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Chart A-7:

Fuel Flow Circuit:

CIRCUIT DESCRIPTION:
When the ignition switch is turned to the "ON" position, the ECM will activate the in-tank fuel pump. The fuel pump will operate as long as the engine is cranking or running, and the ECM receives an ignition reference pulse. If no ignition reference exist, the ECM will shut "OFF" the fuel pump in about 2 seconds after ignition "ON" or 10 seconds after reference pulses stop. 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, keeps fuel available to the injectors at a regulated pressure. Unused fuel is returned to the fuel tank by a separate line.

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

1. Install fuel pressure gauge. Ignition "ON," pump pressure should be 284-325 kPa (41-47 psi). This pressure is controlled by spring pressure within the regulator assembly. Ignition may have to be cycled "ON" several times to obtain maximum pressure.

2. When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel regulator diaphragm. This will offset the spring and result in a lower fuel pressure. This idle pressure will vary somewhat depending on barometric pressure, however, the pressure idling should be less indicating pressure regulator control.

3. Pressure that continues to fall quickly is caused by one of the following:

^ In-tank fuel pump check valve not holding.
^ Fuel pressure regulator valve leaking.
^ Injectors sticking open.

4. An injector sticking open can best be determined by checking for a fouled or saturated spark plugs. If a leaking injector cannot be determined by a fouled or saturated spark plug, the following procedure should be used.

^ Remove fuel rail bolts, but leave fuel lines connected.
^ Lift fuel rail out just enough to leave injector nozzles in the ports.

CAUTION: Be sure injectors are not allowed to spray on engine and that injector retaining clips are intact. This should be carefully followed to prevent fuel spray on engine which would cause a fire hazard.

^ Pressurize the fuel system and observe for injectors leaking.