Chart A-5 Engine Cranks But Won't Start (Fuel System)

Fuel Pump Relay Circuit Test:

Fuel Pump Relay Wiring Diagram:

CIRCUIT DESCRIPTION:

When the ignition switch is turned "ON," the Electronic Control Module (ECM) will turn "ON" 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 key "ON". Should the fuel pump relay or the 12V relay drive from the ECM fail, the pump will be run through an oil pressure switch back-up circuit.


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

1. This test will determine if the oil pressure switch is closing and supplying voltage to the fuel pump when the relay is not functioning.

2. This test will determine if the oil pressure switch is stuck open


DIAGNOSTIC AIDS:

An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold or engine oil pressure is low. The extended crank period is caused by the time necessary for oil pressure to build enough to close the oil pressure switch and turn "ON" the fuel pump.