Part 1 of 4

Chert A-7, Fuel System Pressure Test (1 Of 4):

Fuel Delivery Schematic (Tools Shown Installed For Testing):

CIRCUIT DESCRIPTION:

An electric fuel pump, attached to the fuel lever 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 which is an integral part of the fuel rail assembly, keeps fuel available to the injectors at a regulated pressure.

The fuel pump test terminal is located in the engine compartment. When the engine is stopped, the pump can be turned "ON" by applying voltage to the test terminal.

Improper fuel system pressure may contribute to one or all of these symptoms:

^ Codes 44 or 45.

^ "Cranks But Won't Run" condition.

^ Cuts out may feel like ignition problem

^ Hesitation, loss of power, or poor fuel economy.


TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. Install pressure gage J-34730-1 or equivalent to fuel pressure tap. Wrap a shop towel around the fuel pressure tap to absorb any leakage of fuel that may occur when installing fuel pressure gauge. With ignition "ON," pump pressure should be 284-325 kPa (41-47 psi). This pressure is controlled by spring pressure and throttle body vacuum within the pressure regulator assembly. 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 pressure and reduce fuel pressure by 21-69 kPa (3-10 psi).

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 (3-10 psi).

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.