Chart A-5 Fuel Pump and Relay Electrical Test

Chart A-5 Fuel Pump Relay Circuit:

Fuel Pump Relay Circuit:

CIRCUIT DESCRIPTION:
When the ignition switch is turned "ON," the ECM will energize the fuel pump relay and run the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving ignition reference pulses. If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after the ignition is "ON" or engine stops. Should the fuel pump relay or the 12.0 volts used to drive the relay fail, the fuel pump will be controlled through the oil pressure switch back-up circuit. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to the test terminal. See LOCATIONS for fuel pump test connector.

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

1. At this point, the fuel pump relay is operating correctly. The back-up circuit through the oil pressure switch is now tested.

2. After the fuel pump relay is replaced, continue with the oil pressure switch test.

DIAGNOSTIC AIDS:
An inoperative fuel pump relay can result in extended cranking times. The extended crank period is caused by the time necessary for oil pressure to reach the pressure required to close the oil pressure switch and supply the necessary current for the fuel pump. Excess fuel may also cause long cranking times. This would usually be accompanied by a start that is not as fast as normal (once fired, the engine does not build up speed as fast) and a puff of black smoke at the tailpipe. An improperly connected or faulty EVAP canister control valve can cause this problem. Related Tests, Information and Procedures One or more leaking fuel injectors may also extend the cranking time. Chart C-2A Fuel Injector Balance Test