplify the process. Instead of entering vehicle year, make and model or VIN number as you would with a scan tool, you tell the scope how to display the signal data. This includes setting the voltage scale and time base. A scope displays voltage on the vertical scale and time along the horizontal scale. You pick a voltage scale and time base that allows you to see the entire waveform and also makes it large enough so you can see all the important details. Next, you have to tell the scope when to start displaying the signal unless this is done automatically (which it is on some scopes). This point is called the "trigger level" and is set to a specific voltage value. You also have to tell the scope which way to draw the pattern (up or down) when the signal voltage passes the trigger level. All this may sound rather confusing to the uninitiated, but once you have figured out how the scope works it is no more difficult to setup and use than a scan tool. It is getting over the initial hump that scares off many would-be scope users. Another thing that is different with a scope is how you hook it up to the vehicle. Unlike a scan tool that simply plugs into a diagnostic connector somewhere on the vehicle, the scope leads require you to either backprobe connectors or pierce the wiring of individual sensors or circuits. Most vehicle manufacturers d not like technicians poking holes in wires. Even so, if you use "Hirschmann" style probes, they make only tiny holes in the wiring which can be easily resealed afterwards with a dab of nail polish (just what every technician carries in his toolbox, right?). In addition to learning how to use the scope itself, you also have to learn about electronic signals and waveforms. For starters, you have to know what the five basic types of electronic signals are: direct current (DC), alternating current (AC), fixed pulse width (variable frequency), pulse width modulated and serial data. Then you have to learn what each of these signals looks like on a scope as well as the "critical dimensions" that are important for each signal's waveform (what you are supposed to look at in other words). This includes signal amplitude, frequency, shape, pulse width and overall pattern. Still with me? I hope so. Then you have to learn what the basic waveforms for each type of sensor and other device are supposed to look like. This is the hard part because waveforms vary a great deal depending on the vehicle application. Different types of fuel injector drivers, for example, produce different waveform signatures. Some produce a single spike when the computer opens the ground circuit (saturated switch type injector drivers like those used with Bosch multiport systems), some produce a double spike (peak and hold type drivers such as those used with GM throttle body injectors), and some produce an inverted spike (like the "backwards" style Jeep 4.0L multiport injectors that are normally grounded and open when energized with voltage through the computer driver circuit). Why do you have to know all this stuff? Because the height of the voltage spike as well as where it occurs on the waveform can reveal electrical problems within the injector solenoid or computer driver circuit. A shorter than normal spike, for example, would be characteristic of a partially shorted injector solenoid. A simple resistance check with an ohmmeter might not reveal such a problem. This is just one example of the many things you can't see with a scan tool or multimeter but you can see with a scope. You will also find the learning curve requires a certain amount of hands-on experience with a variety of vehicles. A relatively inexperienced user can easily identify a "flat liner" or an obviously bad sensor signal. But it takes an experienced eye to distinguish a marginal waveform that may be causing trouble. What may be normal "noise" in the waveform on one application may be unacceptable "hash" in the waveform of another. This is especially true when looking at oxygen sensor waveforms which give you more diagnostic insight into the overall health of the onboard computer system than any other individual signal. So until you develop an eye for reading waveforms, it helps to have a library of good waveforms for http://www.aa1car.com/library/us296.htm
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Engine Scopes
comparison and reference. The fastest way to get up to speed on scopes is to attend a clinic put on by one of the scope manufacturers, or to take a self-study course. One of the best self-study courses I have seen is NAPA's "Using the digital storage oscilloscope to master driveability and emissions diagnosis" training program (part number 6212). The workbook and video tape will really open your eyes to what a scope can do, and even includes repair case histories that show how a scope can be used to diagnose kinds of problems.
SNAP SHOTS One of the attributes of a digital storage scope that makes it such a valuable diagnostic tool is its ability to capture and store signal waveforms. Analog lab scopes with cathode ray tube (CRT) displays are good at showing signal patterns in real time, which is why they have long been used with engine analyzers to display ignition patterns. But using an analog scope to display electronic signals has some drawbacks. One is that analog scopes can't be configured to slow or freeze a waveform display. If a momentary glitch occurs, there is no way to capture and analyze it. It is there, then zip it is gone. And it may have happened so quickly that you didn't even notice it. A digital scope, by comparison, does not display a signal in real time. There is a slight delay, the length of which varies depending on how "fast" the scope is. Though this may seem like a disadvantage, it is actually an advantage when it comes to capturing events that happen very quickly because it can slow the events down so we can see them more easily. Unlike an analog scope that uses the input signal to continuously shape the waveform display, a digital scope takes little samples or snippets of information from the signal, then processes the bits to paint a waveform picture dot by dot across the screen. The end result is a "cleaner" waveform with less noise to garbage it up. This makes it much easier to analyze the waveform and compare it to other previously captured and stored waveforms. The sampling rate with a digital scope is normally around 25 million samples per second, which is fast enough to catch even the most momentary glitch. Depending on the scope, this can usually be increased to an even higher rate. Some scopes offer a "spike detect" mode which jumps the sampling rate up to once every billionth of a second! At this rate, the waveform contains much more detail and noise, but also reveals problems that might be overlooked in the normal sampling mode. Most digital scopes are also hand-held units with LCD displays, which makes them easily portable. If you think a scan tool or flight recorder can help you catch a momentary glitch during a test drive, you have not seen anything until you have taken along a scope. You will see things you have never seen before, and catch problems you would have never caught before.
O2 WAVEFORMS One of the most powerful uses for a scope, however, is one we have not even mentioned yet: looking at the oxygen sensor signal. A scope can tell you if the O2 sensor is capable of producing a good signal even if the sensor is reading rich or lean. The scope can also allow you to use the O2 sensor waveform to verify that the computer feedback fuel control loop is functioning properly. Of course, you can do the same thing with a scan tool, but not with the same degree of accuracy as a scope. And what if a vehicle has no data stream output for a scan tool or the O2 sensor? Then what? When you look at an O2 sensor's output with a scan tool, you see only a voltage value or a rich or lean indication. You can also look at cross counts to see if the sensor is flip-flopping back and forth from rich to lean at an acceptable rate. You can also check the sensor's rich and lean response by making the fuel mixture rich (by feeding propane into the intake manifold) and then lean (by pulling off a vacuum hose) to see if the sensor responds as it should. Yet a sensor that passes all these tests may still be causing problems if its waveform is bad or full of noise. That is where a scope comes in. It shows you everything you need to know about the sensors output in one simple picture. You can see at a glance if the sensor is reading rich or lean, what the sensor's peak and minimum voltages are, if the sensor is flip-flopping from rich to lean at a normal rate, and how it responds to changes in the fuel mixture. You can also see if the signal is clean or full of noise. If the scope has dual trace capability, you can also display the injector driver waveforms at the same time to see if the feedback loop is changing injector duration in response to changes in the the O2 sensor signal.
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AN EKG FOR THE ENTIRE SYSTEM Like an EKG reveals an irregular heartbeat, the O2 sensor waveform will also reveal any underlying problems such as vacuum leaks, ignition misfire, injector imbalance and even compression losses. Each of these conditions will produce a characteristic type of hash in the sensor waveform. Anytime a cylinder misfires or leaks compression, unburned oxygen enters the exhaust. This shows up as a momentary dip in the O2 sensor's output voltage. So if the O2 sensor's waveform contains lots of little inverted spikes, it tells you the engine is misfiring or leaking compression. You can then use your other diagnostic equipment to nail down what is causing the problem.
OTHER USES A scope can also be used as a repair verification tool. If you "baseline" a vehicle before repairs are made (capture the O2 or other sensor waveform that reveals a problem), you can then compare "before" and "after" waveforms to make sure the problem has been corrected. An O2 sensor and feedback loop diagnostic scope check should be part of every tune-up as well as every driveability and emission repair you do. Those who use a scope this way say it eliminates most comebacks. You can also use a scope to check the "V-ref" voltage in sensor circuits. Unlike a digital voltmeter that only gives you a number, the V-ref voltage on a scope appears as a flat horizontal line. Though not very interesting to look at, it can reveal hidden problems if the line is full of noise, has spikes or breaks up. The same technique can also be used to check battery voltage and wiring continuity. If the line breaks up or dips when you wiggle a connector, it tells you there is a problem. A scope can also help you spot bad alternator diodes. The normal AC output pattern of the alternator should look like top of a picket fence. If any tops missing, it indicates one or more bad diodes. You can even use a scope to read serial data, though not in the same way as a scan tool. A scan tool has software that converts serial data into letters and numbers we can read. A scope cannot do that. All it will show you is an irregular square waveform as the data stream passes by. Even so, this can tell you the computer is producing a data stream (should your scan tool not be displaying anything). It can also tell you if the computer is shutting down when the ignition is turned off. If you continue to see data stream up to a minute or more after the key has been switched off, the computer is not powering down as it should. The power relay is probably stuck on and may be draining the battery. Buying a Scope Digital storage scopes are not cheap. Most cost $2200 to $2800 or more, which is more than some professional grade scan tools. So it is hard to justify making such an investment unless you are a professional technician and are doing a lot of diagnostic work. The least expensive way to buy a scope is to buy a combination professional grade scan tool that also has a built-in scope.
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Distributorless Ignition System
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Distributorless Ignition Systems (DIS) Copyright AA1Car Distributorless ignition systems (DIS) have been around for almost a decade now, and have eliminated much of the maintenance that used to be associated with the ignition system. No distributor means there is no distributor cap or rotor to replace, and no troublesome vacuum or mechanical advance mechanisms to cause timing problems. Consequently, DIS ignition systems are pretty reliable. Even so, that does not mean they are trouble-free. Failures can and do occur for a variety of reasons. So knowing how to identify and diagnose common DIS problems can save you a lot of guesswork the next time you encounter an engine that cranks but refuses to start, or one that runs but is missing or misfiring on one or more cylinders. If an engine cranks but will not start, is it fuel, ignition or compression? Ignition is usually the easiest of the three to check because on most engines, all you have to do is pull off a plug wire and check for spark when the engine is cranked. On coilover-plug DIS systems, there are no plug wires so you have to remove a coil and use a plug wire or adapter to check for a spark.
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Distributorless Ignition System
If there is no spark in one cylinder, try another. No spark in any cylinder would most likely indicate a failed DIS module or crankshaft position (CKP) sensor. Many engines that are equipped with electronic fuel injection also use the crankshaft position sensor signal to trigger the fuel injectors. So, if there is no spark and no injector activity, the problem is likely in the crank position sensor. No spark in only one cylinder or two cylinders that share a coil would tell you a coil has probably failed.
DIS COIL CHECKS The coils in DIS ignition systems function the same as those in ordinary ignition systems, so testing is essentially the same. But the driveability symptoms caused by a weak coil or dead coil will be limited to one or two cylinders rather than all the cylinders. Many DIS systems use the "waste spark" setup where one coil fires a pair of spark plugs that are opposite one another in the firing order. Others, including the newer coil-over-plug systems, have a separate coil for each spark plug. Individual DIS coils are tested in essentially the same way as epoxy-filled (square-type) ignition coils. First, isolate the coil pack by disconnecting all the leads. Set the ohmmeter in the low range, and recalibrate if necessary. Connect the ohmmeter leads across the ignition coil primary terminals, and compare the primary resistance reading to specifications (typically less than 2 ohms). Then connect the ohmmeter leads across the coil secondary terminals and compare the secondary resistance reading to specifications (typically 6,000-30,000 ohms). If readings are outside the specified range, the coil is defective and needs to be replaced. If measuring the secondary resistance of a DIS coil is difficult because of the coils location, try removing the wires from the spark plugs and measure secondary resistance through the plug wires rather than at the secondary terminals on the coils. Just remember to add in a maximum of 8,000 ohms of resistance per foot for the plug wires.
DIS MODULE & SENSOR CHECKS
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Here is a little trick that will literally show you if a DIS module and its crankshaft sensor circuit are working: connect a halogen headlamp to the spade terminals that mate the DIS module to the coils. A headlamp is recommended here because it puts more of a load on the module than a test lamp. If the headlamp flashes when the engine is cranked, the DIS module and crankshaft position sensor circuit are functioning. Therefore, the problem is in the coils. If the headlamp does not flash, or there is no voltage to the module or coil pack when the engine is cranked, the problem is most likely in the crankshaft sensor circuit. On most vehicles, a bad crank position sensor will usually set a fault code, so use a scan tool to check for a code. Or, check the crank sensor itself. Magnetic crank sensors can be tested by unplugging the electrical connector and checking resistance between the appropriate terminals. If resistance is not within specs, the sensor is bad and needs to be
replaced. Magnetic crank position sensors produce an alternating current when the engine is cranked so a voltage output check is another test that can be performed. With the sensor connected, read the output voltage across the appropriate module terminals while cranking the engine. If you see at least 20 mV on the AC scale, the sensor is good, meaning the fault is probably in the module. If the output voltage is low, remove the sensor and inspect the end of it for rust or debris (magnetic sensors will attract iron and steel particles). Clean the sensor, reinstall it and test again. Make sure it has the proper air gap (if adjustable) because the spacing between the end of the sensor and the reluctor wheel or notches in the crankshaft will affect sensor output voltage. If the air gap is correct and output is still low, replace the sensor. Hall effect crankshaft position sensors typically have three terminals; one for current feed, one for ground and one for the output signal. The sensor must have voltage and ground to produce a signal, so check these terminals first with an analog voltmeter. Sensor output can be checked by unplugging the DIS module and cranking the engine to see if the sensor produces a voltage signal. The voltmeter needle should jump each time a shutter blade passes through the Hall effect switch. If observed on an oscilloscope, you should see a square waveform. No signal would tell you the sensor has failed.
DIS PERFORMANCE PROBLEMS In instances where the engine starts and runs but does not perform well (lack of power, poor fuel economy, spark knock,
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elevated emissions, etc.), the problem may be outside the DIS system. First, the individual coils should be tested to make sure their primary and secondary resistance is within specs. If the coils are all okay, the electronic spark control circuit may be receiving bad information from another sensor. Low MAP sensor output voltage or a coolant sensor that reads cold all the time will allow more spark advance than normal. This, in turn, may cause detonation (spark knock) problems when the engine is under load. So too can a faulty knock sensor or an EGR valve that is not working. High MAP output voltage or a misadjusted throttle position sensor can have the opposite effect and cause the spark control system to retard timing more than normal. Retarded timing will reduce performance and fuel economy. Do not forget, too, that ordinary secondary ignition problems can also cause misfires with DIS the same as a conventional ignition system. A bad spark plug wire or a worn or fouled spark plug will act just like a weak or bad DIS coil. So anytime you find an ignition problem that is isolated to a single cylinder, remove and inspect the spark plug and plug wire to rule out those possibilities.
GM Distributorless Ignition System Diagnosis The following video is provided courtesy of Wells Manufacturing via YouTube:
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Coil-On-Plug Ignition
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Coil-On-Plug (COP) Ignition Copyright AA1Car First it was the distributor that vanished. Now plug wires are starting to disappear. What is next, the spark plugs? The answer is yes, but that will not happen until direct fuel injection systems that combine the injector and spark plug into one assembly start appearing in a few years. In the meantime, you will have to learn how to diagnose and repair the current generation of coil-on-plug (COP) ignition systems. Spark plugs wires are going away for the same reason that distributors went away. Vehicle manufacturers want to reduce costs and improve ignition performance and reliability. Plug wires are an assembly line nuisance, and are often the weak link in distributorless ignition systems. The plug wires must carry anywhere from 5,000 up to 40,000 or more volts to fire the plugs. This requires heavy insulation plus the ability to suppress electromagnetic interference (EMI). The wires must also be coated with a tough outer jacket to withstand high temperatures in the engine compartment and chemical attack. As reliable as todays plug wires are, there is always the potential for trouble. Even the toughest insulation can burn if a wire rubs up against a hot exhaust manifold. The connection inside the spark plug boot between the wire and plug terminal can also be damaged if someone jerks on the wire to remove the boot when changing spark plugs. Plug wires can also radiate magnetic fields that may affect nearby sensor wires or other electronic circuits. Attaching the ignition coils directly to the spark plugs eliminates the need for separate high voltage wires along with their potential for trouble. Eliminating the individual plug wires also eliminates the need for wire looms and heat shields. That is why coil-on-plug ignition systems are being used on a growing number of late model engines.
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Coil-On-Plug Ignition
Coil-On-Plug ignition system on a General Motors Vortec 3500 engine. Getting rid of the plug wires not only saves money, it also improves the durability of the ignition system. No high voltage wires means no voltage leaks and no misfires due to "bad" plug wires. Using individual coils for each spark plug also means the coils have more time between each firing. Increasing the "coil saturation" time (the time the voltage to the coil is on to build up its magnetic field) increases the coil output voltage at high rpm when misfire is most apt to occur under load. Chrysler says its COP ignition system on its LHS and 300M engines delivers 28% more spark energy than earlier ignition systems. This improves combustion and reduces the risk of misfire with lean fuel mixtures (lean mixtures require more voltage to ignite reliably). COP ignition systems are used on many late model engines. On most applications, the plugs and coils are located on top of the cylinder head for easy mounting of the coils. A topside location is best because it keeps the coils away from the heat of the exhaust. This is the type of configuration Chrysler uses on its late model 2.7L, 3.2L and 3.5L engines in the Chrysler Intrepid, LHS and 300M models. Some other applications with COP ignitions include General Motors "Integrated Direct Ignition" (IDI) found on the 1988 through 1995 2.3L Quad Four engine, and the 1996 and newer 2.4L engine single overhead cam engine that replaced the Quad Four, 1997 and newer Cadillac Catera 3.0L, 1998 and up Lincoln Town Car 4.6L, 1996 and up Ford Taurus 3.4L, and many import nameplates including late model Acura, Honda, Infiniti, Isuzu, Lexus, Nissan, Saab and Toyota. Many engines cannot be equipped with COP ignitions because the location of the spark plugs does not leave enough room to mount individual coils over the plugs, or the plugs are too close to the exhaust manifold. For example, on the current "Gen III" small block V8 in Corvette, Camaro and Firebird, the spark plugs are located on the side of the cylinder heads and surrounded by the exhaust manifolds. There is no room to mount the coils directly on the plugs, so GMs engineers put the coils on the valve covers and connected each coil to its spark plug with a short wire. This is called a Coil_Near_Plug or CNP ignition system.
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Coil-On-Plug Ignition
A Coil-Near-Plug ignition system on a General Motors V8.
COIL-ON-PLUG IGNITION SYSTEM COMPONENTS
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In a typical COP ignition system, a crankshaft position (CKP) sensor generates a basic timing signal by reading notches on the crankshaft, flywheel or harmonic balancer. The crank sensor signal goes to the powertrain control module (PCM), where it is used to determine firing order and turn the individual ignition coils on and off. On Chrysler 2.7, 3.2 & 3.5L COP applications, an additional timing signal is needed from a camshaft position sensor located in the timing belt housing cover just above the left camshaft sprocket.
Chrysler crankshaft position sensors produce a square wave signal that goes from a high of 5.0 volts to a low of 0.3 volts. The sensor is located on the passenger side of the transaxle housing so it can read three sets of slots in the flywheel. Two sets contain 4 slots each, and one set contains 5 slots for a total of 13 slots. Basic timing is set by the position of the last slot in each group. Once the PCM detects the last slot, it determines which piston is next in the firing order from the camshaft position sensor. This means the engine may have to crank at least one revolution before the PCM can sort out the proper firing order and start zapping the plugs. Chrysler also uses an Auto Shutdown Relay (ASD). The ASD relay routes battery power to the ignition coils, and is energized by the PCM as long as receives signals from both the crankshaft and camshaft position sensors. If the engine stops turning (stalls), the PCM deengerizes the ASD relay and shuts down the ignition system. The ASD relay also supplies battery voltage to the fuel injectors, so when it shuts down it cuts off both ignition and fuel. At the same time, the PCM also deenergizes the fuel pump relay to turn off the fuel pump. For "limp in" capability, the Chrysler system can run with input from the crankshaft position sensor only. The ASD and fuel pump relays are both located in the Power Distribution Center. The operation of the ignition system is essentially the same as any other ignition system. Each coil has a low primary resistance (0.4 to 0.6 ohms in the case of Chrysler), and steps up the primary system voltage from 12 volts to as much as 40,000 volts to produce a spark for the spark plug. On the Chrysler COP systems, there is also a coil capacitor for each bank of coils for radio noise suppression. The only real difference between COP and other ignition systems is that each COP coil is mounted directly atop the spark plug so the voltage goes directly to the plug electrodes without having to pass through a distributor or wires. It is a direct connection that delivers the hottest spark possible. Resistor plugs are generally used to suppress EMI.
COIL-ON-PLUG IGNITION MISFIRES http://www.aa1car.com/library/copign.htm
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COP problems can include many of the same ailments as other ignition systems such as misfiring, hard starting or a no start. Spark plugs can still be fouled by oil or fuel deposits as well as preignition and detonation. So COP ignition systems are not immune to trouble. If the crankshaft position sensor fails, the loss of the basic timing signal will prevent the system from generating a spark and the engine will not start or run. A failed driver circuit within the PCM can kill an individual coil and prevent that cylinder from firing. But with COP, an individual coil failure will only cause misfiring in one cylinder. It is important to remember that ignition misfire can also be caused by other factors such as worn or fouled spark plugs, loose or damaged coil connectors or terminals, dirty fuel injectors, low fuel pressure, intake vacuum leaks, loss of compression in a cylinder, even a tankful of "bad" gas contaminated with water. These other possibilities should all be ruled out before a COP unit is replaced. The most common trouble codes you may encounter with COP systems on OBD II equipped vehicles are P0300 series codes such as P0301, P0302, etc. that indicate a misfire in a particular cylinder. The important point to remember here is that a general misfire code (P0300) is probably not ignition related but is due to a vacuum leak or fuel delivery problem. A code that indicates a misfire in a single cylinder (such as P0304), on the other hand, will usually be due to a fouled spark plug, weak coil, dirty or dead fuel injector, or loss of compression (burned vale or leaky head gasket). If a misfire is due to a bad coil, you should find a coil code that corresponds to the same cylinder (P0351 to P0358). If a misfire is fuel related, you should also find a code that indicates an open or shorted injector in that cylinder (P0201 to P0208). A COP engine that cranks but fails to start, in many cases, will often have a problem in the crankshaft position sensor circuit (code P0320). Loss of the camshaft position sensor signal (code P0340) may prevent the PCM from properly synchronizing the fuel injectors, but may still allow the engine to start and run in a limp-in mode. On the Chrysler applications, a code P1388 or P1389 would indicate a fault in the auto shutdown relay circuit, while a P1282 would point you toward the fuel pump relay control circuit.
COIL-ON-PLUG IGNITION CHECKS Individual ignition coils can be tested with an ohmmeter the same as those on a conventional distributor or DIS ignition system. Measure primary and secondary resistance and compared to specifications. If resistance is out of specifications, the coil is bad and needs to be replaced. Also, pay close attention to the tube that wraps around the spark plug. Cracks can allow voltage to jump to ground causing a misfire. The spark plug terminal should also fit tightly.
Typical coil-on-plug ignition coil. If a COP coil tests bad and is replaced, future problems can often be avoided by cleaning the COP connector and wiring harness terminals. Corrosion at either place can cause intermittent operation and loss of continuity, which may contribute to component failure. Applying dielectric grease to these connections can help prevent corrosion and assure a good electrical connection. Magnetic crankshaft position sensors can be tested with an ohmmeter, and the sensor output voltage and waveform can be read with an oscilloscope. The output voltage of a Hall Effect crankshaft position sensor can be checked with a voltmeter. On most vehicles, a bad crank position sensor will usually set a fault code which can be read with a scan tool.
SPARK PLUGS
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As for spark plugs, long life platinum plugs are used with most COP ignitions. Such plugs are capable of going 100,000 miles under ideal conditions. But keep in mind any plug can still succumb to fouling and misfire if an engine burns oil, develops an internal coolant leak or runs too rich. Got an Ignition Problem? Need Help Now? Click the Banner Below to Ask an Expert:
More Ignition Articles: Crankshaft Position CKP Sensors Spark Plug Technology Don't Neglect the Spark Plugs Why Spark Plugs Still Need To Be Replaced Ford Motorcraft Spark Plug Breakage Problem (2004 - 2008 Ford Trucks w/5.4L V8, & 2005 - 2008 Mustang GT with 4.6L V8) Analyzing Ignition Misfires Misfire Diagnosis Chrysler 3.5L V6 Engine Won't Start, No Spark Diagnosing An Engine that Won't Crank or Start Spark Plugs & Ignition Performance Spark Plug Wires Distributor Ignition Systems Distributorless Ignition Systems Ignition Coil Diagnosis & Testing
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Troubleshoot Idle Speed Control System
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Troubleshoot Idle Speed Control System Copyright AA1Car The Idle Speed Control (ISC) valve, also called an Idle Air Control (IAC) valve, is used on both throttle body and multipoint fuel injected engines to regulate idle speed. Chrysler calls theirs an Automatic Idle Speed (AIS) motor while Ford refers to theirs as an Idle Speed Control (ISC) solenoid. The IAC valve opens a small bypass circuit that allows air to bypass the throttle. Increasing the volume of air that flows through the bypass circuit around the throttle increases idle speed. Reducing the bypass airflow decreases idle speed. The ISC valve is controlled by the engine's computer (powertrain control module or PCM). The computer monitors idle speed by counting ignition pulses from the ignition module in the distributor or crankshaft position sensor when the throttle position sensor or throttle switch signals the computer that the throttle is closed and the engine is at idle. When the engine's idle speed is above or below the preset range in the computer's program, the computer commands the ISC valve to either increase or decrease the bypass air flow. Additional sensor inputs from the coolant sensor, brake switch and speed sensor may also be used by the computer to regulate idle speed according to various operating conditions. Idle speed may also be increased when the A/C compressor is engaged, the alternator is charging above a certain voltage, and/or the automatic transmission is in gear to prevent the engine from lugging down. DIAGNOSING IDLE SPEED PROBLEMS
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Troubleshoot Idle Speed Control System
If you engine is idling too fast, too slow or stalling, the problem may not be the idle speed control system, but an engine vacuum leak. Check for vacuum leaks first to rule out this possibility. A common condition is to find the idle air bypass solenoid extended all the way out (closed). This usually means the engine has an air leak and the PCM is trying to bring the idle speed back down by closing the idle air bypass circuit. If there is an open or short in the idle air control solenoid, wiring or driver circuit, or the idle speed it out of range, it will usually set one or more fault codes and turn on the Check Engine light. If the light is on, you need to plug a scan tool into the diagnostic connector and read out the codes that set the light.
GENERAL MOTORS IDLE SPEED CONTROL On older pre-OBD II cars, A code 11 indicates a problem in the idle air control circuit. On OBD II vehicles (1996 & newer), codes P505 to P509 indicate a fault with the idle speed control system. The diagnostic procedure involves disconnecting ISC motor, then starting the engine to see if the idle speed increases (it should). Turn the engine off, reconnect IAC and start the engine again. This time the idle speed should return to normal. If it does, the problem is not in the IAC circuit or motor. Check for vacuum leaks or other problems that would affect idle speed. If the idle speed does not change when the IAC is unplugged, and/or does not return to normal after reconnecting the unit, use a test light to check the idle speed control solenoid wiring circuits while the key is on. The test light should flash on and or go from bright to dim on all four circuits if the PCM and wiring are okay (this would tell you teh fault is in the ISC motor). If the test light fails to flash on one or more circuits, the fault is in the wiring or PCM.
FORD IDLE AIR BYPASS Ford doesn't use idle air bypass to regulate idle speed on its older throttle body (CFI) applications, but uses a solenoid or vacuum diaphragm instead to open the throttle linkage. Idle air bypass is used only on multipoint injection applications. On older pre-OBD II cars, codes 12, 13, 16, 17 & 19 all indicate idle speed is out of spec (too high or too low). Codes 47 and 48 indicate a fuel mixture problem which could be caused by an air leak. On OBD II vehicles (1996 & newer), codes P505 to P509 indicate a fault with the idle speed control system. The diagnostic procedure when any of these codes are found is to turn the engine off, unplug the ISC bypass air solenoid connector, then restart the engine to see if the idle rpm drops (it should if the ISC solenoid is working). No change would indicate a problem in the motor or wiring. The ISC solenoid can be checked by measuring its resistance. With the positive lead of a digital volt/ohm meter on the VPWR pin and the negative lead on the ISC pin, measure the resistance of the solenoid. On many applications, the spec calls for 7.0 to 13.0 ohms. If it is out of specs, the ISC solenoid is bad. Also check for shorts between both ISC solenoid
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Troubleshoot Idle Speed Control System
terminals and the case. If the ISC checks out okay, check for battery voltage between the ISC connector terminals while the key is on. Voltage should also vary when the engine is running. No voltage indicates a wiring or computer problem. CHRYSLER IDLE SPEED CONTROL On pre-OBD II Chryslers, a Code 25 means there is a problem in the AIS motor driver circuit. On OBD II vehicles (1996 & newer), codes P505 to P509 indicate a fault with the idle speed control system. The AIS driver circuit can be checked with a bi-directional scan tool using commands to increase idle speed. No change in commanded idle speed would tell you there is a problem in the driver circuit, the wiring or the solenoid. You can remove the AIS from the throttle body to see if the valve pintle is moving in and out, or simply listen for the motor to buzz. In the engine running test mode #70, which checks the throttle body minimum air flow, depressing and holding the proper button on a hand held scan tool should close the AIS bypass circuit. At the same time, ignition timing and fuel mixture are fixed. Idle speed should increase to about 1300 to 1500 rpm. If it doesn't match the specs, the minimum air flow through the throttle body is incorrect. INSTALLING A NEW IDLE SPEED CONTROL SOLENOID When installing a new GM IAC or Chrysler AIS solenoid, the pintle must not extend more than a certain distance from the housing. The specs vary so check the manual or look up the specs in the OEM service literature. Chrysler says one inch (26 mm) is the limit, while some GM allows up to 28 mm on some units and 32 mm on others. If the pintle is overextended, it can be retracted by either pushing it in (GM) or by connecting it to its wiring harness and using actuator test 03 to move it in (Chrysler).
More Fuel System Articles: Finding & Fixing Engine Vacuum Leaks Troubleshoot Hesitation Problems Idle Surge (cause & cure) Fuel System Diagnostics: Finding the Best Approach Diagnosing Returnless Electronic Fuel Injection Systems Troubleshooting & Cleaning Fuel Injectors Throttle-By-Wire systems (Electronic Throttle Control) Bad Gasoline Can Cause Performance Problems Bad Gas Update 2006
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Diagnose Engine Misfire
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Diagnose Engine Misfire Copyright AA1Car Misfire is a common driveability problem that may or may not be easy to diagnose, depending on the cause. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. The loss of 25% of the engine's power output is the equivalent of a horse trying to run on three legs. The engine may shake so badly at idle that it causes vibrations that can be felt in the steering wheel and throughout the vehicle. The engine also may be hard to start and may even stall at idle, depending on the accessory load (air conditioning, headlights and electric rear defroster, for example). When misfire occurs, performance suffers along with fuel economy, emissions and idle quality. And, when a misfiring vehicle is subjected to an emissions test, it will usually fail because of the unusually high levels of hydrocarbons (HC) in the exhaust.
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... ENGINE MISFIRE CODES The Onboard Diagnostic (OBD II) system on 1996 and newer vehicles monitors misfires and will set a Diagnostic Trouble Code (DTC) if the misfire rate exceeds a certain value that may cause emissions to increase. In cases of severe misfire, the Check Engine light may illuminate or flash while the engine is misfiring. The codes can be read by plugging a scan tool into your vehicle's diagnostic connector located under the dash near the steering column. The last two digits in the misfire code will tell you which cylinder or cylinders are misfiring. The digits correspond to the cylinder number in the engine's firing order: P0300....Random P0301....Cylinder P0302....Cylinder P0303....Cylinder P0304....Cylinder P0305....Cylinder
Misfire Code (multiple cylinders involved) 1 Misfire Detected 2 Misfire Detected 3 Misfire Detected 4 Misfire Detected 5 Misfire Detected
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P0306....Cylinder P0307....Cylinder P0308....Cylinder P0309....Cylinder P0310....Cylinder P0311....Cylinder P0312....Cylinder
Diagnose Engine Misfire
6 Misfire Detected 7 Misfire Detected 8 Misfire Detected 9 Misfire Detected 10 Misfire Detected 11 Misfire Detected 12 Misfire Detected
CAUSES OF ENGINE MISFIRE What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression. Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs, bad spark plug wires or even a cracked distributor cap. A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder. "Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator. Low fuel pressure would affect all cylinders rather than an individual cylinder, as would most air leaks. A leaky EGR valve can also have the same effect as an air leak. In fact, if a vehicle has one or more misfire codes and a P0401 EGR code, the fault is likely carbon buildup under the EGR valve. Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit. Intermittent misfires are the worst kind to diagnose because the misfire comes and goes depending on engine load or operating conditions. They seem to occur for no apparent reason. The engine may only misfire and run rough when cold but then smooth out as it warms up. Or, it may start and idle fine but then misfire or hesitate when it comes under load. Also, it may run fine most of the time but suddenly misfire or cut out for no apparent reason.
Engine misfire can be felt at idle as a shak ing or vibration. At higher engine speeds, the engine may cutout, stumble or lose power. MISFIRE DIAGNOSIS WITH A SCAN TOOL If you find one or more misfire codes when you check for fault codes with a scan tool, the codes by themselves do NOT tell you WHY the cylinder is misfiring. It could be ignition, compression or fuel related. However, if you find a P0304 misfire code for cylinder number 4, and also a P0204 code (P0200 series codes cover the injectors), you'd know the misfire was probably caused by a bad injector. If there are any EGR codes (P0401 for example), the misfire could be due to carbon buildup under the EGR valve. If there is a lean code (P0171 or P0174), the problem could be a dirty fuel injector. If there are no other codes except for the misfire code, check the ignition components for that cylinder. The cause could be a badly worn or fouled spark plug, a bad plug wire, carbon tracking or moisture inside the boot of a coil-on-plug ignition coil, or a weak or defective coil in a multi-coil distributorless ignition system. If you find a P0300 random misfire code, it means the misfire is random and is moving around from cylinder to cylinder. The cause here would likely be something that upsets the engine's air/fuel mixture, such as a major vacuum leak, a leaky EGR valve or unusually low fuel pressure (weak pump or faulty pressure regulator). If your engine seems to be misfiring, but there are NO codes set (no individual cylinder misfire codes or no random misfire code), and you have a professional grade scan tool that can access Mode $06 data, you can use the scan tool to look at the raw misfire data that is being tabulated for each cylinder. Normally the misfire counts should be zero or close to zero for every cylinder. The OBD II system will usually NOT set a misfire code until the actual misfire count exceeds about two percent for any given cylinder. So by looking at the actual Mode $06 misfire data, you should be able to see any cylinders
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that are showing an abnormally high misfire rate. For example, if the Mode $06 scan tool data shows zero or close to zero misfires for all cylinders except cylinder number four (which has a count of say 80 or higher), that would tell you cylinder number four has an ignition, fuel or compression problem that will require further diagnosis. FINDING THE CAUSE OF A STEADY OR CONTINUOUS MISFIRE In the case of a steady misfire, isolating the misfiring cylinder is the first step in diagnosing the problem. The old-fashioned method for finding a weak cylinder is to temporarily disconnect each of the spark plug wires, one at a time, while the engine is idling. When there's no change in the idle speed, then you have pinpointed the weak cylinder. A power balance test will tell you the same thing, but this requires some hookups and an engine analyzer. A power balance test is preferable to pulling plug wires, because it keeps you away from the voltage and prevents the voltage from causing any damage to the electronics in the ignition system. When a plug wire is physically disconnected from a spark plug, the high voltage surge from the coil cannot follow its normal path to ground through the plug wire and spark plug, so it passes back through the coil. Most ignition systems are robust enough to withstand such voltage backups intermittently but not on a prolonged basis. If the coil or ignition module is already weak, it may push the component over the brink causing it to fail. ADVANCED MISFIRE DIAGNOSTICS WITH A DIGITAL STORAGE OSCILLOSCOPE A weak cylinder will stick out like a sore thumb on an ignition scope or a digital storage oscilloscope (DSO). The secondary parade pattern will reveal the firing voltages for each cylinder. The number one cylinder will be the first one on the display, followed by each of the other cylinders in their respective firing order, moving across the screen from left to right. If the peak firing voltage for any cylinder is significantly higher or lower than the others, it indicates a problem. An usually low firing voltage would tell you the spark is finding a shortcut to ground. A fouled, shorted or cracked spark plug; arcing past the spark plug boot to ground; and a shorted plug wire would be the most likely causes. An unusually high firing voltage in a cylinder would tell you the spark plug electrode is too wide or too badly worn or that the plug wire is open.
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If the firing voltages for all the cylinders are about equal with the engine idling, a snap-kV test will help you find a misfire that occurs when the engine is under load. To conduct this test, suddenly open the throttle wide and then let it fall back while observing the firing pattern on the scope. All the firing voltages should increase during the snap-kV acceleration test, but, if any individual cylinder increases significantly more or less than its companions, it indicates trouble. A snap-kV voltage spike that is taller than the rest indicates high resistance in the ignition secondary to the affected cylinder. Check for excessive resistance or an open in the plug wire. A spike that is much shorter than the rest indicates loss of voltage. Check for a shorted, cracked or damaged spark plug, arcing across the spark plug boot or a shorted plug wire. Misfire under load accompanied by low overall spike heights during the snap-kV test would tell you the available voltage from the coil is low. The most likely cause, in this case, would be a faulty ignition coil. But low battery voltage might also be a factor, too. Be sure to check the battery and charging voltage.
The next thing you should look at is the primary pattern for the suspicious cylinder. The primary pattern can reveal additional pieces in the diagnostic puzzle. The primary pattern will show when the coil starts to charge, the peak or "arc-over" firing voltage (which you've already looked at and determined was higher or lower than normal), the "spark burn line" and coil oscillations. The spark burn line is the part of the waveform that immediately follows the firing voltage spike. The height of this line can tell you if the air/fuel mixture is running rich or lean. If the fuel mixture is lean, then the spark burn line will be higher than normal. If the air/fuel mixture is rich, then the spark burn line will be lower than normal. A lean mixture in a single cylinder can be caused by a leaky intake manifold gasket, air leakage past injector O-rings, a leaky EGR valve (if the valve is adjacent to the cylinder intake port) or a dirty, plugged or inoperative fuel injector. Loss of compression because of a leaky (burned) exhaust valve or a leaky head gasket can also affect the spark burn line in the
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Diagnose Engine Misfire
same way. Note: If the spark burn lines for all the cylinders are higher than normal (indicating a lean fuel mixture), the underlying cause would be something that affects all cylinders such as an intake manifold vacuum leak, leaky vacuum hose, leaky EGR valve, leaky throttle gasket or low fuel pressure (weak fuel pump or bad pressure regulator). A rich fuel mixture in an individual cylinder is less common but can occur if the fuel injector leaks. A more common condition would be a rich condition in all cylinders caused by a dead oxygen sensor or coolant sensor that prevents the computer from going into closed loop, or by a faulty fuel pressure regulator that feeds too much pressure to the injectors. Something else to look at in the spark burn line is the amount of "hash" it contains. A good cylinder will show a relatively clean line with little hash. A lot of hash, on the other hand, occurs when ignition misfire or lean misfire are present. The duration or length of the spark burn line can provide more clues about what's going on inside the cylinder. If the duration of the burn line is longer than about 2 milliseconds, the air/fuel mixture is running abnormally rich for any of the reasons just given. If the burn line is shorter than about 0/75 milliseconds, then the cylinder is running too lean. The last thing you want to look at in the primary ignition pattern is coil oscillations. If the coil is good, there should be at least two and preferably three or more oscillations after the burn line. Fewer oscillations would indicate a faulty coil. IGNITION AND COMPRESSION CHECKS If you have a misfire and have isolated it to one cylinder, the cause will be obvious when you remove the spark plug. If the plug's insulator is cracked or broken, you've found the problem. If the plug appears to be OK but is wet, inspect the plug wire and boots for damage. Measure the plug wire's resistance, end to end, with an ohmmeter. Refer to the vehicle manufacturer's specifications, but, as a rule, resistance should not exceed 8,000 ohms per foot. Replace the wire if resistance exceeds specifications. If the plug is fouled, you've found the source of the misfire, but you still have to determine what caused the plug to foul. Heavy black oily carbon deposits would tell you that the engine is burning oil. The most likely cause is worn valve guide seals and/or guides, but worn rings and cylinders can also allow oil to enter the combustion chamber. Replacing the spark plug will temporarily cure your customer's misfire problem, but, until the oil consumption problem is fixed, the engine will continue to foul plugs. A leakdown test or compression test will help you determine if the oil is getting past the valve guides or the rings. If the cylinder shows little leakdown or holds good compression when a little oil is squirted into the cylinder (wet compression test), it would tell you that the engine needs new valve guide seals and/or guide work. Most late model engines have positive valve guide seals. Often, the guides are fine, but the seals are worn or cracked. The seals can be replaced on some engines without too much effort and without having to remove the head. Just pull off the valve cover, remove the valvetrain hardware and use an external spring compressor to remove the springs so new seals can be installed. A regulated air hose connected to the spark plug hole will keep the valve from dropping into the cylinder. But, on many OHC engines, there's so much disassembly involved to get to the valve springs you may have to remove the head. A spark plug that shows heavy whitish to brown deposits may indicate a coolant leak either past the head gasket or through a crack in the combustion chamber. This type of problem will only get worse and may soon lead to even greater problems if the leak isn't fixed. Coolant makes a lousy lubricant and can cause ring, cylinder and bearing damage if it gets into a cylinder or the crankcase. Loss of coolant can also lead to overheating, which may result in cracking or warping of aluminum cylinder heads. If you suspect this kind of problem, pressure test the cooling system to check for internal coolant leakage. Spark plugs that show preignition or detonation damage may indicate a need to check timing, the operation of the cooling system and conditions that cause a lean air/fuel mixture. You might also want to switch to a colder heat range plug. Short trip stop-and-go driving can cause a rapid buildup of normal deposits on plugs, especially if the engine has a lot of miles and there has been some oil leakage past the valve guide seals and rings. The cure here might be to switch to a onestep hotter spark plug. If the spark plug and plug wire are OK but the cylinder is weak, a leakdown or compression test should be done to determine if the problem is compression related. The exhaust valves are the ones most likely to lose their seal and leak compression, so, if you find unusually low compression, follow up with a wet compression test to determine if the problem lies with the valves or rings.
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No change in compression with a wet test would tell you the problem is valve related (probably a bad exhaust valve) or a blown head gasket. But, if the compression readings are significantly higher with a wet compression test, it would tell you the piston rings and/or cylinder walls are worn. Either way, your customer is looking at major repairs. The only cure for a leaky valve is a valve job, and the only cure for a leaky head gasket is to replace the gasket. Likewise, the only cure for worn rings and cylinders is to overhaul or replace the engine. Low compression can also be caused by a rounded cam lobe. If the valve doesn't open, the cylinder can't breathe normally and compression will be low. A visual inspection of the valvetrain and cam will be necessary if you suspect this kind of problem.
A dirty fuel injector or fouled spark plug can cause misfires. FUEL INJECTOR CHECKS If the ignition components and compression in a misfiring cylinder are fine, that leaves a fuel-related problem as the only other possibility. You can start by checking for voltage at the injector. A good injector should also buzz while the engine is running. No buzzing would tell you the injector is dead, while a no-voltage reading would tell you it isn't the injector's fault but a wiring or computer driver problem. If the injector is buzzing and spraying fuel but the cylinder isn't getting enough fuel, the injector is dirty or clogged. On-car cleaning may help remove the varnish deposits that are restricting the injector and restricting fuel delivery, but chances are, if the injector is clogged enough to cause a steady misfire, it will have to be removed for off-car cleaning or be replaced. You can also observe injector performance on a scope, and check its response to changes in the air/fuel mixture. First of all, a flat line would tell you the injector is dead or is not receiving voltage (depending on where the line falls on the screen). If the injector is working, the line should drop when the injector turns on, then peak when the current is switched off. The injector scope pattern will tell you how long the injector is on. If you make the air/fuel mixture artificially lean by momentarily pulling off a vacuum hose, and/or artificially rich by feeding some propane into the manifold, you should see a corresponding change in the injector on time as the computer responds to input from the oxygen sensor. No change would tell you either the O2 sensor is dead or there's a problem in the computer. One thing that should always be checked if an injector is removed for cleaning and/or testing is its spray pattern. A good injector should produce a cone-shaped mist of fuel vapor. If you see solid streamers in the spray pattern or a solid stream of fuel, the injector needs attention. If off-car cleaning fails to restore the normal spray pattern, the injector must be replaced. If you're dealing with a random misfire that can't be isolated to a particular cylinder, all the injectors may be dirty. You should also check fuel pressure to see if the pump is weak or the pressure regulator is defective. A plugged fuel filter can reduce fuel pressure. If fuel pressure is within specifications, check the intake vacuum to see if there is an air leak that's upsetting the overall air/fuel mixture. A couple of overlooked causes here may be a leaky EGR valve or a leaky power brake booster. Share
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Problem Idle Surge
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Problem: Idle Surge Copyright AA1Car If a vehicle idles erratically and surges (idle speed is not steady and increases and decreases), the problem may be a buildup of carbon or fuel varnish deposits in the idle speed control valve (also called the idle air control valve or IAC valve). The cure for this condition is to clean the valve with some aerosol throttle cleaner or engine top cleaner. Here's how to clean the IAC valve: Disconnect the air intake ductwork from the throttle body. Start the engine, then increase and hold the idle speed to 1,000 to 1,500 rpm. Spray the throttle cleaner or engine cleaner into the throat of the throttle body, aiming for the idle air bypass port (usually located on the side or top of the throttle body opening). Give this area a good dose of cleaner (about 10 second's worth). Turn the engine off to allow the cleaner to soak into the IAC passageway. Wait about three minutes. Restart the engine, rev and hold at 1,000 to 1,500 rpm, and repeat the cleaning process again. Turn the engine off again, and reattach the air intake duct work to the throttle body. Start the engine and rev and hold to 1,500 to 2,000 rpm until no white smoke is coming out of the exhaust pipe.
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Problem Idle Surge
Cleaning the Idle Air Speed Control Valve with aerosol throttle cleaner can often solve an idle problem. If this fails to make any difference, you can remove the IAC valve from the throttle body and spray cleaner directly on the tip of the valve and/or into the ports in the throttle body. Let the cleaner soak awhile, repeat as needed, then reinstall the IAC valve, start the engine and run it at 1,500 to 2,000 rpm as before until no white smoke is seen in the exahust. If the idle speed still surges after this, the IAC valve is defective and needs to be replaced.
If the old Idle Speed Control Valve fails to respond to cleaning, replace it with a new one.
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Related Articles: Troubleshooting Idle Speed Control System Mass Airflow MAF Sensors Troubleshooting & Cleaning Fuel Injectors Bad Gasoline Can Cause Performance Problems More on Problems Caused by Bad Gas Finding & Fixing Engine Vacuum Leaks Got an Idle Surge Problem? Need Help Now? Click the Banner Below to Ask an Expert:
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How to Diagnose and Test an Ignition Coil
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How to Diagnose and Test an Ignition Coil Copyright AA1Car.com Ignition coils provide the high voltage needed by the ignition system to fire the spark plugs. Most engines that have a distributor ignition system have a single coil, but a few import applications have two coils. On distributorless ignition systems (DIS), multiple ignition coils are used. On "waste spark" systems, each pair of cylinders shares a coil. On other DIS and coilon-plug (COP) ignition systems, each cylinder or spark plug has its own individual coil. The ignition coil serves as a high voltage transformer. It steps up the ignition system's primary voltage from 12 volts up to thousands of volts. The actual firing voltage needed to create a spark across a spark plug's electrode gap depends on the width of the gap, the electrical resistance in the spark plug and plug wires, the air/fuel mixture, the load on the engine and the temperature of the spark plug. The voltage required is constantly changing and can vary from as little as 5,000 volts up to 25,000 volts or more. Some systems can put out as much as 40,000 volts under peak demand. HOW AN IGNITION COIL WORKS Inside every ignition coil are two sets of windings around a laminated or segmented iron core. The "primary" windings, which number a few hundred, are connected to the two external low voltage terminals on the coil. The positive (+) primary terminal connects to the ignition switch and battery while the negative (-) primary terminal connects to the ignition module which provides ground. The "secondary" windings, which have thousands of turns, are connected at one end to the primary positive terminal and the high voltage secondary output terminal in the center of the coil at the other end. The ratio of secondary to primary windings is typically around 80 to one. The higher the ratio, the higher the potential output voltage of the coil. Performance ignition coils typically have a higher ratio than standard coils. When the ignition module closes the coil primary circuit and provides a ground, current flows through the primary windings. This creates a strong magnetic field around the iron core and charges up the coil. It takes about 10 to 15 milliseconds for the magnetic field to reach maximum strength. The ignition module then opens the coil's ground connection and turns the primary coil windings off. This causes the magnetic field to suddenly collapse. The energy stored in the magnetic field has to go somewhere so it induces a current in the coil's secondary windings. Depending on the ratio of turns of wire, this multiplies the voltage up to 100 times or more until there is enough voltage to fire the spark plug.
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How to Diagnose and Test an Ignition Coil
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. IGNITION COIL FAILURES Ignition coils are very rugged and reliable, but can fail for a variety of reasons. Heat and vibration can damage the coil's windings and insulation causing shorts or opens in the primary or secondary windings. But the number one killer of ignition coils is voltage overload caused by bad spark plugs or plug wires. If a spark plug or plug wire is open or has excessive resistance, the ignition coil's output voltage can rise to the point where it burns through the coil's internal insulation causing a short. The insulation in many coils can be damaged if output exceeds 35,000 volts. Once this happens, the coil's output voltage may drop causing ignition misfire when the engine is under load, or the coil may cease to put out any voltage preventing the engine from starting or running. If a coil has battery voltage at its positive terminal and is being grounded on and off by the ignition module or circuit but is not producing a spark, the coil is defective and needs to be replaced. TIP: If the ignition module has failed more than once, it may be due to a bad ignition coil. Internal arcing or shorts in a coil can overload and damage the circuitry inside the ignition module. IGNITION COIL DIAGNOSIS When a coil failure occurs on a distributor ignition system, it affects all the cylinders. The engine may not start or it may misfire badly when under load. The misfire may also jump from cylinder to cylinder. But on an engine with a distributorless ignition system (DIS) or coil-on-plug (COP) ignition system, a single coil failure will only affect one cylinder (or two cylinders if it is a DIS waste spark system where two cylinders that are opposite each other in the firing order share the same coil). If your engine is running rough (misfiring) and the Check Engine Light is on, use a code reader or scan tool to check for misfire codes. On 1996 and newer engines with OBD II and misfire detection, a coil failure will usually set a P030X misfire code where "X" is the number of the cylinder that is misfiring. A misfire code P0301, for example, would tell you cylinder #1 is misfiring. But a misfire code can be caused by an ignition problem, a fuel problem or a compression problem, so don't jump to conclusions as assume a misfire means a bad coil, spark plug or plug wire. It could also be a bad injector or a compression leak (bent or burned valve). If the coil is shorted or open, a code may also be set for the coil on that cylinder. If there is no code, you should measure the coil's primary and secondary resistance with a digital ohmmeter. You should also remove and inspect the spark plug. Check the spark gap and look at the deposits on the plug to see if the misfire is due to carbon or oil buildup. Also check the plug wire (if there is one) to make sure the wire's resistance is within specifications. If the coil, spark plug and plug wire all appear to be okay, the misfire may be due to a dirty or dead fuel injector (check the injector's resistance and voltage supply, and use a NOID light to check for a pulse from the PCM driver circuit. If the injector appears to be okay, do a compression check to see if the cylinder has a bad valve or leaky head gasket. NOTE: If an engine with a COP ignition system cranks normally but won't start because there is no spark, the problem is not one or more bad coils. More likely, the fault is a bad crankshaft or camshaft position sensor, a voltage supply problem to the coils in the ignition circuit, a bad ignition module (if used), or a bad ignition coil driver circuit in the PCM.
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How to Diagnose and Test an Ignition Coil
Cutaway of coil-on-plug ignition on a Cadillac Northstar engine. HOW TO TEST AN IGNITION COIL WARNING: Never pull off a plug wire or the coil's high voltage output wire to test for a spark. Besides risking a severe shock, an open plug wire or coil wire will increase the voltage demands on the coil to the point where it may damage the coil. The only safe way to test for spark is to use a spark plug tester tool. If a coil problem is suspected, measure the coil's primary and secondary resistance with an ohmmeter. If either is out of specifications, the coil needs to be replaced. A coil can be easily bench tested with a digital 10 megaohm impedance ohmmeter. Refer to the vehicle manufacturers service information for the coil test specifications because the values can vary depending on the application.
To test the ignition coil connect the ohmmeter's two test leads to the coils primary terminals (+ and -). Most coils should read between 0.4 and 2 ohms. Zero resistance would indicate a shorted coil while a high resistance reading would indicate an open coil. Secondary resistance is measured between the positive (+) terminal and high voltage output terminal. Newer coils with segmented core construction typically read 6,000 to 8,000 ohms, while others can may read as high as 15,000 ohms. On coils that are not a can style, the primary terminals may be located in a connector or even under the coil. Refer to the vehicle manufacturer's service information for the terminal locations and ignition coil test procedures.
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How to Diagnose and Test an Ignition Coil
Ford DIS V6 ignition coil. Note terminals are in coil wiring conenctor. A BAD COIL CAN DAMAGE THE PCM A short that lowers normal resistance in the primary windings will allow excessive current to flow through the coil, which may damage the PCM driver circuit. This may also reduce the coil's voltage output resulting in a weak spark, hard starting, hesitation or misfire under load or when accelerating. Abnormally high resistance or an open circuit in a coil's primary windings will not usually damage the PCM driver circuit, but it will reduce the coil's secondary voltage output or kill it altogether. A short that reduces resistance in a coil's secondary windings will also result in a weak spark, but will not damage the PCM driver circuit. An open or higher than normal resistance in a coil's secondary windings will also cause a weak spark or no spark, and may also damage the PCM driver circuit due to feedback induction through the primary circuit. REPLACE IGNITION COIL A replacement coil should be the same as the original (unless you are upgrading the ignition system with a higher output performance coil). When replacing the coil, the connectors should be cleaned and checked for corrosion or looseness to assure a good electrical connection. Corrosion can cause resistance, intermittent operation, or loss of continuity, which may contribute to component failure. Applying dielectric grease to coil connectors that fit over the spark plugs is also recommended to minimize the risk of spark flashover caused by moisture. On Ford truck engiens with COP ignition coils, moisture contamination that causes corrosion is the number one cause of coil failure. If an engine is experiencing repeated coil failures, the coils may be working too hard. The underlying cause may be high secondary resistance (worn spark plugs or excessive spark plug gap), or in rare cases a lean fuel condition (dirty injectors, vacuum leak or leaky EGR valve). On high mileage engines with COP ignitions, new plugs should also be installed if a coil has failed if the original plugs are conventional plugs with more than 45,000 miles on them, or long-life platinum or iridium plugs with more than 100,000 miles on them.
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Engine Won't Crank or Start
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Engine Won't Crank or Start Copyright AA1Car
What To Do When Your Car Won't Start Every engine requires four basic ingredients to start: sufficient cranking speed, good compression, adequate ignition voltage (with correct timing) and fuel (a relatively rich air/fuel mixture initially). So if your car fails to start, you can assume it lacks one of these four essential ingredients. But which one? To find you, you need to analyze the situation. If the engine won't crank, you are probably dealing with a starter or battery problem. Has the starter been acting up? (unusual noises, slow cranking, etc.). Is this the first time the engine has failed to crank or start, or has it happened before? Have the starter, battery or battery cables been replaced recently? Might be a defective part. Has the battery been running down? Might be a charging problem. Have there been any other electrical problems? The answers to these questions should shed some light on what might be causing the problem. If an engine cranks but refuses to start, it lacks ignition, fuel or compression. Was it running fine but quit suddenly? The most likely causes here would be a failed fuel pump, ignition module or broken overhead cam timing belt. Has the engine been getting progressively harder to start? If yes, consider the engine's maintenance and repair history.
NO START DIAGNOSIS What happens when you attempt to start the engine? If nothing happens when you turn the key, check the battery to determine its state of charge. Many starters won't do a thing unless there is at least 10 volts available from the battery. A low battery does not necessarily mean the battery is the problem, though. The battery may have been run down by prolonged cranking while trying to start the engine. Or, the battery's low state of charge may be the result of a charging system problem. Either way, the battery needs to be recharged and tested. http://www.aa1car.com/library/us1296.htm
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Engine Won't Crank or Start
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If the battery is low, the next logical step might be to try starting the engine with another battery or a charger. If the engine cranks normally and roars to life, you can assume the problem was a dead battery, or a charging problem that allowed the battery to run down. If the battery accepts a charge and tests okay, checking the output of the charging system should help you identify any problems there. A charging system that is working properly should produce a charging voltage of somewhere around 14 volts at idle with the lights and accessories off. When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, then taper off, leveling out at the specified voltage. The exact charging voltage will vary according to the battery's state of charge, the load on the electrical system, and temperature. The lower the temperature, the higher the charging voltage. The higher the temperature, the lower the charging voltage. The charging range for a typical alternator might be 13.9 to 14.4 volts at 80 degrees F, but increase to 14.9 to 15.8 volts at
subzero temperatures. If the charging system is not putting out the required voltage, is it the alternator or the regulator? Full fielding the alternator to bypass the regulator should tell you if it is working correctly. Or, take the alternator to a parts store and have it bench tested. If the charging voltage goes up when the regulator is bypassed, the problem is the regulator (or the engine computer in the case of computer-regulated systems). If there is no change in output voltage, the alternator is the culprit. Many times one or more diodes in the alternator rectifier assembly will have failed, causing a drop in the unit's output. The alternator will still produce current, but not enough to keep the battery fully charged. This type of failure will show up on an oscilloscope as one or more missing humps in the alternator waveform. Most charging system analyzers can detect this type of problem.
ENGINE CRANKING PROBLEMS If your car won't start because the engine won't crank or cranks slowly (and the battery is fully charged), you can focus your attention on the starter circuit. A quick way to diagnose cranking problems is to switch on the headlights and watch what happens when you attempt to start the engine. If the headlights go out, a poor battery cable connection may be strangling the flow of amps. All battery cable connections should be checked and cleaned along with the engine-to-chassis ground straps. Measuring the voltage dropacross connections is a good way to find excessive resistance. A voltmeter check of the cable connections should show no more than 0.1 volt drop at any point, and no more than 0.4 volts for the entire starter circuit. A higher voltage drop would indicate excessive resistance and a need for cleaning or tightening. Slow cranking can also be caused by undersized battery cables. Some cheap replacement cables have small gauge wire encased in thick insulation. The cables look the same size as the originals on the outside, but inside there is not enough wire to handle the amps. If the headlights continue to shine brightly when you attempt to start the engine and nothing happens (no cranking), voltage is not reaching the starter. The problem here is likely an open or misadjusted park/neutral safety switch, a bad ignition switch, or a faulty starter relay or solenoid. Fuses and fusible links should also be checked because overloads caused by continuous cranking or jump starting may have blown one of these protective devices.
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If the starter or solenoid clicks but nothing else happens when you attempt to start the engine, there may not be enough amps to spin the starter. Or the starter may be bad. A poor battery cable, solenoid or ground connection, or high resistance in the solenoid itself may be the problem. A voltage check at the solenoid will reveal if battery voltage is passing through the ignition switch circuit. If the solenoid or relay is receiving battery voltage but is not closing or passing enough amps from the battery to spin the starter motor, the solenoid ground may be bad or the contacts in the solenoid may be worn, pitted or corroded. If the starter cranks when the solenoid is bypassed, a new solenoid is needed, not a starter. Most engines need a cranking speed of 200 to 300 rpm for your car to start, so if the starter is weak and can't crank the engine fast enough to build compression, the engine won't start. In some instances, a weak starter may crank the engine fast enough but prevent it from starting because it draws all the power from the battery and does not leave enough for the injectors or ignition system. If the lights dim and there is little or no cranking when you attempt to start the engine, the starter may be locked up, dragging or suffering from high internal resistance, worn brushes, shorts or opens in the windings or armature. A starter current draw test will tell you if the starter is pulling too many amps. A good starter will normally draw 60 to 150 amps with no load on it, and up to 200 amps or more while cranking the engine. The no load amp draw depends on the rating of the starter while the cranking amp draw depends on the displacement and compression of the engine. Always refer to the OEM specs for the exact amp values. Some "high torque" GM starters, for example, may have a no load draw of up to 250 amps. Toyota starters on four-cylinder engines typically draw 130 to 150 amps, and up to 175 amps on six-cylinder engines. An unusually high current draw and low free turning speed or cranking speed typically indicates a shorted armature, grounded armature or field coils, or excessive friction within the starter itself (dirty, worn or binding bearings or bushings, a bent armature shaft or contact between the armature and field coils). The magnets in permanent magnet starters can sometimes break or separate from the housing and drag against the armature. A starter that does not turn at all and draws a high current may have a ground in the terminal or field coils, or a frozen armature. On the other hand, the start may be fine but can't crank the engine because the engine is seized or hydrolocked. So before you condemn the starter, try turning the engine over by hand. Won't budge? Then the engine is probably locked up. A starter that won't spin at all and draws zero amps has an open field circuit, open armature coils, defective brushes or a defective solenoid. Low free turning speed combined with a low current draw indicates high internal resistance (bad connections, bad brushes, open field coils or armature windings). If the starter motor spins but fails to engage the flywheel, the cause may be a weak solenoid, defective starter drive or broken teeth on the flywheel. A starter drive that is on the verge of failure may engage briefly but then slip. Pull the starter and inspect the drive. It should turn freely in one direction but not in the other. A bad drive will turn freely in both directions or not at all.
ENGINE CRANKS BUT YOUR CAR WILL NOT START
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When the engine cranks normally but you car won't start, you need to check ignition, fuel and compression. Ignition is easy enough to check with a spark tester or by positioning a plug wire near a good ground. No spark? The most likely causes would be a failed ignition module, distributor pickup or crankshaft position (CKP) sensor. A tool such as an Ignition System Simulator can speed the diagnosis by quickly telling you if the ignition module and coil are capable of producing a spark with a simulated timing input signal. If the simulated signal generates a spark, the problem is a bad distributor pickup or crankshaft position sensor. No spark would point to a bad module or coil. Measuring ignition coil primary and secondary resistance can rule out that component as the culprit.
Module problems as well as pickup problems are often caused by loose, broken or corroded wiring terminals and connectors. Older GM HEI ignition modules are notorious for this. If you are working on a distributorless ignition system with a Hall effect crankshaft position sensor, check the sensor's reference voltage (VRef) and ground. The sensor must have 5 volts or it will remain permanently off and not generate a crank signal (which should set a fault code). Measure VRef between the sensor power supply wire and ground (use the engine block for a ground, not the sensor ground circuit wire). Don't see 5 volts? Then check the sensor wiring harness for loose or corroded connectors. A poor
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Engine Won't Crank or Start
ground connection will have the same effect on the sensor operation as a bad VRef supply. Measure the voltage drop between the sensor ground wire and the engine block. More than a 0.1 voltage drop indicates a bad ground connection. Check the sensor mounting and wiring harness. If a Hall effect crank sensor has power and ground, the next thing to check would be its output. With nothing in the sensor window, the sensor should be "on" and read 5 volts (VRef). Measure the sensor D.C. output voltage between the sensor signal output wire and ground (use the engine block again, not the ground wire). When the engine is cranked, the sensor output should drop to zero every time the shutter blade, notch, magnetic button or gear tooth passes through the sensor. No change in voltage would indicate a bad sensor that needs to be replaced. If the primary side of the ignition system seems to be producing a trigger signal for the coil but the voltage is not reaching the plugs, a visual inspection of the coil tower, distributor cap, rotor and plug wires should be made to identify any defects that might be preventing the spark from reaching its intended destination.
ENGINE CRANKS, HAS SPARK BUT WILL NOT START If you see a good hot spark when you crank the engine, but it won't start, check for fuel. The problem might be a bad fuel pump. On an older engine with a carburetor, pump the throttle linkage and look for fuel squirting into the carburetor throat. No fuel? Possible causes include a bad mechanical fuel pump, stuck needle valve in the carburetor, a plugged fuel line or fuel filter. On newer vehicles with electronic fuel injection, connect a pressure gauge to the fuel rail to see if there is any pressure in the line. No pressure when the key is on? Check for a failed fuel pump, pump relay, fuse or wiring problem. On Fords, don't forget to check the inertia safety switch which is usually hidden in the trunk or under a rear kick panel. The switch shuts off the fuel pump in an accident. So if the switch has been tripped, resetting it should restore the flow of fuel to the engine. Lack of fuel can also be caused by obstructions in the fuel line or pickup sock inside the tank. And don't forget to check the fuel gauge. It is amazing how many no starts are caused by an empty fuel tank. There is also the possibility that the fuel in the tank may be heavily contaminated with water or overloaded with alcohol. If the tank was just filled, bad gas might be causing the problem. On EFI-equipped engines, fuel pressure in the line does not necessarily mean the fuel is being injected into the engine. Listen for clicking or buzzing that would indicate the injectors are working. No noise? Check for voltage and ground at the injectors. A defective ECM may not be driving the injectors, or the EFI power supply relay may have called it quits. Some EFI-systems rely on input from the camshaft position sensor to generate the injector pulses. Loss of this signal could prevent the system from functioning. Even if there is fuel and it is being delivered to the engine, a massive vacuum leak could be preventing the engine from starting. A large enough vacuum leak will lean out the air/fuel ratio to such an extent that the mixture won't ignite. An EGR valve that is stuck wide open, a disconnected PCV hose, loose vacuum hose for the power brake booster, or similar leak could be the culprit. Check all vacuum connections and listen for unusual sucking noises while cranking.
ENGINE HAS FUEL AND SPARK BUT WILL NOT START An engine that has fuel and spark, no serious vacuum leaks and cranks normally should start. The problem is compression . If it is an overhead cam engine with a rubber timing belt, a broken timing belt would be the most likely cause especially if the engine has a lot of miles on it. Most OEMs recommend replacing the OHC timing belt every 60,000 miles for preventative maintenance, but many belts are never changed. Eventually they break, and when they do the engine stops dead in its tracks. And in engines that lack sufficient valve-to-piston clearance as many import engines and some domestic engines do, it also causes extensive damage (bent valves and valvetrain components & sometimes cracked pistons). Overhead cams can also bind and break if the head warps due to severe overheating, or the cam bearings are starved for lubrication. A cam seizure may occur during a subzero cold start if the oil in the crankcase is too thick and is slow to reach the cam (a good reason for using 5W-20 or 5W-30 for winter driving). High rpm cam failure can occur if the oil level is low or the oil is long overdue for a change. With high mileage pushrod engines, the timing chain may have broken or slipped. Either type of problem can be diagnosed by doing a compression check and/or removing a valve cover and watching for valve movement when the engine is cranked. A blown head gasket may prevent an engine from starting if the engine is a four cylinder with two dead cylinders. But most six or eight cylinder engines will sputter to life and run roughly even with a blown gasket. The gasket can, however, allow coolant to leak into the cylinder and hydrolock the engine.
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Troubleshoot Engine with Infrared Thermometer
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Troubleshoot Engine With Infrared Thermometer Copyright AA1Car Before you can fix a cooling problem, you first have to diagnose the underlying cause, which is often the most timeconsuming and challenging part of the job. One way to speed up the process is to use temperature checks to zero in on critical components. Overheating, as you know, can have many possible causes: a stuck thermostat, a clogged radiator, a cooling fan that is not coming on, low coolant, etc. By a process of elimination, you can eventually figure out what is causing a problem. But how long will it take you? And will you be absolutely sure of your diagnosis before you replace any parts? The "old fashioned" way of checking a thermostat is to remove it from the engine so it can be dipped into a bucket of hot water to see if it opens. Most technicians do not have that kind of time to waste so they simply replace the thermostat if they have reason to suspect it might not be working properly. Sometimes they are right and sometimes they are not. A better way of testing a thermostat is to measure the actual temperature at which it opens on the engine, not in a bucket. That way, if the thermostat is good you have not wasted valuable time replacing it unnecessarily. You can proceed to other diagnostic checks or repairs.
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Troubleshoot Engine with Infrared Thermometer
Aiming your infrared thermometer at the upper radiator hose will tell if if the thermostat is open or closed. A low temperature reading means no coolant flow through the upper radiator hose.
INFRARED THERMOMETER A good way to do this is with a noncontact infrared thermometer such as Raytek's Raynger ST that measures heat energy radiating from the thermostat housing. An ordinary contact thermometer relies on surface conductivity to take a temperature reading. Consequently, it is slow and may not give an accurate measurement if there is poor contact between the thermometer and thermostat housing. But a noncontact infrared thermometer does not rely on direct physical contact. It measures infrared heat energy radiated from the thermostat housing and gives you instant results. Note: The accuracy of an infrared temperature reading depends on the reflectivity (emissivity) of the surface. The Raytek Raynger ST accurately measures surface temperatures from -25 degrees F all the way up to 750 degrees F with an accuracy of plus or minus one percent! All you do is point the pistol-shaped Raynger ST at the surface to be measured and pull the trigger. It is that easy. There is even a built-in laser pointer on some models to help you aim at the spot you want to measure. Using a noncontact infrared thermometer also eliminates the danger of coming into contact with hot surfaces, high voltage plug wires or moving parts such as fans, belts or pulleys.
USE INFRARED THERMOMETER TO MAKE TEMPERATURE CHECKS
Temperature Calibration Solutions from Primary Laboratories to Industrial Temperature Sensors
To check the opening temperature of the thermostat, aim your infrared thermometer at the thermostat housing as the engine warms up. The thermostat housing will rise in temperature as the engine heats up. When the thermostat opens, the temperature will level off. If the thermostat checks out okay, make sure the cooling fan is coming on when the coolant temperature reaches 220 to 240 degrees F. No fan would tell you there is a problem with the fan motor, wiring harness, relay or coolant temperature switch. If the fan is working properly but the engine is still running hot, scan the entire surface of the radiator to check for clogs. Temperature readings should decrease evenly from one side to the other on a crossflow radiator, or from top to bottom on a downflow radiator. If you find an area where there is an abrupt temperature change, the radiator is plugged and needs to be flushed, cleaned or replaced. When troubleshooting a low heater output problem, use your infrared thermometer to check coolant flow through the heater core. Compare the temperature of the heater inlet and outlet hoses where they enter the firewall. Both should be hot, and the inlet hose should be about 20 degrees warmer than the outlet hose. If the outlet hose is not hot, the core is clogged or the heater control valve (if used) is defective. If
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reverse flushing the core fails to open the blockage, you will have to replace the heater core. Low heater output can also be caused by a thermostat stuck in the open position or the wrong temperature range thermostat. If the coolant temperature at the thermostat housing or radiator inlet is unusually low (140 degrees or less), the thermostat needs to be replaced.
MANY OTHER USES FOR INFRARED THERMOMETER An infrared thermometer can also help you diagnose poor A/C cooling performance. If the A/C system is fully charged and the compressor is operating, but the A/C is not blowing cold air there may be a blockage in the refrigeration circuit or a HVAC "blend air" door problem. A quick diagnosis can be made by first checking the temperature at the A/C outlet ducts with the system on maximum cool, recirculate air and highest blower setting. The A/C outlet temperature should be at least 25 degrees cooler than the ambient temperature. If not, visually inspect the liquid line to the evaporator for icing which would indicate an internal blockage. Next, visually inspect the condenser for obstructions and make sure the cooling fan is on. Then scan the surface of the condenser to check for abrupt temperature changes that would indicate an internal blockage. Parallel flow condensers should show an even drop in temperature from one side to the other. Serpentine condensers should show a drop in temperature from top to bottom. If blocked, the condenser should be reverse flushed or replaced. If no problems are found in the refrigeration circuit, the lack of cooling is in the HVAC unit or controls.
TROUBLESHOOTING DEAD CYLINDERS Some problems such as engine misfire can be time-consuming to troubleshoot. Isolating a misfire to a specific cylinder usually requires a power balance test (which is not easy to perform on some of today's distributorless ignition systems) or observing ignition patterns on an oscilloscope (which requires an expensive scope and making the necessary hookups). But now there is an easier way. Just use an infrared thermometer to measure and compare the temperature of the exhaust at each exhaust port. A misfiring cylinder does not produce as much heat energy as a good cylinder, so the exhaust from a weak cylinder will not be as hot as that from cylinders that are firing normally. To find the misfire, aim the gun at each exhaust port on the manifold and squeeze the trigger. Note each reading and compare the results. Any cylinders that are misfiring will read significantly lower than the others. Once you have identified the misfiring cylinder, you can zero in on the underlying cause. Remove and inspect the spark plug. If wet, the plug may be misfiring because of a bad plug wire, cracked distributor cap or bad coil on a DIS system. If the spark plug is fouled, the cylinder may have an oil consumption problem due to worn valve guides and/or rings. If the spark plug appears to be okay, the air/fuel mixture may be too lean. Check for a dirty or inoperative fuel injector, or an air leak around the injector seal. On older engines with carburetors, check for intake manifold air leaks. Another possibility may be a leaky valve. Check compression. This same procedure also works great on diesel engines. Reading and comparing exhaust temperatures can help to identify weak cylinders and diesel injector problems.
CATALYTIC CONVERTER TEMPERATURE CHECKS You can also use a noncontact thermometer to check the function of your catalytic converter. The converter may not be working if the catalyst has been poisoned by lead (leaded fuel), silicates (from an internal engine coolant leak) or phosphorus (oil burning), and your Check Engine light may be on with a P0420 Trouble Code. By measuring and comparing the converter inlet and outlet temperatures while the engine is idling, you can determine if the converter is doing anything or not. This type of quick temperature check won't tell you how efficiently the converter is working or whether or not it can pass an emissions test, but it will tell you if the converter is still functional. On older vehicles with two-way converters the difference should be at least 100 degrees F. But on 1981 and newer vehicles with three-way converters the difference may only be 20 to 30 degrees because computer-controlled engines normally run very clean. No difference in temperature indicates a defective converter or no air from the air pump (check the air pump diverter valve & plumbing). An increase of 500 degrees or more indicates converter overheating due to a rich fuel condition (check the fuel system) or misfiring spark plugs or compression leaks.
BRAKE TEMPERATURE CHECKS
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Troubleshoot Engine with Infrared Thermometer
You can use your infrared thermometer to diagnose certain brake problems, such as overheating and pulling. A difference side-to-side in front brake temperatures after stopping may indicate dragging or sticking calipers. Many race car teams use an infrared thermometer to check brake and tire temperatures to chck brake balance and tire loading.
Related Articles: Engine Overheating (causes) Cooling Fan (electric) Cooling Fan Relay Problems Air Conditioning (how to troubleshoot) Air Conditioning (not cooling) Catalytic Converters (troubleshooting a P0420 code)
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Troubleshoot Car Electrical Problem
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Troubleshoot Car Electrical Problem Copyright AA1Car
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Troubleshooting electrical problems can be a frustrating task, but it does not have to be if you keep a few simple rules in mind: Every circuit needs a power source; most electrical devices require a minimum voltage to function correctly; and all circuits require continuity. Consequently, most electrical problems are caused by low voltage (or no voltage), excessive resistance or a loss of continuity. SAFETY CONSIDERATIONS Safety is always an important consideration when working on automotive electrical systems. Except for the high voltage side of the ignition system, and the high voltage battery and circuits in hybrid vehicles, there is NO danger of being shocked. Twelve volts (12v DC) is not enough to be felt. The danger is accidentally shorting out a hot circuit and damaging the wiring, PCM or other onboard electronics, or starting a fire. CAUTION: If your vehicle is a hybrid with a high voltage battery, there is a risk of being shocked if you come into direct contact with the high voltage battery, wiring or other hybrid components. for more information on this subject, see Hybrid Safety Hazards CAUTION: When doing electrical repairs or replacing electrical or electronic component, the battery should ALWAYS be disconnected to eliminate any risk of causing an accidental short. Disconnecting the battery will cause most PCMs to forget their learned settings. This may cause driveability issues or require a special "relearn" procedure with a scan tool, so to avoid this kind of hassle use a 9 volt "memory saver" that plugs into the vehicle's power receptacle (cigarette lighter) to maintain voltage to the battery, or connect a 9 volt alkaline battery to the PCM power supply. For more information on safety, see Battery Safety . ELECTRICAL CIRCUIT CHECKS All electrical circuits require voltage to operate the components connected to that circuit. So if there is no voltage, there is no function. The first order of business when troubleshooting electrical problems, therefore, is to check for the presence of voltage at the load point in the circuit. The load point is the element that the circuit is supposed to power, such as a light bulb, wiper motor, blower motor, idle stop
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solenoid or whatever. And, all you need to quick check it is a voltmeter or a 12-volt test light that glows when there is voltage. A voltmeter is the best tool for this purpose because it will give you an exact reading, but a test light is OK for performing quick voltage checks.
Using a test light is a quick way to check for voltage, but a voltmeter is more accurate. Suppose you find no voltage at the load point. Ah ha, you have discovered your first clue about the problem. Check the fuse, fuse link or circuit breaker that protects the circuit, or the power relay that supplies voltage to the circuit. If the problem is a blown fuse, replacing the fuse may restore power temporarily, but unless the underlying cause for the overload is found and corrected, your "fix" probably will not last. Whatever you do, do not substitute a fuse of greater capacity. A larger fuse may be able to handle a greater load but the wiring and the rest of the circuit cannot. A circuit designed for a 20 amp fuse is designed to handle a maximum of 20 amps. Period. A faulty circuit breaker or an open relay will have the same effect as a blown fuse. Circuit breakers are often used to protect circuits that may experience brief periods of overloading such as an A/C compressor clutch. The easiest way to check a circuit breaker is to bypass it with a jumper wire. Your jumper wire should have a replaceable inline fuse to protect the circuit against damage. Use a fuse of no greater capacity than what the circuit itself uses. If you do not know, use a 5- or 10-amp fuse to be safe. If the circuit works when you bypass the circuit breaker, you have isolated the problem. Replace the circuit breaker. This same basic test can also be used to check a questionable relay. A relay is nothing more than a remote switch that uses an electromagnet to close a set of contact points. When the relay magnet is supplied with voltage, the points close and battery voltage is routed through the main circuit. Relays are often used in circuits to reduce the amount of wiring that is required, and to reduce the current that flows through the primary control switch. Thus, a relatively low amperage (make that cheap) switch, timer or sensor can be used to turn a much higher capacity relay on and off. VOLTAGE CHECKS FOR CAR ELECTRICAL PROBLEMS Every electrical device also requires a certain amount of voltage to operate. A light bulb will glow with reduced brilliance as the voltage drops. But for some components, there is a threshold voltage below which it will not operate at all. A starter motor may crank the engine more slowly with reduced voltage but, if the battery voltage is too low, it may not crank at all. Minimum threshold voltage is especially critical for such components as solenoids (which need a certain amount of voltage to overcome spring resistance), relays, timers, buzzers, horns, fuel injectors (which are solenoids, too) and most electronics (the ignition module, computer and radio). Checking the load point for full battery voltage will tell you whether or not sufficient voltage is getting through, and to do that you need a voltmeter. The battery itself should be at least 70 percent charged and read 12.43 volts or higher (12.66 volts is fully charged). If the battery is low, it should be recharged and tested. The output of the charging system should also be checked, and be about 1.5 to 2.0 volts higher than battery base voltage (around 14 to 14-1/2 volts). If the battery is OK, your voltmeter should read within 1 volt of battery voltage at the circuit load point in any given circuit. Low circuit voltage is usually caused by excessive resistance at some point in the wiring. Usually this means a loose or corroded connector, a faulty switch or relay or poor ground. To find the point of high resistance, use your voltmeter to do a "voltage drop test" at various points throughout the circuit. If the voltmeter shows a drop of more than a 0.4 volts across any connector, switch or ground contact, it means trouble. Ideally, the voltage drop should be no more than 0.1 volts. If low voltage is detected in a number of circuits, do a voltage drop test across the battery terminals and engine/body ground straps. Loose or corroded battery cables and ground straps are a common cause of voltage-related problems. Clean and tighten the battery cables and/or ground straps, as needed. Sometimes undersized wiring can cause low voltage. It is not something you will find in many original equipment wiring circuits, but it is a common mistake that is made in many do-it-yourself wiring installations for aftermarket accessories. The
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higher the amp load in the circuit, the larger the required gauge size for the wiring. The following list includes recommended wire gauge sizes: Wire size
Amp Capacity
18
6
16
8
14
15
12
20
10
30
8
40
6
50
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CONTINUITY Every electrical circuit requires a complete circuit to operate. Voltage to the load will not do any good unless there is also a complete ground path to the battery. The ground path in the case of all metal-bodied cars is the body itself. In plastic-bodied cars, a separate ground wire is needed to link the load to the chassis. In either case, a poor ground connection has the same effect as an open switch. The circuit is not complete so current does not flow. To check wiring continuity, you need an ohmmeter or a self-powered test light. An ohmmeter is the better choice because it displays the exact amount of resistance between any two test points. A test light, on the other hand, will glow when there is continuity but the intensity of the bulb may vary depending on the amount of resistance in the circuit. But it is OK for making quick checks. Never use an ohmmeter to check resistance in a live circuit. Make sure there is no voltage in the circuit by disconnecting it from its power source, by pulling the fuse or by testing downstream from the circuit switch or relay. Ohmmeters cannot handle normal battery voltage and, should you accidentally complete a circuit through the meter, you may damage your meter. Ohmmeters are great for measuring circuit resistance but you have to use care when checking electronic components. An ohmmeter works by applying a small voltage through its test leads, and this voltage can be enough to damage some electronic components (such as the oxygen sensor). Special high impedance 10,000 mega-ohmmeters should be used for electronics testing. Tracing wires is not as easy as it looks because the circuit wire will sometimes change color after passing through a connector, switch or relay. Always refer to a wiring diagram when possible. This way you will know how the wires are routed and what colors are used. FINDING ELECTRICAL FAULTS Now that we have covered some basic troubleshooting techniques, what is the best way to find an electrical fault fast? It depends on the nature of the problem. For a "dead" circuit, the first thing to look for is voltage at the load point. Use your voltmeter or 12-volt test light to check for voltage. If there is voltage, the problem is either a bad ground connection or the component itself has failed. Check the ground connection with your ohmmeter. If the ground connection is good, the fault is inside the component. If there is no voltage in the "hot" wire to the component, then the problem is in the wiring. Trace back through the fuse panel (or relay or circuit breaker) until you find voltage. Now look for an open or short that is preventing the current from reaching its correct destination. http://www.aa1car.com/library/tselec.htm
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Next comes bad connections. The resistance created by a loose or corroded connection will cause a voltage drop that can have an adverse effect on circuit components. An ohmmeter can be used to check non-powered circuit connections for excess resistance, but a better method is to use a voltmeter to check for a voltage drop across a connection.
The voltmeter leads are connected on either side of the circuit component or connection that is being tested. If a connection is loose or corroded, it will create resistance and produce a reading on the voltmeter. As stated earlier, a voltage drop of more than 0.4 volts means trouble, and ideally it should be 0.1 volts or less. For more information about voltage drop testing, Click Here The worst kind of electrical problem to troubleshoot is an intermittent one. Everything works fine in the shop but as soon as the customer gets the car back it starts to act up again. An intermittent open or short is usually the result of something heating up and breaking (or making) contact, or something that is loose and is making periodic contact. Loose or corroded connections and switches are often responsible for this kind of problem, so try jiggling the wires and circuit switch to see if it changes circuit voltage or resistance. A wire that is rubbing and has chaffed away some of its insulation can make intermittent contact causing a short, so again wiggling suspicious wires will often reveal the problem. Temperature-sensitive intermittent shorts or opens can be the hard to identify because you frequently have to simulate the exact circumstances that cause them to happen. Sometimes you can assume what is happening by the nature of the problem. But it is always more satisfying (and assuring) to duplicate the problem so you know for sure what is wrong. When does the problem occur? Does it only happen when the engine is hot or after the circuit has been on for a period of time? Using a hot air gun or hair dryer to heat wires, connectors, switches and relays can sometimes help identify troublesome components. Environmental factors often play havoc with electrical systems, too. Road splash or water leaking through a crack in the cowl, under the windshield or around a grommet can sometimes short out a circuit. Look for obvious signs of corrosion or leakage, and if you find none check the condition of nearby weather seals. A final note on repairing electrical faults: When splicing wires do not just twist them together and wrap electrical tape around the connection. Use a solderless crimp-on connector, or twist the wires together, solder them and use shrink wrap electrical insulation tubing to seal the repair.
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Engine Vacuum Leaks
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Engine Vacuum Leaks
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Copyright AA1Car Have you ever tried to tune an engine only to find it won't idle or run right? Or have you ever been confronted with an engine that just doesn't seem to run right no matter what you've done or replaced? You may be dealing with an engine vacuum leak. Sometimes a vacuum leak will whistle or hiss and make itself obvious. But oftentimes, a vacuum leak will disguise itself as an ignition or fuel problem that defies diagnosis. Either way, an engine vacuum leak is bad news because allows "unmetered" air to enter the engine and upset the air/fuel ratio. So how do you know when a vacuum leak is causing a problem? If the engine is experiencing any of the following symptoms, a vacuum leak is probably responsible: Too fast an idle speed. If an engine without computerized idle speed control is idling too fast and refuses to come down to a normal idle speed despite your best efforts to back off the carburetor idle speed screw or air bypass adjustment screw (fuel injection), air is getting past the throttle somewhere. Common leak paths include the carburetor and throttle body gaskets, carburetor insulator spacers, intake manifold gaskets, and of course, any of the engine's vacuum fittings, hoses and accessories. It is even possible that leaky O-rings around the fuel injectors are allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft. A rough idle or stalling. A performance cam with lots of valve overlap can give an engine a lopping idle, but so can a vacuum leak. A really serious leak can lean the air/fuel mixture out to such an extent that an engine won't idle at all. An EGR valve that is stuck open at idle can have the same effect as a vacuum leak. So too can the wrong PCV valve (one that flows too much air for the application), or a loose PCV hose. The rough idle in these cases is caused by "lean misfire." The fuel mixture is too lean to ignite reliably so it often misfires and fails to ignite at all. Lean misfire will show up as elevated hydrocarbon (HC) readings in the exhaust, enough, in fact, to cause a vehicle to fail an emissions test. Hesitation or misfiring when accelerating. This may be due to a vacuum leak, but it can also be caused by a weak or inoperative accelerator pump in a carburetor, dirty injectors, or even ignition problems such as a cracked coil,
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worn spark plugs or incorrectly gapped plugs. An idle mixture that defies adjustment. When setting the idle mixture adjustment screws on a carburetor, the idle speed should start to falter as the adjustment screws are turned in to lean out the mixture. If the screws seem to have little or no effect on idle, you have either got a carburetor problem or a vacuum leak. The important thing to keep in mind about vacuum leaks is that they have the most noticeable effect at idle. At part and full throttle, there is so much air entering the engine that a little extra air from a vacuum leak has a negligible effect. TIP: If you have a scan tool, look at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values. Normal range is plus or minus 8. If the numbers are +10 or higher for STFT and LTFT, the engine is running LEAN. If you rev the engine to 1500 to 2000 rpm and hold it for a minute or so, and the STFT value drops back down to a more normal reading, it confirms the engine has a vacuum leak at idle. If the STFT value does not change much, the lean fuel condition is more likely a fuel delivery problem (weak fuel pump, restricted fuel filter, dirty fuel injectors or a leaky fuel pressure regulator) than a vacuum leak.
For more information about using fuel trim to diagnose a lean fuel condition, see What Is Fuel Trim?, or view this article on Fuel Trim by Wells Manufacturing (PDF file). Before we get into the various techniques of finding and fixing vacuum leaks, let's quickly review vacuum's role in fuel delivery.
WHAT IS INTAKE VACUUM?
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Intake vacuum exists in the intake manifold as a result of the pumping action of the engine's pistons and the restriction created by the throttle valve. Were it not for the throttle choking off the flow of air into the engine, there would be little if any vacuum in the intake manifold (like a diesel). The downside of intake vacuum is that it creates pumping losses and reduces engine efficiency. On older carbureted engines, vacuum is needed to pull fuel into the engine. Vacuum siphons fuel through the idle, main metering and power circuits. An engine with a vacuum leak, therefore, will likely be an engine that suffers from the symptoms of lean carburetion such as lean misfire, hesitation, stalling and rough idle. But the same symptoms can also be caused by a clogged catalytic converter or other exhaust restriction, a leaky EGR valve or valve timing problems (all of which reduce intake vacuum).
Engines with Multiport Fuel Injection and Gasoline Direct Injection don't need vacuum to pull fuel into the engine because it is sprayed in under pressure. Even so, most of these engines still have a throttle for regulating airflow and engine speed. And like the older carbureted engines, a throttle body also creates an airflow restriction that creates vacuum inside the intake manifold. On most engines, intake vacuum should be steady between 16 and 22 inches Hg (Mercury). A lower reading usually indicates a vacuum leak, or one of the other problems just mentioned. A reading that gradually drops while the engine is idling almost always points to an exhaust restriction. An oscillating vacuum reading usually indicates a leaky valve or badly worn valve guides that leak vacuum. Although fuel injected engines do not rely on intake vacuum to pull fuelinto the engine, vacuum leaks can upset the carefully balanced air/fuel ratio by allowing "unmetered" air to enter the engine. The result is the same kind of driveability symptoms as a vacuum leak on a carbureted engine (lean misfire, hesitation when accelerating, rough idle and possibly even stalling). Common leak points include injector O-rings, intake manifold gaskets, idle air control circuit and the throttle shaft. Fuel injected engines also rely on intake vacuum to regulate the fuel pressure behind the injectors. Fuel delivery cannot be accurately metered unless a fairly constant pressure differential is maintained. So the fuel pressure regulator diaphragm is connected to a source of intake vacuum. Vacuum working against a spring-loaded diaphragm inside the regulator opens a bypass that shunts fuel back to the tank through a return line. This causes the fuel pressure in the injector rail to rise when http://www.aa1car.com/library/vacleak.htm
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Engine Vacuum Leaks
engine load increases (and vacuum drops). Thus, the regulator uses vacuum to maintain fuel pressure and the correct air/fuel ratio. A vacuum leak changes the equation by causing a drop in vacuum and a corresponding increase in line pressure.
MEASURING INTAKE VACUUM Vacuum is measured with a vacuum gauge. Most are calibrated in inches Hg (Mercury), but you may also see some gauges that are also calibrated in inches of H20 (water) or kilopascals (kPa) or even bars. One inch of vacuum measured in inches Hg equals 13.570 inches in H20, 0.4898 psi (pounds per square inch) or 3.377 kPa. Here's a conversion table you can use to convert units of measurement: From:
To:
kilopascal [kPa] newton/square meter newton/square centimeter newton/square millimeter bar millibar [mbar] microbar [µbar] psi [psi] inch mercury (60°F) [inHg] inch water (60°F) [inAq]
kilopascal [kPa] newton/square meter newton/square centimeter newton/square millimeter bar millibar [mbar] microbar [µbar] psi [psi] inch mercury (60°F) [inHg] inch water (60°F) [inAq]
Result:
pressure conversion factors provided by unitconversion.org
ENGINE VACUUM LEAK DETECTION Okay, now that we have covered what a vacuum leaks do, how do you find components that leak vacuum? One way is to visually inspect all the vacuum hoses and connections. Look for disconnected, loose or cracked hoses, broken fittings, etc. Hey, you might get lucky and find the problem in a few minutes, or you might waste half the day trying to find the mysterious leak. Vacuum leaks are often the elusive needle in a haystack. And if it is not a hose leaking vacuum but something else such as a gasket, worn throttle shaft, injector O-rings, etc., you may never find it using this technique. A faster technique for finding intake manifold vacuum leaks is to get a bottle of propane and attach a length of rubber hose to the gas valve. Open the valve so you have a steady flow of gas. Then hold the hose near suspected leak points while the engine is idling. If there is a leak, propane will be siphoned in through the leak. The resulting "correction" in the engine's air/fuel ratio should cause a noticeable change in idle speed and/or smoothness (Note: on engines with computerized idle speed control, disconnect the idle speed control motor first). Aerosol carburetor cleaner can also be used the same way. CAUTION: Solvent is extremely flammable, so do not smoke or use it if there are any sparks in the vicinity (arcing plug wires, for example). Spray the solvent on suspected leak points while the engine is idling. If there is a leak, the solvent will be drawn into the engine and have the same effect as the propane. The idle speed will suddenly change and smooth out. TIP: If you have a scan tool, look at the Short Term Fuel Trim (STFT) value while you are using carb cleaner or propane to check suspected vacuum leak points. If there is a leak and some of the cleaner or propane is sucked in through the leak, you will see a momentary drop in the STFT reading. This confirms you have found a leak (keep checking because there may be multiple leaks!).
USING A SMOKE MACHINE TO FIND ENGINE VACUUM LEAKS A much safer technique is to use a smoke machine. These machines feed artificial smoke into the intake manifold, The smoke may also be mixed with an ultraviolet dye to make leaks easier to see. You then look for smoke seeping out of hoses, gaskets or cracks in the manifold and/or use a UV light to find the leak. This type of equipment is often needed to find small air leaks in the EVAP (evaporative emissions) control system. Smoke machines can cost $600 to $2000 or more http://www.aa1car.com/library/vacleak.htm
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depending on the model and features, so they are primarily for use by professional technicians.
FINDING LEAKS WITH AN EXHAUST ANALYZER Propane can also be used in conjunction with an exhaust analyzer (do NOT use carburetor cleaner or you may damage your analyzer!). Engine vacuum leaks almost always cause fluctuating HC readings, so an infrared exhaust analyzer can (1) tell you if there is indeed a leak, and (2) where the leak is using the propane procedure. Two types of vacuum leaks can be diagnosed with an analyzer. The first kind is a general vacuum leak (PCV hose, brake booster, etc.) that leans out the mixture and causes a very low CO reading and only a slightly higher fluctuating HC reading. The O2 reading will also be high. The second kind of vacuum leak is a "point" leak that affects only one or two cylinders (a leaky manifold gasket or a crack or porosity leak in one of the manifold runners). This will be indicated by a normal or low CO reading combined with high fluctuating HC readings. O2 will again be high. To find a leak, feed propane at suspected leak points until you note an improvement in idle quality and/or a change in the HC/CO/O2 readings. When you have found the leak, the idle should smooth out, HC and O2 should drop and CO rise. It is important to note that an overly lean idle mixture will also cause a fluctuating HC reading the same as a vacuum leak. To tell one from the other, there is a simple "trick" you can use. Momentarily enrich the idle mixture to 1.5 to 2.0% CO by placing a clean shop rag over the top of the carburetor. If the engine smooths out and HC drops and remains stable, the problem is a lean idle mixture adjustment. If HC still fluctuates, however, the engine is still too lean in one or more cylinders indicating a vacuum leak.
ELECTRONIC VACUUM LEAK DETECTION If you like gadgets, there are electronic tools designed to detect vacuum leaks. An electronic vacuum leak detector will beep or flash when it detects ultrasonic vibrations that are characteristic of a vacuum leak. These tools use a sensitive microphone to listen for certain noise frequencies. Though extremely sensitive, these tools sometimes react to tiny leaks that are not really causing a problem, or "false" leaks such as the noise created by arcing inside the distributor cap or normal bearing noise in the alternator.
PRESSURE VACUUM LEAK DETECTION TECHNIQUES Another way to find an elusive vacuum leak is to pressurize the intake manifold with about three lbs. of regulated air. This can be done by attaching a regulator to your shop air hose, then attaching the hose to a vacuum fitting or the PCV valve fitting on the intake manifold, carburetor or throttle body. Do not apply too much pressure or you may create new leaks! With the engine off and air flowing into the manifold, spray soapy water on suspected leaks. If you see bubbles, you have found the leak. You can also use the opposite technique, which is to apply vacuum with a hand-pump to various vacuum hoses and circuits to see if they hold vacuum. But this technique means tracing the entire circuit to see where it ends, and disconnecting and plugging any parts of the circuit that do not "dead end" against a diaphragm or valve.
HOW TO REPAIR AN ENGINE VACUUM LEAK Okay, now you have found the leak. Here are some suggestions on how to fix it: * Leaky vacuum hoses Replace them. If the end of a hose is loose or cracked, cutting it off and sticking it back on may temporarily eliminate the leak. But if the hose is rotten or age hardened, it needs to be replaced. Shortening hoses may also create additional problems. The hose may chaff or rub against other components, or pull loose as a result of engine motion and vibration. Use the correct type of replacement hose (PVC hose or vacuum hose capable of withstanding fuel vapors and vacuum without collapsing). Also, be sure the replacement hose is the same diameter and length as the original.
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* Carburetor or throttle body base gasket vacuum leaks Try tightening down the carburetor or throttle body mounting bolts. If that doesn't stop the leak, replace the gasket under the carburetor or throttle body. If there is a heat insulator or adapter plate under the unit, it may also have to be replaced depending on its condition. While the carburetor or throttle body is off, use a straightedge to check the base for flatness (and the manifold, too). Warped surfaces can prevent a tight seal, so if you find any it calls for resurfacing or component replacement.
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* Carburetor or throttle body throttle shaft vacuum leaks Wear here can only be repaired by resleeving the throttle shaft, which for all practical purposes means replacing the carburetor or throttle body with a new or remanufactured unit.
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* Intake manifold gasket vacuum leaks Try retorquing the intake manifold bolts, working from the center out in the recommended tightening sequence. If that fails, the intake manifold will have to be removed and the intake gaskets replaced. Sometimes the mating surface of the intake manifold or the heads will not be flat (check both with a straightedge). If warped, the intake manifold and/or heads will have to be resurfaced on a milling machine. Another problem to watch out for here are heads that have been milled or resurfaced to raise compression. To maintain proper alignment between the manifold and heads, metal also needs to be machined off the bottom of the manifold where it mates with the block, otherwise it will sit to high and the ports and bolt holes won't align. * EGR valve leaks If the valve isn't closing all the way due to carbon deposits on the stem or valve seat, cleaning may be all that is needed to cure the problem. Otherwise, the engine will need a new EGR valve. * Leaky power brake booster Replace it. But first make sure it is the booster and not just the hose or check valve that is leaking.
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Related Articles: What Is Fuel Trim? Troubleshooting Idle Speed Control System Carburetors Troubleshooting Hesitation Problems Positive Crankcase Ventilation Exhaust Gas Recirculation
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Engine Tune-up
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Engine Tune-Up Copyright AA1Car
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. The word Tune-up is an oputdated and obsolete term. The need for tune-ups went out back in the mid 1980s when fuel injection replaced carburetors and conventional spark plugs were replaced with long life platinum spark plugs. Yet many people think their engine still needs a tune-up. What is needed is preventive maintenance. Or, if your Check Engine Light is on, what you need is a diagnostic scan to determine what is causing the fault. If your engine is hard to start, stalls, runs rough, gets poor fuel mileage, doesn't run right, or is experiencing any other kind of driveability or emissions problem, you don't need a tune-up. You need a diagnostic check to find out what's causing the problem. The only engines that still need a tune-up today are old ones from the early 1980s and back that have carburetors and distributors. Yet the tune-up myth persists, and may people still think it is some kind of "cure-all" for what ails their engine. To make matters worse, many new car dealers tell their customers they need a 60,000 mile "major" tune-up (whatever that is).
Tune-Up Definition is Undefined There's no common definition of what exactly a tune-up should include, but most would agree that it involves replacing the spark plugs and performing other adjustments to the idle speed, fuel mixture and spark timing that are necessary to maintain or restore like-new engine performance. The problem is there is almost nothing that can adjusted or "tuned" under the hood on late model engines with computerized engine controls. Ignition timing is fixed and controlled by the engine computer, as is idle speed and the fuel mixture. Base timing can be checked with a scan tool, but cannot be adjusted on most engines. The same goes for idle speed and various emission functions. A scan tool can reveal if the systems are functioning normally, but in most cases no adjustments are possible because the adjustments are programmed into the computer. A simple maintenance type tune-up (a new set of plugs) may make an engine easier to start, improve fuel economy, lower emissions, restore lost pep and power if the old spark plugs are worn or fouled. But if the problem is due to something else, a new set of plugs alone won't help. A tune-up under these circumstances is a waste of time and money. The engine needs to be diagnosed to find out what is wrong.
TUNE-UP CHECKS http://www.aa1car.com/library/tuneup1.htm
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An engine check-up should start with a scan for any current, pending or past fault codes. This requires plugging a scan tool or code reader into the vehicle diagnostic connector so the tool can communicate with the powertrain control module (PCM). The onboard diagnostic system does an excellent job of monitoring all the key systems, and on most 1996 and newer vehicles it can even detect engine misfires. If no faults are found, and the engine is running normally, the check-up is not over because there are additional things that should also be checked (especially if the engine is NOT running normally or any fault codes were found with a scan tool): Battery voltage Charging voltage Power balance or dynamic compression (to identify any mechanical problems such as leaky exhaust valves, worn rings, bad head gasket, bad cam, etc. that could adversely affect compression and engine performance) Engine vacuum (to detect air leaks as well as exhaust restrictions) Operation of the fuel feedback control loop (to confirm that the system goes into closed loop operation when the engine warms up) Check exhaust emissions (this should be a must in any area that has an emissions testing program to confirm the vehicle's ability to meet the applicable clean air standards, and to detect gross fuel, ignition or emission problems that require attention) Verify idle speed (should be checked even if computer controlled to detect possible ISC motor problems); Idle mixture (older carbureted engines only, but injector dwell can be checked on newer vehicles to confirm proper feedback fuel control) Check ignition timing -- if possible (should be checked even if it is not adjustable to detect possible computer or sensor problems) Operation of the EGR valve. OTHER CHECKS In addition to these performance checks, hoses and belts should be visually inspected. All fluids (oil, coolant, automatic transmission fluid, power steering fluid and brake fluid) should also be inspected to make sure all are at the proper level, and that the appearance and condition of each is acceptable. There should be no sludge in the oil, the ATF should not smell like burnt toast, the coolant should have the proper concentration of antifreeze and not be full of rust or sediment, the brake fluid should be clear and not full of muck, etc. WHAT TO REPLACE If the tune-up checks find no major faults, the following items can be replaced for preventive maintenance: Spark plugs (gapped to the correct specs, of course). Consider long life platinum or iridium spark plugs on applications where plug accessibility is difficult or where longer service life may be beneficial Rotor and/or distributor cap (if required) Fuel filter; Air filter; PCV valve and breather filter Other parts on an "as needed" basis (things like spark plug wires, belts, hoses, fluids, etc.) Check and adjust (if required on older vehicles) ignition timing, idle speed and idle mixture; O2 sensor(s). OXYGEN SENSORS Oxygen sensors on late model vehicles should last 100,000 to 150,000 miles under normal driving and operating conditions (which does NOT include an engine that burns oil, or vehicles that have been under water!). The oxygen sensor is a key sensor that can hurt fuel economy if it is getting old or has failed. One EPA study found that up to 70% of high mileage vehicles that fail an emissions test need a new O2 sensor. So does that mean the oxygen sensors should be replaced as part of a tune-up? Not unless they are defective or are acting very sluggish. Oxygen sensor performance can be verified with a scan tool, and a bad oxygen sensor will usually set a fault code and turn on the Check Engine Light, but not always. If an oxygen sensor fails or is getting sluggish, it will usually cause the engine to run rich. This causes an increase in fuel consumption and emissions. It usually does not hurt performance or cause other driveability issues. Oxygen sensors are expensive to replace. They typically cost $35 to $70 each, and some may cost upwards of $200 or more depending on the application. In addition, V6 and V8 engines have one oxygen sensor for each cylinder bank, and some have two. There are also one or more oxygen sensors in the exhaust system to monitor the catalytic converter(s). So oxygen sensors are not something you want to replace unless it is absolutely necessary. Some manufacturers do recommend replacing oxygen sensors for preventive maintenance, however. The recommended http://www.aa1car.com/library/tuneup1.htm
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replacement interval for unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s applications is 30,000 to 50,000 miles. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications should be changed every 60,000 miles. And on OBD II equipped vehicles (all 1996 and newer), some recommended replacing the oxygen sensors at 100,000 mile intervals. CLEANING FUEL INJECTORS
AccuSparkâ&#x201E;˘ Ignition AccuSparkâ&#x201E;˘ Electronic Ignition kits 10% Sale Discount CODE: AC10 Dirty fuel injectors are a common problem that can hurt engine performance, fuel economy and emissions. Many experts recommend cleaning the fuel injectors and intake system as part of a tune-up. The need for injector cleaning isn't as great as it once was thanks to improved fuel additives and redesigned injectors. But in areas that have gone to reformulated gasoline, injector clogging is more of an issue. Fuel varnish deposits that form in injectors restrict fuel delivery, which has a leaning effect on the air/fuel mixture. The result can be lean misfire and a general deterioration in engine performance and responsiveness. Deposits can also build up on the backs of intake valves, causing cold hesitation problems in many engines. The cure is to clean the injectors and valves. Cleaning is recommended for any engine that is suffering a performance complaint or has more than 50,000 miles on the odometer. Cleaning the throttle body can also help eliminate idle and stalling problems that plague many of today's engines.
THE 100,000 MILE "NO TUNE-UP" MYTH The spark plug replacedment interval on most late model engines with platinum or iridium spark plugs is 100,000 miles. But that does not mean the engine requires no maintenance whatsoever for 100,000 miles. Regular oil and filter changes are still necessary to maintain proper engine lubrication. Most experts still recommend changing the oil and filter 3,000 miles or three to six months. The oil change interval can be stretched out to reduce maintenance costs if a vehicle is driven under ideal conditions (no extremely hot or cold weather, no short trip, stop-and-go driving, no excessive idling, no extremely dusty road conditions, no trailer towing, no turbocharging). But the average driver is more often than not a "severe service" driver so should follow the 3,000 mile change interval. Today's 100,000 mile tune-up interval also skirts around the issue of fuel filter and air filter replacement. A number of new cars and trucks now have "lifetime" fuel filters, most of which are located inside the fuel tank with the electric fuel pump.
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Such a filter might go 100,000 miles. Then again, it might not. A couple of tanks of bad gas or some corrosion caused by accumulated moisture can cut short the life of any filter, even a so-called lifetime filter. Sooner or later even a lifetime fuel filter will have to be replaced. As for air filters, the service life depends more on environmental factors rather than time or mileage. If a vehicle is driven on gravel roads, filter life may only be a few months or few thousand miles. Many vehicles also have a cabin air filter for the passenger compartment. This also needs to be replaced at specific intervals (see your owners manual for the location and recommended service interval). Repairs are also inevitable regardless of what the tune-up interval is supposed to be. It's pretty unlikely that a set of front disc brake pads will go 100,000 miles in city driving -- 20,000 to 30,000 miles is a more realistic figure. The same goes for belts, hoses, the battery, water pump, exhaust system and many other parts. No vehicle that's yet been built can even come close to going 100,000 miles without needing some type of maintenance or repair.
THE 60,000 MILE MAJOR TUNE-UP RIP-OFF Some car dealers continue to promote a 60,000 mile major tune-up that includes a long list of items they supposedly check, and may also include normal tune-up replacement parts such as spark plugs and filters. They may also do a coolant flush, transmission flush and/or brake fluid flush. The service is fairly expensive ($250 to $1000 or more!), and is probably unnecessary provided you have changed your oil regularly, you have kept your fluid levels full, and the engine is not experiencing any problems. I think people who spend this kind of money to have their engine examined should also have their head examined. But if you want to pay for a "piece-of-mind" check-up, your new car dealer will be more than happy to accommodate you.
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About Spark Plugs
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About Spark Plugs Copyright AA1Car The spark plugs are the business end of the ignition system. The spark plugs deliver the spark needed to ignite the air/fuel mixture. No spark means no combustion, wasted energy, increased emissions, loss of performance, idle roughness, hesitation, hard starting and possibly even a no start if all of the plugs are affected. Consider for a moment what happens when a spark plug fires. The spark is created when high voltage supplied by the ignition coil jumps across a small air gap between the plug electrodes. The high voltage surge from the coil goes down the plug center electrode, ionizes the air between the electrodes (the air gap) and forms a spark (arc) as it jumps across the gap to the outer ground electrode. The initial voltage required to form the spark may range from 4,000 up to 28,000 volts depending on the distance between the electrodes, engine load and compression (larger distances, higher engine loads and compression all raise the firing voltage requirements). The spark only lasts about a millisecond, but it is long enough to start the burn.
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.. The instant at which the spark occurs is timed precisely to coincide with the position of the piston as it approaches top dead center on its compression stroke. On most engines, the spark occurs a few degrees before the piston reaches top dead center. If the spark occurs too soon (over advanced timing), cylinder pressures rise too quickly and peak too early in the cycle resulting in a loss of power. This can also cause engine damaging "detonation" (spark knock or ping) to occur. If the
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spark occurs too late, cylinder pressures peak too late in the cycle also resulting in a loss of power. Timing is controlled by the engine computer and ignition module, not the spark plugs, so a timing problem would indicate a sensor or module problem. SPARK PLUG PROBLEMS If an engine cranks but will not start, one of the first things you should check is spark. No spark at any of the plugs usually indicates an ignition problem that requires further investigation (a bad coil, ignition module, distributor pickup, crank sensor, etc.). If the engine runs but misfires, one or more spark plugs may be worn or fouled, or there may be one or more bad spark plug wires. To diagnose this kind of problem, observe the firing pattern for each cylinder on an oscilloscope. A higher than normal firing voltage in any one cylinder may indicate excessive resistance in a plug wire, a loose plug wire, or a badly worn or misgapped spark plug (too wide). A lower than normal firing voltage in any one cylinder may indicate a shorted plug wire, or a fouled or damaged spark plug. Spark Plug Fouling is the number one reason why spark plugs have to be replaced. Plugs also have to be replaced for preventive maintenance because the electrodes wear as the plugs age. This increases the distance between the electrodes which in turn leads to a gradual increase in the firing voltage required to jump the gap. The gap on a standard spark plug grows about 0.00063 to 0.000126 inch for every 1,000 miles of normal driving, which means the firing voltage requirements creep up about 500 volts for every 10,000 to 15,000 miles of driving. Eventually the plugs firing voltage requirements under load exceed the ignition system output resulting in a misfire. But most plugs foul out long before they are worn out. A single fouled spark plug is bad news because it can kill up to 25% of a four cylinder engines power output. It is like riding a horse with a broken leg. A fouled plug will also cause a big increase in fuel consumption and emissions (more than enough to cause an emissions failure and/or the check engine light to come on if the vehicle has an OBD-II system). Fouling can occur if fuel or oil deposits build upon the plug electrodes. The ceramic insulator around the center electrode prevents voltage from finding a shortcut to the steel plug shell and ground. Deposits here may form a conductive path for the voltage to bleed off to ground, preventing it from jumping the gap and making a spark. Deposits around the outer ground electrode or between the electrodes may form a barrier or bridge that also prevents a spark from occurring. Fouling can be a problem if an engine uses oil. Worn valve guide seals and guides can allow oil to be sucked down the guides and into the combustion chamber. A heavy buildup of thick black deposits on the plug and intake valve would indicate such a problem. Worn or broken rings, or damage to the cylinder wall can also allow oil to enter the combustion chamber and form ash deposits on the plugs. Extensive idling and/or short trip stop and go driving can also lead to a rapid buildup of normal fuel deposits. This occurs because the plugs never get hot enough to burn off the deposits, something which plugs are designed to do. Powdery black deposits on the plugs can occur from "carbon fouling." The underlying cause here is a rich fuel mixture. On an older carbureted engine, the problem might be a broken or stuck choke. On a fuel injected engine, the problem might be a leaky injector, or a dead oxygen sensor or coolant sensor that prevents the engine control system from going into closed loop and leaning out the fuel mixture. Reading Spark Plugs
Click on image at left to view Spark Plug Diagnosis Chart.
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Reading the condition of the old spark plugs can reveal a lot about what may have caused a plug to foul out as well as other problems that may be going on inside the engine, things like lean fuel mixture, rich fuel mixture, oil burning, overheating, overadvanced ignition timing, detonation/preignition and more. Replacing the spark plugs will not solve any of these problems, and the new spark plugs will likely suffer the same kind of fouling, wear or damage unless the underlying problem is diagnosed and repaired. SPARK PLUG HEAT RANGE
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About Spark Plugs
The "heat range" of a spark plug determines how hot the plug runs during normal operation. If the heat range is correctly matched to the engine application, the plug will run hot enough under normal driving conditions to burn off fouling deposits before they can cause problems. Likewise, the plug will not get too hot and become a source of ignition causing enginedamaging preignition and detonation. If the heat range is too cool for the application, though, fouling deposits may build up faster than they are burned off. For this reason, always follow the vehicle manufacturer or plug supplier heat range recommendations when selecting a spark plug for a particular application. Two spark plugs may appear to be identical on the outside but have entirely different heat ranges. There are situations, though, that may require a slightly hotter or colder plug than the one normally recommended. Switching to a slightly hotter plug can help reduce fouling in an older engine that uses oil, for an engine that spends a lot of time idling or is used for short trip stop-and-go driving. But a hotter plug should not be used unless an engine is experiencing a fouling problem because of the increased risk of preignition and detonation. For performance applications (racing, or engines that are run under heavier than normal loads or at high rpm for sustained periods of time), switching to a slightly colder plug can minimize the risk of preignition and detonation. Even so, a colder plug can increase the risk of fouling with extended idling and low speed operation. Many of today's spark plugs have a very broad heat range because the plug manufacturer uses a copper core or platinum center electrode. Copper is an excellent conductor of heat, so the insulator can be designed to run hotter and burn off fouling deposits without it getting too hot under increased load to cause preignition or detonation. A solid platinum center electrode will also carry heat away from the tip, but not if the electrode only has a platinum tip. SPARK PLUG REPLACEMENT OPTIONS
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The recommended replacement interval for standard spark plugs has typically been every 30,000 to 45,000 miles. But most of extended life plugs have special wear-resistant electrodes made of platinum, iridium, nickel yttrium or other exotic alloys that minimize electrode erosion. Such plugs can usually go 100,000 miles plus with little or no electrode wear. Even so, they may still be vulnerable to fouling if an engine has an oil consumption problem or spends excessive amounts of time idling. Extended life spark plugs are a good upgrade for many engines, but may not be the best choice for an older engine that uses oil or even some performance engines. According to one plug manufacturer, platinum tipped electrodes run hotter than standard electrodes. This may increase the risk of preignition and detonation in some turbocharged and high performance engines. For such applications, a standard plug with a colder heat
range might be a safer choice. There are also a wide variety of electrode configurations from which to choose today. Each manufacturer claims certain performance benefits for their particular design. It may be reduced electrode wear, or improved ignition reliability, or both. Such plugs are often marketed as "premium" or "performance" plugs, and may command a price of up to $6 or $7 apiece. Some of these plugs (as well as standard plugs) also have multiple electrodes (two, three or four ground electrodes). A spark plugs with more than one ground electrode will still only produce one spark per ignition cycle. But with four paths from which to choose, the likelihood of getting a good spark to at least one of the ground electrodes is multiplied for improved ignition reliability. Having more than one ground electrode also distributes the wear to minimize electrode erosion and growth of the spark gap over time. Some such plugs also experience a self-cleaning effect because the sideways path of the spark helps burn deposits off of the insulator. Are premium plugs worth the extra money? They are if they can provide extended plug life, reduce the need for maintenance or improve overall ignition performance. The plugs in many front-wheel drive cars and minivans with V6 engines are very difficult to replace. Installing extended life plugs can almost eliminate the plug change hassle for good. Likewise, performance plugs that reduce misfires can enhance performance for a smoother running, cleaner more fuel efficient engine. No spark plug can create power out of thin air, but improved ignition reliability can minimize any horsepower loss due to misfire. CHANGING SPARK PLUGS
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About Spark Plugs
When changing spark plugs, wait until the engine has cooled to remove the plugs. The engine should be at or near room temperature, and not hot to the touch. This is very important with aluminum cylinder heads because it reduces the risk of damaging the threads in the cylinder heads when the plugs come out (aluminum is a much softer metal than cast iron). Most threads on spark plugs for engines with aluminum heads are either precoated to reduce the risk of thread damage, or the plug shell is made of a nickel alloy. If the plug shell is black or plain steel, however, you should put some antiseize to the threads, and reduce the applied torque by about 30 to 40%. Do not use antiseize if the plug shell is nickel or has been precoated. Antiseize acts like a lubricant and may allow too much torque to be applied to the plugs, damaging the treads in the cylinder head.
Watch Out for Ford Motorcraft Two-piece Spark Plugs That Break! The original equipment Motorcraft brand spark plugs that were factory installed in many late model (2004 to 2008) Ford trucks with 5.4L V8 and 6.8L V10 engines, 2005 to 2007 Mustang GT 4.6 & 5.4L V8 engines, and 2008 Mustang GT models built prior to 11/30/07) can break when you attempt to remove them! The spark plugs have a crimped lower electrode shell that becomes coated with carbon, causing it to stick in the cylinder head. When you attempt to unscrew the plug, the lower shell breaks off and stays in the head. Removing the broken shell requires a special Ford, Snap-On or Lisle extractor tool. Worse yet, if any shell or electrode fragments fall into the cylinder and can't be fished out, you may have to remove the cylinder head to get the debris out. Many experts recommend replacing the original equipment Motorcraft spark plugs before the get too many miles on them (over 35,000). Replacing the plugs at low mileage will reduce the risk of them sticking and breaking. Waiting until the original equipment spark plugs have 100,000 miles on them is asking for trouble! Ford Technical Service Bulletin 08-7-6 covers the recommended removal procedure for these spark plugs, as well as the repair procedure if one or more plugs break ( Click Here to View Ford TSB 08-7-6). Essentially, it says to remove the spark plugs when the engine is COLD (room temperature). Loosen the plugs about 1/8 to 1/4 turn, stop and spray some WD-40 or penetrating oil into the spark plug well. Allow the oil to soak into the threads so it can loosen the carbon around the electrode shell. Wait at least 15 minutes, or longer (overnight is recommended if the plugs have over 80,000 miles on them). Then slowly loosen the plugs, applying no more than 35 ft. lbs of torque to your wrench. If a plug sticks, retighten it half a turn, apply more penetrating oil, wait, then try again. Do NOT reinstall the same Motorcraft spark plugs (PZT 2FE Platinum). Replace them with a much improved one-piece spark plug from Champion (7989), or a similar spark plug from NGK, Denso or Bosch. Apply nickel anti-seize to the outer surface of the lower electrode shell (the smooth part) before installing the plugs. For more information about the Ford spark plug breakage problem Click Here. TIGHTENING SPARK PLUGS: BE CAREFUL! How much the spark plugs should be tightened depends on the size of the plugs and the type of plug seat. Spark plugs with gasket style seats require more torque than those with taper seats. Always follow the vehicle manufacturer torque recommendations, but as a general rule 14 mm plugs with a gasket style seat should be tightened to 26 to 30 ft.lbs. in cast iron heads, but only 18 to 22 ft.lbs. in aluminum heads. Likewise, 18 mm plugs with gasket style seats should be tightened to 32 to 38 ft.lbs. in cast iron heads but only 28 to 34 ft.lbs. in aluminum heads. For taper seat spark plugs, 14 mm plugs should be tightened to 7 to 15 ft.lbs. in both cast iron and aluminum, while 18 mm taper seat plugs should be tightened to 15 to 20 ft.lbs. in both types of heads.
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SPARK PLUG GAP As for setting the plug gap, always follow the vehicle manufacturer recommendations. Spark plug gaps typically range from .028 inches up to .034 inches or even larger. One exception here is Bosch Platinum+4 or Platinum+2 spark plugs. These plugs are pregapped at the factory to a standard 1.6 mm gap and should NOT be altered regardless of what the vehicle manufacturer specifies for the engine. Bosch says this is necessary to achieve maximum plug performance and longevity, so do not change the gap. The following spark plug gapping video is courtesy of NGK spark plugs:
Finally, play close attention to the condition of the spark plug cables and boots when changing the plugs. Loose fitting boots or damaged cables can cause ignition misfire. If your engine has a coil-on-plug ignition system, replacing the rubber boot that fits between the coil and spark plug is recommended when changing high mileage spark plugs. This will prevent arcing that can cause misfires. On engines with a distributor or a DIS coil pack, make sure the spark plug wires are properly routed to the correct cylinders (look up the firing order if it is not marked on the cabled). Plug wires must also be supported in their looms to avoid crossfire problems and contact with the hot exhaust manifold.
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More Spark Plug & Ignition Articles: Spark Plug Technology Why Spark Plugs Still Need To Be Replaced Spark Plug Fouling Original Equipment Spark Plugs, Are They Best? Don't Use Ordinary Spark Plugs with Waste Spark DIS Ignition Systems Spark Plug Wires Analyzing Ignition Misfires Spark Plugs & Ignition Performance Distributor Ignition Systems
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Why Spark Plugs Need To Be Replaced Copyright AA1Car One of the leading causes of hard starting is fouled or worn spark plugs. When a fuel injected engine that normally starts quite easily has to be coaxed to life, it often means the spark plugs are overdue for a change. As the electrodes wear, the voltage required to jump the gap and ignite the fuel mixture goes up. At the same time, accumulated deposits on the insulator can drain off voltage before it even has a chance to form a spark. So the engine fails to start or starts only reluctantly after prolonged cranking. One of the reasons why spark plug sales take off when cold weather arrives is because many motorists put off changing the plugs until they absolutely have to. The spark plugs continue to rack up mile after mile until they have deteriorated to the point where they are causing noticeable starting and driveability problems. Emission checks will catch a lot of bad spark plugs and force motorists to change plugs that need to be replaced. But in areas where emission checks are not required, the only incentives for changing the spark plugs are the driveability problems created by the plugs themselves. So many motorists today think they are saving money on maintenance by putting off a spark plug change until it is obvious the engine needs new spark plugs. Then and only then will they begrudgingly spend any money on a new set of spark plugs.
WHY CHANGE SPARK PLUGS? What motorists need to know is that spark plugs do NOT last forever, even the long-life 100,000 mile plugs. All spark plugs need to be changed sooner or later. Here's why: REASON #1 To Replace Spark Plugs: New plugs maintain peak engine performance and efficiency. Every engine will misfire occasionally. But as the number of misfires per mile goes up over time, it increases exhaust emissions, wastes gas and reduces power. In the past, most motorist would not notice the gradual decline in ignition performance until it reached a point where it created a steady miss, caused the engine to run rough, buck or stall, or made it hard to start. Not so today. All 1996 and newer vehicles have an OBD II onboard diagnostic system that tracks ignition misfires. When the rate of misfires exceeds a certain limit and causes emissions to increase 50% over baseline levels, it illuminates a warning light. Too bad older vehicle do not have this watchdog system. So on older vehicles, replacing the spark plugs at the recommended service intervals for preventive maintenance will reduce the risk of misfires and maintain peak engine performance. For standard spark plugs, the service interval is typically every 45,000 miles. For platinum spark plugs, it is 100,000 miles. A new set of plugs is not a cure-all for driveability and emissions problems, but in many cases a plug change can make a significant improvement. Changing the plugs can reduce hydrocarbon (HC) emissions up to several hundred parts per million, which may make the difference between failing and passing an emissions test.
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REASON #2 to Replace Spark Plugs: New plugs improve cold starting. Bad plugs are often responsible for many cold weather "no start" service calls. Many times the battery has been run dead while cranking the engine because the plugs would not light the fire. When the old plugs are removed and examined, they are often found to be worn or dirty. Dirty spark plugs can cause fouling which results in misfiring. For more info on this subjct, see Spark Plug Fouling. New plugs reduce the voltage requirements on the ignition system, which decreases the chance of misfire while leaving more amps for the starter and injectors. Wet fouled plugs can also prevent an engine from starting, but in many instances the fouling problem has nothing to do with plug wear or neglect. If an engine is flooded with fuel while it is being cranked, gasoline can soak the plugs and bleed off the ignition voltage before it forms a spark. Wet fouling tends to be more common on older vehicles that have carburetors because pumping the gas pedal can easily flood the engine with too much fuel. Flooding can also occur if the choke sticks, the float is set too high or the needle valve leaks. On fuel injected engines, wet fouling is less of a problem but can happen if a cold start injector leaks or there is a fuel calibration problem that creates an overly rich startup mixture. The cure in all cases is to wait for the plugs to dry out, or to remove the plugs and clean or replace them.
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REASON #3 to Replace Spark Plugs: New plugs minimize the risk of catalytic converter failure. A single misfiring plug can dump enough raw fuel into the exhaust to overheat and damage the converter. The presence of higher than normal quantities of unburned gasoline in the exhaust will cause the operating temperature of the converter to soar, which may lead to a partial of complete meltdown of the converter substrate. This, in turn, may form a partial restriction or complete blockage in the exhaust that creates enormous backpressure and chokes off the engines ability to exhale. The engine may lack power, especially at higher speeds, and deliver terrible fuel economy. Or, it may stall and refuse to run after it is first started. Replacing the converter will solve the restriction problem. But unless the spark plugs are replaced, the new converter may soon die from the same ailment.
ABOUT SPARK PLUGS P> The spark plugs are the business end of the ignition system. Whether an engine has a conventional distributor or a direct ignition (distributorless) system, a good set of plugs is absolutely essential for peak performance. The typical spark plug needs anywhere from 5,000 to 25,000 volts from the ignition coil before it will fire. The exact firing voltage depends on: Plug gap The wider the gap, the higher the voltage required. The gap must be set to specs for good ignition performance. Electrode condition Wear increase voltage requirements. Fouled electrodes may not fire at all! Engine load Higher load increases voltage needed. If the plugs are worn or gapped to wide, they may misfire under load.
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Resistance Electrical resistance in the plugs and wires increases voltage required. Replacing worn, damaged or loose fitting plug wires is recommended for improving ignition reliability. Operating temperature A cold plug requires more voltage to fire than a hot one. Reliable ignition, therefore, requires a hot spark from the coil, good plug wires to carry the juice, and spark plugs that are clean, in good condition and gapped properly. If any of these criteria are not met, the spark may not reach it intended destination causing the engine to misfire. One way to tell if the plugs need changing is to look at a vehicle's odometer. If it has been more than the recommended number of miles (usually 30,000) since the spark plugs were last changed, it is time for a new set. Another way to tell is to observe the secondary ignition pattern on an oscilloscope. If there is an open plug or wire, the plug will not fire causing the firing voltage to shoot up to the maximum output of the coil. Badly worn plugs or plugs that have been misgapped too wide will also increase the firing voltage dramatically (as can a bad rotor and/or ignition cables with excessive resistance). If the required voltage exceeds the maximum output of the system, the plugs may not fire. If the pattern shows initial secondary spikes approaching the upper voltage limits of the system, therefore, it is a sure sign that the plugs (and/or cap, rotor and cables) need attention. A fouled plug (or shored ignition cable), on the other hand, will show an unusually low firing voltage. Firing voltages should not vary by more than 3 kV cylinder to cylinder. A cylinder that shows an abnormally low firing voltage probably has a grounded spark plug (deposits bridging the electrode gap), or a shorted ignition cable. A cylinder that shows an abnormally high firing voltage compared to the others likely has an open ignition cable or a plug with a wide gap. The plug firing time (spark firing line) portion of the secondary ignition display shows the duration of the spark in milliseconds (thousandths of a second). The average spark duration with the engine idling should be about 1.5 milliseconds. A duration of less than 0.8 milliseconds would mean there either is not enough voltage to keep the spark going (low coil output), or the voltage is having trouble reaching its destination (excessive resistance in the plug wires). A longer than normal spark (1.8 milliseconds or more) is an indication that the firing voltage is experiencing little resistance because a plug is fouled or grounded (or a plug wire is shorted) probably due to accumulated carbon deposits. Fouling can be a problem if a plug's heat range is too cold for the application (which can be solved by installing hotter plugs). But it may also be the result of excessive oil consumption due to worn valve guides or seals, worn rings, or even short trip stop-and-go driving. Intermittent misfires can be caused by a variety of ignition, fuel or mechanical problems. Lean misfire occurs when there is too much air and not enough fuel, so the engine should be checked for air or vacuum leaks, dirty injectors, carburetion problems or a leaky EGR valve. If the misfire appears to "jump around" from cylinder to cylinder, a manifold vacuum leak or a leaky EGR valve may be the cause. But if the misfire is isolated to a single cylinder, a worn or fouled spark plug (or bad plug wire) is the most likely cause.
READING SPARK PLUGS
Click on image at left to view Spark Plug Diagnosis Chart. Examining the tips of the spark plugs as they are removed can reveal a great deal about the health and performance of an engine. The appearance and color of the deposits can reveal other problems that may need fixing: Normal deposits Light brown or tan colored. Fuel fouled spark plug Black fluffy carbon deposits indicate an overly rich fuel mixture or possibly a weak spark. Check for such things as a stuck choke, a heavy or misadjusted carburetor float, a leaky needle valve in the carburetor, leaky injectors, low coil output or high resistance in the plug wires.
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Wet spark plug A wet spark plug means the plug has not been firing. If not due to engine flooding, the problem may be a bad ignition cable (excessive resistance, shorted or arcing). But wet fouling can also be caused by dirt or moisture on the outside of the plug that provides a conductive path to ground, or by an internal crack in the ceramic insulator that shorts the plug to ground. Oil fouled spark plug Heavy black deposits with an oily appearance. These are the result of oil entering in the combustion chamber, probably past worn valve guides, guide seals or rings. Switching to a hotter plug may help prolong plug life somewhat, but no spark plug will survive long under such conditions. The only permanent cure to this condition is to fix the oil consumption problem. Glazed spark plug Yellowish melted appearing deposits on the insulator tip that result from high temperature operation. The engine may be running too hot (check for cooling problems), the EGR valve may be inoperative and/or the heat range of the plug may be too hot for the application. Switching to a cooler plug may be necessary if no other problems are found. Damaged plug If the electrodes have been smashed flat or broken, somebody put the wrong plug in the engine. A plug that protrudes too far into the combustion chamber may hit the piston or a valve. Always follow the plug manufacturers application recommendations when selecting replacement plugs to prevent this kind of problem. Overheating If the spark plug insulator is blistered, white and free from deposits, something is making the plug run too hot. If the heat range is not too hot for the application, check for cooling problems, incorrect ignition timing or a lean fuel mixture. Melted electrode A symptom of severe preignition. The spark plug has been running too hot for a long time (see overheating above). This can be very damaging and may burn a hole through the top of a piston! Detonation If the insulator is split or chipped, detonation (spark knock) may be occurring in the engine. The underlying cause here might be an inoperative EGR valve, overadvanced ignition timing, excessive compression due to accumulated deposits in the combustion chamber, or engine overheating.
SPARK PLUG REPLACEMENT TIPS When spark plugs are replaced, you might want to upgrade to a premium long-life platinum or iridium plug. These plugs cost a little more initially, but can actually save you money in the long run because they do not have to be replaced as often. Many of these plugs can go 100,000 miles or more. Such plugs would be a good choice for any vehicle where access to the spark plugs is a problem. Another option is upgrading to "performance" spark plugs. These plugs typically have unique electrode configurations that increase spark exposure to the air/fuel mixture and have multiple edges to reduce the chance of misfire. Performance spark plugs are usually more expensive than standard or even long-life plugs, but may be a good alternative if you want the ultimate in ignition performance. There are also spark plugs today that are specially designed for truck engines. Such plugs have increased fouling resistance and oversized electrodes for longer service life.
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More Ignition Related Articles: Spark Plug Technology Spark Plug Fouling Don't Neglect the Spark Plugs
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Spark Plug Fouling Copyright AA1Car Spark plug fouling is a common cause of engine misfire. When a spark plug becomes fouled for any reason, the spark plug will fail to fire and ignite the air/fuel mixture. This causes a misfire, a loss of power and fuel economy, and an increase in tailpipe hydrocarbon (HC) emissions.
Why Spark Plugs Get Dirty and Misfire Spark plugs are designed to be self-cleaning up to a point. When the engine is running, the ceramic shell that surrounds the center electrode gets hot and helps to burn off any fuel or oil ash deposits that might otherwise foul the spark plug. The "heat range" of the spark plug determines its operating temperature and its built-in fouling resistance. The plugs should be hot enough to prevent fouling but not so hot that they increase the risk of preignition and detonation. The spark plugs that are specified for your engine by the spark plug manufacturer should be correct for your vehicle application. Full throttle acceleration and highway driving is good for spark plugs because it generates heat that helps keep the spark plugs clean. Short trip stop-and-go city driving and prolonged idling, on the other hand, are NOT good for the plugs because the plugs may not get hot enough to burn off all of the deposits. So as deposits accumulate, the risk of misfire goes up. And if the plugs get dirty enough, they will misfire. The electrical energy from the ignition coil that normally creates the spark will short circuit to ground across the deposits on the center electrode instead of jumping across the electrode gap to ignite the air/fuel mixture.
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Deposits on the center electrode create a ground path for the spark , causing a flashover misfire if the plug is dirty. On 1996 and newer vehicles with OBD II, spark plug misfiring will usually turn on the Check Engine light and set one or more P030X misfire codes where "X" is the number of the cylinder that is misfiring. Your vehicle will NOT pass an emissions test with a Check Engine light on or misfire codes present.
Quick Fix for Fouled Spark Plugs If your spark plugs are fouled and misfiring because you have been driving your vehicle infrequently, or you have only been driving short distances (only a few miles per trip), or you have been letting your engine idle for long periods of time (15 minutes or more), try this: Take your vehicle out on the highway, accelerate quickly and drive it at highway speeds for 15 to 20 minutes. This should clean the plugs if the cause of the fouling is nothing unusual. If the spark plugs continue to misfire because of fouling, they may be dirty or worn. Remove and inspect the spark plugs, and either clean or replace them as needed. Auto Parts stores sell spark plug cleaner devices that sand blast the end of the spark plug to remove deposits. If you use one of these devices,make sure no sand remains trapped between the spark plug electrode and shell before they go back in your engine. Also, be sure to regap the spark plug electrode gap back to specifications (which requires a spark plug gapping tool or feeler gauge). The recommended gap is usually specified on an underhood emissions decal in the engine compartment. Reading the spark plugs can tell you why they are fouling:
Click the image to view the spark plug chart.
If the spark plugs are really dirty, worn or you don't want to try cleaning them, throw the old plug in the trash and install a new set of spark plugs. Make sure the spark plugs are the correct number for your engine application, and that they are gapped correctly. Most spark plugs are pregapped, but the gap may not be correct for your engine application. If you can't avoid a lot of idling or short trip driving, refer to the spark plug supplier's catalog for a spark plug that is one heat range HOTTER than the standard spark plugs specified for your engine. Increasing the heat range slightly can improve fouling resistance by helping the plugs run hotter.
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If you have a modified performance engine, however, you might want to install spark plugs that are one heat range COLDER than the standard spark plugs that are specified for your engine. High performance engines produce more heat and are at greater risk of engine-damaging detonation, so going with a slightly colder spark plug is often recommended to reduce the risk of detonation. The trade-off, however, may be an increased tendency to foul if the engine is idled too long or only driven at slow speed (as when driving around at a cruise night event).
CAUSES OF SPARK PLUG FOULING If your spark plugs are fouling and keep fouling out, you probably have an engine problem. Normal spark plug deposits are typically light tan or brown in color. Black deposits or heavy ash deposits usually indicates trouble. Some common causes of spark plug fouling include: Worn or damaged valve guides or valve guide seals. Problems here can allow oil to dribble down the valve stems and enter the combustion chamber. Oil will form heavy black wet oily deposits on the spark plugs. Worn or damaged piston rings, or worn or damaged engine cylinders. Badly worn piston rings, broken or cracked piston rings, grooves or scoring in the cylinder walls, or even piston rings that have been installed upside down can allow oil to get into the combustion chamber and foul the spark plugs. Rich fuel mixture. This will produce black fluffy deposits on the spark plugs. If only one or two spark plugs are affected, the underlying cause may be a leaky fuel injector. If all of the spark plugs show heavy dry carbon fouling, the rich fuel mixture may be caused by too much fuel pressure (check for a defective fuel pressure regulator or a plugged fuel return line). A defective oxygen sensor that reads lean all the time can also make the fuel mixture run rich. Check fuel trim readings with a scan tool to see if the engine is running rich (negative fuel trim numbers that are -8 to -10 or more would tell you the engine is running rich). On an older carbureted engine, a rich fuel mixture can be caused by a leaky float, incorrect float setting inside the fuel bowl, a leaky fuel inlet needle valve, or incorrect jetting (too large). Leaky Head Gasket. This is really bad news because a leaky head gasket can be very expensive to repair. If coolant seeps into the combustion chamber, it will form fouling deposits on the spark plug. A fouled spark plug may be an early sign that a head gasket is starting to leak. The cheap fix here wold be to add a bottle of cooling system sealer or head gasket sealer to
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the cooling system and hope it seals the leak - at least temporarily.
Coolant leak s into the combustion chamber can cause this type of spark plug fouling.
WET SPARK PLUGS Wet spark plugs means the spark plugs are not firing. The spark plugs are coated with unburned gasoline, which allows the ignition voltage to short circuit to ground instead of jumping across the electrode gap normally. Wet fouled spark plugs can be caused by flooding the engine when attempting to start a cold engine. This was a common problem on older carbureted engines and could be caused by pumping the accelerator pedal excessively, a choke that was sticking shut, or internal carburetor problems such as a bad float or leaky inlet valve that allowed too much fuel into the engine. With fuel injected engines, flooding is seldom a problem unless one or more fuel injectors are leaking, there is excessive fuel pressure, a cold start injector valve is stuck on, or the EVAP system purge valve is stuck open allowing fuel vapors from the charcoal canister to be sucked into the engine. Pumping the accelerator pedal on a fuel injected engine does nothing, but holding the pedal all the way to the floor will usually cause the engine management system to go into the "floor clear" mode while the engine is cranking. This temporarily cuts off the fuel supply to the engine so it will pull in more air and hopefully help dry the wet spark plugs. Ignition problems can also cause wet spark plugs. If the spark plug wires or ignition coil(s) are bad, the plugs won't fire the air/fuel mixture. On engines with individual coil-over-plug ignition systems, arcing between the coil boot that fits down over the spark plug can short the spark to ground and cause misfiring and wet spark plugs. A bad crankshaft position sensor that is not generating an ignition pulse signal can also prevent the spark plugs from firing. The fix for wet spark plugs (assuming there are no underlying ignition coil, plug wire or crank sensor problems) if often just to wait and try starting the engine again later. Spraying some starting fluid (ether) into the throttle body and cranking the engine may get the fire going and dry the plugs. The spark plugs can also be removed and air dried, but that's a pain on many modern engines.
More Ignition Related Articles: Why Spark Plugs Need to be Replaced Spark Plug Technology Don't Neglect the Spark Plugs Original Equipment Spark Plugs, Are They Best? Ford Motorcraft Spark Plug Breakage Problem (2004 - 2008 Ford Trucks w/5.4L V8, & 2005 - 2008 Mustang GT with 4.6L V8) Bosch Platinum +4 Spark Plugs Don't Use Ordinary Spark Plugs with Waste Spark DIS Ignition Systems Spark Plug Wires Analyzing Ignition Misfires Spark Plugs & Ignition Performance Distributorless Ignition Systems Coil-Over-Plug Ignition Systems http://www.aa1car.com/library/spark_plug_fouling.htm
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Original Equipment Spark Plugs Copyright 2010 AA1Car When you change your spark plugs, should you use the same brand and part number as the original, or a different brand? Most professional technicians say they usually replace same with same, unless there is a reason to install a different brand of spark plug. If you use the same spark plug that the engine came equipped with from the factory, you should not have any problems with spark plug Fouling, misfiring , detonation or preignition. When a vehicle manufacturer chooses a certain spark plug for an engine, the plug has to undergo extensive validation testing to make sure it does not run too cold and foul, or run too hot and cause detonation or preignition, or suffer misfiring due to electrode position or wear. Most original equipment spark plugs today are platinum or iridium and have a recommended replacement interval of 100,000 miles. So the validation testing is designed to simulate that kind of mileage before the plug receives its stamp or approval.
SPARK PLUG BRANDS Years ago, most vehicle manufacturers used only one brand of spark plugs in their engines: AC Delco in GM engines Motorcraft or Autolite in Ford engines Champion in Chrysler engines Bosch in European makes NGK or DENSO in Asian makes
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In most cases the vehicle manufacturer either owned the spark plug supplier, or had a long historical relationship with that supplier. But globilization and competition has changed that once-cozy relationship. Today, you may find some GM or Ford engines factory-equipped with Bosch spark plugs, Mazda engines equipped with Motorcraft spark plugs, Chrysler engines equipped with NGK or DENSO spark plugs, and so on. Most late model Saturn engines use NGK spark plugs. Kia and Hyundai may come factory-equipped with either NGK or Champion spark plugs. Some vehicle manufacturers still rely on a single spark plug supplier, but most use a mix of suppliers, even for the same engine. For example, a late-model Chrysler V6 may come factory equipped with a Champion spark plug, a NGK spark plug or a DENSO spark plug. All are "factory approved" for the application, so which plug is used on any given day may depend where the engine is assembled, which supplier shipped the vehicle manufacturer a container of spark plugs that day, and so on.
MOST BRANDS OF SPARK PLUGS HAVE PLUGS FOR ALL MAKES/MODELS Here’s something else many people don’t know. Most spark plug supplies sell a full line of spark plugs that fit most makes and models, not just the applications where they are the original equipment supplier. What’s more, many spark plug suppliers buy spark plugs from each other for applications they do not manufacture themselves. Why? So they can offer a broader product line with more complete coverage. Consequently, most spark plug suppliers catalogs list many vehicle applications for which they were not the original equipment supplier. They also have cross-reference indexes in the back that help you figure out which of their spark plugs can be used to replace another brand of spark plugs.
Peak ignition performance requires a reliable spark with no misfires.
WHICH BRAND OF SPARK PLUG IS BEST FOR YOUR ENGINE? Here is another fact some people have a hard time digesting: No one brand of spark plug is superior to any other brand. This does not mean any brand of spark plug will work in any engine. The heat range of a replacement spark plug (ANY brand) must be a close match with the original spark plug (ANY brand) for good ignition performance. The electrode configuration can be different as can the materials used to make the electrodes, but the electrode gap(s) must not be too wide or too narrow for the air/fuel mixture or firing voltage capabilities of the ignition system. The electrodes on the replacement spark plugs should also be capable of lasting at least as long as the original spark plugs. The best advice we can offer is to use the same brand and type of replacement spark plug as the original spark plugs that came in your engine, unless you want to upgrade standard plugs to long life platinum or iridium spark plugs. If the spark plugs have already been replaced at least once in your engine, and you are not sure they are the same brand as the original, or you don’t know what brand the original plugs were, ask an auto parts store employee to look up the plugs for you in their data base. Most list the original equipment spark plug along with any other brands the store carries that may also fit your engine. If you want a certain brand of spark plug , but the spark plug manufacturer does not list one of their spark plugs for your engine, there is a reason why. Either they do not make a plug that fits your engine, or the plugs they have do not have the correct heat range or electrodes for your engine.
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DO NOT try to match plugs by visual appearance. Two different brands of spark plugs that seem to be identical on the outside (same diameter and thread pitch, same type of electrodes, same length) may have differences inside that create a significant difference in heat range.
UPGRADING SPARK PLUGS Upgrading from standard spark plugs to platinum or iridium spark plugs usually makes sense in many instances, but downgrading from platinum or iridium to a standard plug does not unless you have a reason for changing plugs frequently (such as an engine that burns oil).
INSTALLING THE WRONG SPARK PLUGS Replacement spark plugs must have the same physical dimensions as the original to fit the cylinder head. The thread diameter, pitch and seat configuration must be identical. The "reach" of the electrode (how far it protrudes into the combustion chamber) must also be similar to avoid mechanical interference with the pistons or valves. The replacement spark plug must also have a heat range that is similar to the original spark plugs. If the wrong replacement spark plug (ANY brand) is installed in an engine, the spark plugs may experience rapid fouling and misfiring (if the replacement plug is colder than the original), or preignition and/or detonation (if the replacement plug is hotter than the original), or possible misfiring due to electrode erosion or metal transfer. For example, the best type of park plugs for "waste spark" distributorless ignition systems are ones with double platinum (platinum on BOTH the center and ground electrode), or iridium on the center electrode and a hard alloy on the outer ground electrode, or multiple ground electrodes.
Watch Out for Ford Motorcraft Two-piece Spark Plugs That Break! The original equipment Motorcraft brand spark plugs that were factory installed in many late model (2004 to 2008) Ford trucks with 5.4L V8 and 6.8L V10 engines, 2005 to 2007 Mustang GT 4.6 & 5.4L V8 engines, and 2008 Mustang GT models built prior to 11/30/07) can break when you attempt to remove them! The spark plugs have a crimped lower electrode shell that becomes coated with carbon, causing it to stick in the cylinder head. When you attempt to unscrew the plug, the lower shell breaks off and stays in the head. Removing the broken shell requires a special Ford, Snap-On or Lisle extractor tool. Worse yet, if any shell or electrode fragments fall into the cylinder and can't be fished out, you may have to remove the cylinder head to get the debris out. Many experts recommend replacing the original equipment Motorcraft spark plugs before the get too many miles on them (over 35,000). Replacing the plugs at low mileage will reduce the risk of them sticking and breaking. Waiting until the original equipment spark plugs have 100,000 miles on them is asking for trouble! Ford Technical Service Bulletin 08-7-6 covers the recommended removal procedure for these spark plugs, as well as the repair procedure if one or more plugs break ( Click Here to View Ford TSB 08-7-6). Essentially, it says to remove the spark plugs when the engine is COLD (room temperature). Loosen the plugs about 1/8 to 1/4 turn, stop and spray some WD-40 or penetrating oil into the spark plug well. Allow the oil to soak into the threads so it can loosen the carbon around the electrode shell. Wait at least 15 minutes, or longer (overnight is recommended if the plugs have over 80,000 miles on them). Then slowly loosen the plugs, applying no more than 35 ft. lbs of torque to your wrench. If a plug sticks, retighten it half a turn, apply more penetrating oil, wait, then try again. Do NOT reinstall the same Motorcraft spark plugs (PZT 2FE Platinum). Replace them with a much improved one-piece spark
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Original Equipment Spark Plugs
plug from Champion (7989), or a similar spark plug from NGK, Denso or Bosch. Apply nickel anti-seize to the outer surface of the lower electrode shell (the smooth part) before installing the plugs. For more information about the Ford spark plug breakage problem Click Here.
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