Part 1 of 3

Chart A-7 - Fuel System Diagnosis (Part 1 Of 3):

Fuel System Components:

System Description:
When the ignition switch is turned "ON," the Powertrain Control Module (PCM) will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the PCM is receiving reference pulses. If there are no reference pulses, the PCM 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), supplies fuel through an in-line filter to the fuel passage within the lower manifold assembly. The pump is designed to provide sufficient fuel flow for all engine demands. 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.

The fuel pump "test" connector is located on the passenger side of the engine compartment near the relay center.

Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. Install fuel pressure gage. Refer to Part 3 of 3 and illustration. With ignition "ON" and fuel pump running, 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, manifold pressure is low (high vacuum) and is applied to the pressure regulator diaphragm. Vacuum will offset spring pressure and result in lower fuel pressure. Fuel pressure at idle will vary somewhat depending on barometric pressure, but should be less than pressure noted in Step (1).
3. A system that does not hold pressure is caused by one of the following:

^ Leaking fuel pump check ball.
^ Leaking fuel pump outlet seal.
^ Leaking valve/seat within pressure regulator.
^ Leaking injector(s).

4. An injector sticking open can best be determined by checking for a fouled or saturated spark plug(s).