New technology affects service practices

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GM EcoTec3 truck engine GDI concerns

New technology affects service practices

GM’s EcoTec3 engines are workhorses, built for the tough stuff such as delivering power for hauling. This technology will increasingly be showing up in your bays, so here’s what you’ll need to know about servicing GDI (gasoline direct injection) technology. Get them back on the road, and your customers will appreciate the increased fuel mileage, power output, torque and engine longevity.

By Jeff Taylor

General Motors’ EcoTec3 family of engines is a familiar sight under the hoods of many GMC and Chevrolet pickup trucks and SUVs. It is available in three versions: 4.3 V6, 5.3 V8 and a 6.2 V8. General Motors debuted this new engine design on the 2014 model year trucks and although the 6.2 V8 versions look comparable to the GEN 5 V8 LT of the Corvette and Camaro, they are uniquely individual engines. The EcoTec3 was designed with towing,

hauling and pickup truck grunt work in mind, not pulling 1G on the skid pad. The EcoTec3 engines introduced a tremendous amount of new technology for a truck engine and involved major internal architecture changes over its V6 and V8 predecessors.

These new technologies and design changes were needed to achieve increased fuel mileage and reduced emissions output while raising power output, torque and increasing engine longevity. Compression ratios increased, intake and exhaust valves swapped locations in the cylinder head, spark plug angles changed to provide better electrode placement in the combustion chamber, a special lubrication system was designed and the engines’ fuel delivery system changed. The EcoTec3 engine was equipped with gasoline direct injection, or GDI, replacing the old port style fuel injection used in different versions for many years. GM had been using GDI in other vehicles for some time, but this was their first use of GDI in full-sized pickup and SUV applications.

Directly injecting the fuel into the cylinder optimizes combustion over a wide range of operating conditions, allows for increased

compression ratios without knock and providThe low-pressure system ing increased power output and fuel economy The low-pressure system is responsible for with lower emissions. The use of GDI helped moving the fuel from the fuel tank to the reduce cold start hydrocarbon emissions by high-pressure fuel pump, and the EcoTec3’s 25% on the EcoTec3 series of engines. For all low-pressure fuel system is electronically conthe positives that GDI achieves it has also trolled and return-less. GM uses a modular created some diagnostic, service and safety reservoir assembly (MRA) that houses the fuel challenges that today’s techs should be aware pump, fuel pressure regulator, filter assembly, sending unit and a jet pump that uses some of the fuel pump’s pressurized output to maintain the proper fuel level in the MRA. The low-pressure system utilizes a fuel pump control module (FPCM) to control the low-pressure fuel pump operation. The powertrain control module (PCM) monitors and requests low-pressure fuel pump operation using the GMLAN serial Shown here is the General Motors 4.3 V6 EcoTec3 engine version. data line connected to the of before performing service on them. These FPCM. The FPCM then controls the fuel trucks and SUVs are popular and many are pump speed and the desired fuel pressure starting to show up at our shops with fuel requested by the PCM using a 25 kHz pulse system-related issues. No-starts, driveability width modulated (PWM) control signal. The glitches, illuminated malfunction indicator maximum current that the can be supplied to lamp (MIL) and other fuel system-related the in-tank fuel pump from the FPCM is 22 concerns are common and when that happens A. A serviceable inline fuel pressure sensor you are going to need a plan of attack for (three wire, five volt sensor) mounted on the efficient diagnostics. output fuel line from the fuel tank reports

That plan starts with understanding how low-pressure fuel system information to the the EcoTec3’s GDI fuel system functions FPCM so that it can maintain the pressure and breaking it down into three distinctive desired PCM commanded pressure. The fuel systems: low-pressure, high-pressure and pressure will vary with load, but typical readinjection. Each system has its own operational ings at idle will be 43 psi to 45 psi and key on/ characteristics, and understanding those engine off values range from 50 psi to 100 psi characteristics is important for effective depending on operating conditions, temdiagnostics, repairs and personal safety. perature and other factors. The pressure will

increase to almost 90 psi to 100 psi during The high-pressure system initial cranking. The GDI system is injecting the fuel directly

The FPCM is used to lower the electrical into the combustion chamber and has a small system load on the vehicles and increase the window of opportunity to deliver it (more on fuel pump longevity by reducing the fuel this later) so it requires a fuel pressure that is pump speed when the engine is under low much higher than the old port fuel injection load situations. During heavy load or hard pressure values we are accustomed to dealing acceleration, the FPCM will increase the with. These high pressures are achieved using fuel pump speed as required to make sure a PCM-controlled mechanically actuated the engine gets the fuel needed. The FPCM high-pressure fuel pump assembly that is can store DTCs and it will instruct the PCM driven by a special three-lobed section on to turn on the MIL due to issues that are the camshaft. It is capable of a producing a under its control. Wiring to the low side fuel maximum 3,118 psi before the mechanical pressure sensor, circuit issues to the FPCM, internal relief valve opens. The normal operthe low-pressure fuel pump operation and fuel ating pressure range is lower, typically in the pressure concerns are just a few of the factors 290 psi to 2,176 psi range depending on what that can set DTCs. The FPCM can be easily the PCM is requesting to meet actual vehicle overlooked and is a major cause of no-starts operating conditions. The PCM regulates and stalling conditions, so it should always be the output pressure of the high-pressure fuel checked for trouble codes when diagnosing a pump by controlling an integral electronic fuel system concern. using a 12V PWM control signal.

Low-pressure concerns

GM started using the FPCM back on some full-size pickups in 2008, as corrosion Stainless steel and water intrusion of both fuel lines the connector and module Injectors have been an ongoing issue. The FPCM comes blank and needs to be programmed to function... it’s not plug and play. There were some factory manufacturing issues that installed the incorrect fuel pressure regulator inside the MRA resulting in hard starts, stalling and stumble concerns, and this repair requires a MRA High-pressure fuel pump replacement.

Some inferior quality aftermarket MRAs don’t have a jet pump and that can cause stalling and fuel starvation problems when the fuel level

The PCM regulates fuel pressure by opening is low or the truck/SUV is on High-pressure fuel uneven ground. It’s important pressure sensor to make sure the replacement An example of the EcoTec3 GDI high-pressure fuel rail assembly. It MRA is equipped with the jet shows the high-pressure fuel pump, high-pressure fuel pressure pump. sensor, stainless steel fuel rails, lines and injectors.

pressure side). This high-pressure sensor uses four wires and contains two analog pressure sensors and a 5V reference signal (this sensor is our window to the high-pressure side as there is not a test port). When the pressure is low, the output signal voltage is low and when the pressure is high the output signal voltage is high. The sensor is serviceable separately from the rail and the proper torque is required if replacement is needed. be followed carefully and all the proper safety precautions must be followed when any service is to be performed. Proper fuel depressurization procedures and personal safety equipment are essential as there is more than enough fuel pressure to cause serious harm.

High-pressure concerns

Proper depressurization is essential before any service can be performed on the high-pressure side and the service manual information This shows the inside of a GDI combustion chamber. You can see the will commonly tell you to intake and exhaust valves, spark plug and GDI fuel injector locations. remove the fuel pump fuse and closing this electronic pressure control it stalls work can be performed. But I have solenoid each time the piston is being stroked had these engines keep running! There can (three times per cam revolution) allowing for be enough pressure from the low-pressure the fine-tuning of the fuel pressure in the fuel side system to allow the engine to idle, and rail. The pressure control solenoid is normally run like it is in a limp-in mode. I hook up a closed or in the low-pressure mode and needs scanner and look at the high-pressure fuel to have a 12V control signal to increase the sensor value; it should show 100 psi or less fuel pressure (this is important to remember and I consider that a safe pressure to begin because a simple open circuit/damaged repairs. NOTE: If the high-pressure fuel connection could cause fixed low pressure pump has to be removed, the retaining bolts output). The high-pressure fuel pump is conhave to be replaced when reinstalling the nected to the fuel rail assemblies using two pump as the bolts are torque to yield. intermediate stainless steel fuel feed pipes. The cam needs to be set so that the pump is The fuel line on the left bank contains the fuel not in stroke (on the base circle, off the lobe) injection fuel rail fuel pressure sensor (GM’s before installation. The pump flange wasn’t name for the fuel pressure sensor on the highdesigned to pull the pump down over spring and start the engine. After

Great care must be taken when dealing This is a GDI injector. Note the carbon build-up on with the high-pressure side for safety reasons. the bottom seals that will need to be replaced and Proper service information procedures must resized if this injector was being reused.

pressure and may bend. There is a factory tool available to verify this position but I use a dial indicator and slowly rotate the engine to locate the off-lobe position. There is a pump roller bucket/follower underneath the pump’s actuator plunger that is indexed so make sure it is properly aligned before installation. Any time any of the high-pressure feed lines are removed or loosened, they need to be replaced. These feed pipes are single-use due to the slight distortion when tightened to give a proper seal, and during installation don’t use any sealer. Just a drop of clean engine oil is all that is needed. There are TSBs for noises, buzzing and vibration concerns from bad check valves and high-pressure fuel pumps that may give off a fuel smell or actually leak. Both require replacement of the high-pressure fuel pump assembly, mounting bolts and fuel line. Another concern is in the engine harness connector X161 at the rear of the engine. This connector provides the high and low side circuits to pressure control solenoid and it may blacken or corrode causing intermittent opens in the circuit (and low fuel pressure). The fuel pump diver lobe on the camshaft can suffer accelerated wear and scuffing from a lack of

These are photos of low-pressure fuel sensors. The top photo is a sensor on a 2017 GMC Tahoe. The lower photo shows a low-pressure sensor on a 2014 GMC Sierra. Both are three-wire sensors. maintenance, improper oil (they recommend

Spark Plug Tips Tell a Story

Here’s how to read it

Spark plug firing tips tell a lot about an engine. Their appearance will reflect both the performance of a well-tuned engine or conversely, one that’s been poorly maintained.

Spark plugs are easy to replace, cost effective and immediately improve engine performance. However, they are often ignored until problems arise. Bad plugs can lead to rough idling, power loss, poor fuel economy and excessive emissions. Make sure to change your spark plugs at the OE recommended service intervals.

“Reading” a spark plug is easy, requiring visual inspection of three key areas: the firing tip, the condition and color of the ceramic insulator, and the metal electrodes (known as the center wire and ground wire). If you have access to an Autolite® Master Catalog, you will find a series of pictures on the inside back cover to compare your spark plugs against. The color of the firing tip tells you:

• Light tan or gray deposits are normal and an indication that everything is working well. • If the tip is white with glazed deposits on the ceramic insulator, the spark plug is too hot for the engine or for the conditions in which it was used. • If black sooty deposits are present, a too rich fuel mixture is likely, or the spark plugs’ heat range may be too cold for the application. Check the Autolite catalog to be sure you have the correct part number and heat range. • Shiny black or oily deposits are an indication of bad oil seals and/or piston rings, and are not an indication that the spark plugs are at fault. When you change your spark plugs at OE recommended intervals, always use the metallurgy that is equal to or better than what is original equipment. It’s one of the most economic ways to maintain an efficient engine and avoid wasting fuel. As spark plug electrodes wear, the voltage required to jump the gap increases. Under hard acceleration, high speeds, or heavy loads, misfires can occur which result in a waste of fuel and a check engine light. Also, a rich fuel mixture or poor oil control can foul the ceramic insulator on the spark plug tip. Fouling, like excessive wear, will prompt misfires and can eventually cause the spark plug to stop functioning.

If you have any questions about how to read your spark plug or would like additional tips, let our Technicians help by calling 855-200-5200 or visiting www.Autolite.com. You can also order the latest Autolite catalog free of charge by calling our Distribution Center toll free at 1-800-890-2075.

FramGroup 1900 W. Field Court Lake Forest, IL 60045 847-482-2045 Brian.Kelley@framgrp.com www.framgrp.com Autolite® is the registered trademark of Fram Group IP LLC

Dexos) or if the engine is continually low on oil. It’s also important to remember that all of the extra sound deadening material and covers must be replaced after service, or a ticking/ lifter type noise complaint may result.

The high-pressure fuel injectors:

The EcoTec3 engine’s fuel injectors fire directly into the combustion chambers and this presented some problems for the engine’s designers. The injector tip must deal with the cylinder’s compression pressures, temperatures over 1,000 degrees Fahrenheit, fuel pressures in excess of 2,000 psi, deposit resistance and limited space to be installed. Engine design changes were needed. Special pistons, combustion chamber shape and a GDI fuel injector had to be developed to meet these conditions.

A low impedance, peak and hold injector was developed that could spray atomized fuel through laser-drilled holes directionally into a specially designed piston dome relief or

“fuel bowl” to maximize power and combustion efficiency. But getting these injectors to open under such extreme operating conditions requires more than 12V. The PCM was redesigned to incorporate an internal DC to DC converter boosting 12V to the needed 65V (stored in capacitors) to get these injectors to open. Once opened, 12V is all that is needed to hold it there. Providing the engine with the correct volume of needed fuel is another issue.

On a port fuel injector increasing the injectors’ on time worked, but that can’t happen with direct injection because it can only fire when the exhaust valve is closed.

Port style injectors had an on time of 1.5ms to 3.5ms and that is an eternity compared to the average GDI injector on time of only 0 .4ms. The volume of fuel delivered to each cylinder on these truck engines is now controlled by the fuel pressure. The higher the pressure, the more fuel that is injected. The PCM controls the high-pressure fuel pump’s electronic pressure control solenoid to maintain the proper fuel pressure available at the injectors and this provides the volume of fuel needed to meet the current operating conditions. Again, similar to dealing with the highpressure fuel pump and its components these injectors have enough fuel pressure and voltage to do serious harm, so be sure to follow all the proper safety and service precautions when working on or near them.

The FPCM is mounted in front of the spare tire exposed to all the elements and is a common cause of driveability or no-start concerns.

High-pressure injector concerns:

These injectors have a low resistance of 1.06 Ω at 68 degrees F, so any corrosion that increases the resistance anywhere

in the circuit will likely trigger issues and trouble codes. Attention to the noise deadening materials and its proper placement is important to limit comeback complaints. Because the injector tips are in the combustion chambers they are susceptible to carbon build-up, and this can prevent removal issues with potential damage (think Ford Triton 3V spark plugs). Applying penetration oil at the sealing surface and carbon remover solution inside that cylinder via the spark plug hole is a recommended procedure.

There are special puller tools that apply even pulling pressure along the entire fuel rail during removal to prevent damage to the injectors and the cylinder head. Any time the injectors are removed, the retainer clips holding them to the fuel rail, the plastic spacers and dust and combustion chamber seals and fuel feed pipe must be replaced. The combustion chamber seals require specific tools for installation and no lubricants should be used to install them. After installation on the injector body, the seals need to be resized to provide a leak-proof seal.

Using GDI and firing the fuel directly into

In this photo, note the three-peak lobe located at the rear of the camshaft. The tri-lobe provides the drive for the GDI fuel pump.

the combustion chamber certainly has its advantages, including better fuel economy, more torque and power from higher compression ratios and leaner cold start emissions. But it also has some disadvantages, including higher soot levels when cold, additional specialty tools, many single-use components and the issue of carbon on intake valves. Lack of proper maintenance, poor fuel quality and improper oils are all enemies of the GDI

This screen capture was taken during engine cranking on a 2015 5.3 V8. Note that the desired fuel rail high-pressure reading is at 1,870 psi (almost maximum), yet the low side is at 51.78 psi.

This screen capture features the same 2015 5.3L V8 and shows typical high and low side fuel rail pressure values at idle.

system. They can lead to accelerated wear and a host of other issues, but these systems are robust. Safety procedures and depressurization steps have to be followed and the use of 65V requires careful attention to detail before any back-probing of circuits is performed during testing.

The use of GDI in combination with other technologies like active cylinder management, variable valve timing and adaptive exhaust systems has made these engines and the trucks that use them smooth running, durable and reliable.

Jeff Taylor boasts a 32-year career in the automotive industry with Eccles Auto Service in Dundas, Ontario, as a fully licensed professional lead technician. While continuing to be “on the bench” every day, Jeff is also heavily involved in government focus groups, serves as an accomplished technical writer and has competed in international diagnostic competitions as well as providing his expertise as an automotive technical instructor for a major aftermarket parts retailer.