Types of Fuel Pump Pressure Tests
A proper fuel pressure system test determines the amount of pressure in the fuel system and checks for defective fuel pump. Depending on the application, the fuel system may require 30-80 psi of fuel pressure to start and run. Pressure specifications are different and depend on the type of fuel injection system as well as the fuel economy, engine performance and emission requirements.
Fuel pressure test is done in different ways as follows: Static fuel pressure test: It is a test used to measure the sustained pressure (PSI) recommended by the manufacturer. It can be performed by simply energizing the pump via the key switch or by connecting to an auxiliary battery. If the fuel pump is energized it will rise the fuel pressure quickly and holds steadily at a fixed value in the absence of voltage at the pump.If the pressure reading is lower than normal the cause can be, a blockage in the fuel line, a weak pump, tank or filter inlet sock or a faulty pressure regulator.
Residual fuel pressure test: After the completion of static fuel pressure test, the fuel pump stops running or is turned off, At this point the system should hold the residual pressure for few minutes. If the pressure drops down quickly, it indicates that the vehicle may have a leaky fuel pump. Check valve, fuel line, fuel injectors or a fuel pressure regulator. A low residual fuel pressure can cause vapor lock or difficulty in starting during hot weathers.
Running fuel pressure test: This test is performed by Idling the engine and comparing the gauge reading to specifications. If the pressure is low it indicates the pump is either weak or with low voltage, clogged fuel filter, bad fuel pressure regulator or an empty fuel tank.
Dead head pressure test: This test checks the maximum output pressure of the fuel pump. When the return line is shut down, the pump should produce double times the normal operating pressure at idle. In case, if the pump fails to go up it may not be able to deliver sufficient fuel at high engine speeds. The causes of this failure may include low voltage at the pump, a worn out pump or an obstructed fuel line etc.
Fuel volume test: A fuel pump test is one of the best ways to evaluate the pump's condition in which the volume of the fuel delivered is measured over certain time period. Fuel pump though delivers normal pressure still causes driveability issues if it is unable to deliver enough fuel volume to meet the engine's need. The main causes of low delivery fuel volume include a plugged fuel filter, a worn fuel pump or an empty tank.
Fuel pressure drop test: this test measures the fuel pressure drop in static system when each injector is energized. The extent of pressure drops for every injector is checked and if the difference is more than 3 PSI it indicates that injectors are dirty and needs to be replaced or cleaned.
Fuel pressure regulator test: This test checks the pressure regulator operation to ensure that it changes line pressure with respect to changes in engine vacuum. It is necessary to maintain accurate operating pressure behind the injectors to reimburse for changes in engine load. In case if the fuel pressure is less than the manufacturer's specifications the engine experiences stalling problems.
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