Part 1 of 3

Chart A-7 (Part 1 Of 3):

Fuel Flow Diagram:

CIRCUIT DESCRIPTION:
When the ignition switch is turned "ON," the Electronic Control Module (ECM) will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving reference pulses. If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops.
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 injector. 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: Numbers below refer to circled numbers on the diagnostic chart.

1. Wrap a shop towel around the fuel pressure connector to absorb any small amount of fuel leakage that may occur when installing the gauge. Ignition "ON" engine "OFF," pump pressure should be 284-325 kPa (41-47 psi). This pressure is controlled by spring pressure within the regulator assembly.

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 is caused by one of the following:

^ In-tank fuel pump check valve not holding.
^ Fuel pressure regulator valve leaking.
^ Injector(s) sticking open.

4. An injector sticking open can best be determined by checking for a fouled or saturated spark plug(s). If a leaking injector can not be determined by a fouled or saturated spark plug the following procedure should be used.

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

WARNING: Be sure injector(s) 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 injector nozzles for leakage.