Part 1 of 3

Chart A-7 Diagnostic Chart (Part 1 Of 3):

Fuel System Pressure Test:

Fuel System Description:

An electric fuel pump, part of the modular fuel sender and located inside the fuel tank, pumps fuel through an in-line filter to the fuel rail assembly. The pump is designed to provide fuel at a pressure above the regulated pressure needed by the injectors. A pressure regulator, attached to the fuel rail assembly, keeps fuel available to the injectors at a regulated pressure. Unused fuel is returned to the fuel tank by a separate line. The fuel pump test connector is located in the engine compartment. When the engine is stopped, the pump can be turned "ON" by using a fused jumper wire to apply battery voltage to the test connector.

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

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

Test Description: Number(s) below refer to circled number(s) 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.
With ignition "ON," engine "OFF," fuel pressure should be 284-325 kPa (41-47 psi). This pressure is controlled by spring pressure and manifold vacuum within the pressure regulator assembly. Pressure should not leak down after the fuel pump is shut "OFF."
2. When the engine is idling, the engine vacuum is high and is applied to the fuel regulator diaphragm. This will offset the spring and lower fuel pressure approximately 21-69 kPa (3-10 psi).
3. The application of 12-14 inches of vacuum to the pressure regulator should result in a fuel pressure drop of at least 21-69 kPa (3-10 psi).
4. Pressure that leaks down may be caused by one of the following:
^ Leaking fuel pump feed hose.
^ Leaking check valve within fuel pump feed hose.
^ Fuel pressure regulator valve leaking.
^ Injector(s) sticking open.