Part 1 of 2

Fuel System Pressure Test (Part 1 of 2):

Fuel System Circuit Diagram:

CIRCUIT DESCRIPTION:

The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled to 245 to 256 kPa (35 to 38 psi). Excess fuel pressure is returned to the fuel tank. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to the test terminal located in the engine compartment.


TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Use pressure gage J-34730-1. Wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gage. Pressure should not leak down after the fuel pump is shut "OFF."

2. When the engine is idling, the vacuum is high and, if applied to the fuel regulator diaphragm, will offset the spring and result in a lower fuel pressure, 190-200 kPa (25-30 psi).

3. The application of vacuum to the pressure regulator should result in a fuel pressure drop.

4. Pressure that leaks down may be caused by one of the following:

^ In-tank fuel pump check valve not holding.
^ Pump coupling hose leaking.
^ Fuel pressure regulator valve leaking.
^ Injector sticking open.


DIAGNOSTIC AIDS:

Improper fuel pressure may contribute to one or all of the following symptoms:

^ Cranks but won't run
^ May set Code 44 or 45
^ Cuts out, may feel like an ignition problem
^ Hesitation, loss of power or poor fuel economy