Part 1 of 3

Chart A-7:

Fuel Line Diagram:

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 ignition reference pulses. If no ignition reference pulses exist, the ECM will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops. An electric fuel pump, attached to the fuel sender assembly (inside the fuel tank), pumps fuel through an in-line filter to the fuel passage within the lower manifold 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 lower manifold assembly, 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. Turn ignition "ON," pump pressure should be 284-325 kPa (41-47 psi). This pressure is controlled by spring pressure within the regulator assembly.

2. When 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.
^ Leaking fuel pump connecting hose.
^ 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.