Part 1 of 2

Chart A-7 Part 1 Of 2:

Fuel System Diagram:

CIRCUIT DESCRIPTION:

The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled. Excess fuel pressure is bypassed back to the fuel tank. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to the test terminal located in the engine compartment.

Improper fuel system pressure may contribute to:

^ Codes 44 or 45.
^ A "Cranks But Won't Run" condition.

CAUTION: To reduce the risk of fire and personal injury, it is necessary to relieve the fuel system pressure before servicing fuel system components.

^ Disconnect negative battery terminal to avoid fuel discharge if an accidental attempt is made to start the engine.

^ Loosen the fuel filler cap to relieve fuel tank pressure.

^ Install pressure gauge J-34730-1 or equivalent to fuel pressure tap.

^ Install bleed hose into a approved container and open valve to relieve pressure. Fuel system is now safe for servicing.

^ Drain any fuel remaining into an approved container.

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS/ECM CONNECTOR IDENTIFICATION for correct color code identification of circuit.

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

1. Install pressure gauge J 34730-1 or equivalent to fuel pressure tap. Start engine. With ignition "ON" pump pressure is controlled by spring pressure and throttle body vacuum within the pressure regulator assembly. Turn ignition "OFF" for 10 seconds. Pressure should not leak down after the fuel pump is shut "OFF."

2. When the engine is idling, the throttle body vacuum is high and is applied to the fuel regulator diaphragm. This will offset the spring and result in a lower fuel pressure.

3. The application of 40-46 kPa (12-14" HG) of vacuum to the pressure regulator should result in a fuel pressure less than step 1.

4. Pressure that leaks down may be caused by the in-tank fuel pump check valve not holding, the pump coupling hose leaking, fuel pressure regulator valve leaking or an injector sticking open.