Part 2 of 2

Chart A-5 Part 2 Of 2:

Chart A-5 Wiring Diagram:

CIRCUIT DESCRIPTION:

When the ignition switch is turned "ON", the ECM will energize the fuel pump relay which turns "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving distributor reference pulses. If there are no reference pulses, the ECM will de-energize the fuel pump relay which will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops.


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



6. Checks for open in the fuel pump relay ground CKT 450.

7. Determines if the ECM is in control of the fuel pump relay through CKT 465, (terminal "5").

8. The fuel pump control circuit includes an engine oil pressure switch with a separate set of normally open contacts. The switch closes at about (4 lbs) 28 kPa of oil pressure and provides an ignition path feed to the fuel pump. If the relay fails the pump will run using the ignition feed supplied by the closed oil pressure switch.


9. This step checks the oil pressure switch to be sure it provides battery feed to the fuel pump should the pump relay fail. A failed pump relay will result in extended engine crank time because of the time required to build enough oil pressure to close the oil pressure switch and turn "ON" the fuel pump. There may be instances when the relay has failed but the engine will not crank fast enough to build enough oil pressure to close the switch. This or a faulty oil pressure switch can result in "Engine Cranks But Won't Run."