Chart A7 - Fuel System Diagnosis: Notes

When the ignition switch is turned to the "ON" position, the ECM will turn on the in-tank electric fuel pump by energizing the fuel pump relay through circuit No. 465. The fuel pump will deliver fuel to the TBI unit, where the system pressure is controlled by the pressure regulator. Fuel pressure will be 9-13 psi (.6-.9 kg/cm² ) with the vacuum hose connected to the pressure regulator. Excess fuel is returned to the fuel tank via the fuel return line. A fuel pump test terminal is located on the left side of the engine compartment. When the engine is stopped, the pump can be turned on by applying battery voltage to the test terminal.

1. Test determines if the fuel pump will supply fuel pressure when energized through the fuel pump test terminal. If fuse in jumper wire blows, this indicates a short to ground in circuit No. 120. Use appropriate CHART A5 for determining applicable circuits and terminals.
2. Pressure less than 9 psi (.6 kg/cm² ) falls into 2 categories:
   • If regulated pressure is less than 9 psi (.6 kg/cm² ) and volume to injector is adequate, system will run lean and cause Code 44. Engine will be hard to start when cold and have poor overall performance.
   • A restricted fuel flow is causing pressure drop. Normally, a vehicle with fuel pressure of less than 9 psi (.6 kg/cm² ) at idle will not be driveable; however, if pressure drop occurs only when driving, the engine will surge then stop as pressure begins to drop.
3. When battery voltage is applied to the pump test terminal, and fuel line is gradually restricted, maximum fuel pump pressure of approximately 13-18 psi (.9-1.3 kg/cm² ) will develop.
4. This test determines if high fuel pump pressure is due to a restricted fuel line or a throttle body pressure regulator problem.