Part 1 of 3

Chart A-7 Part 1 Of 3:

Chart A-7 Diagram:

CIRCUIT DESCRIPTION:


An electric fuel pump, attached to the fuel level meter assembly (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, an integral part of the fuel rail 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 terminal is located in the engine compartment. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to the test terminal.

Improper fuel system pressure may contribute to:

^ Codes 44 or 45.
^ Cause a "Cranks But Won't Run" condition.
^ Hesitation, loss of power, poor fuel economy.
^ Cuts out, feels like an ignition problem.



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

1. Use pressure gage J 34730-1. Wrap a shop towel around the fuel pressure connector to absorb any small amount of fuel leakage that may occur when installing the gage. 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 and manifold vacuum. Pressure should not leak down after the fuel pump is shut "OFF".

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 approximately 21-69 kPa.

3. The application of 12-14 inches of vacuum to the pressure regulator should result in a fuel pressure drop of at least 21-69 kPa (3-1 psi).

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

^ In-tank fuel pump check valve not holding.

^ Pump coupling hose or pulsator leaking.

^ Fuel pressure regulator valve leaking.

^ Injector(s) sticking open.