Chart A-7 Fuel System Diagnosis: Notes

With ignition on, the ECM activates fuel pump relay which energizes the in-tank electric fuel pump. The fuel pump operates as long as ECM receives an ignition reference pulse. If there is no ignition reference pulse, fuel pump stops within 2 seconds. The fuel pump delivers fuel to the TBI unit where pressure is controlled at 9-13 psi. Excess fuel is returned to fuel tank. The fuel pump test terminal is located on the right side of engine compartment. When engine is stopped, fuel pump can be turned on by applying battery voltage to test terminal.

1. Fuel system has pressure, but less than 9 psi, falls into 2 areas:
   • Fuel volume okay but pressure too low. System will run lean and may set a Code 44. Hard starting and poor performance.
   • Check for restriction in fuel flow. Normally a vehicle with less than 9 psi fuel pressure at idle will not be driveable. However, if the pressure drop occurs only when driving, the engine will surge and then stop as pressure drops to zero.
2. Restricting the fuel return line allows the fuel pump to develop maximum pressure. When battery voltage is applied to fuel pump test terminal, pressure should be 13-18 psi.
3. This test determines if high fuel pressure is due to restricted fuel return line, or a TBI fuel pressure regulator problem.