Chart A-5 Fuel Pump Relay Circuit Diagnosis

Chart A-5 - Fuel Pump Relay Circuit Diagnosis:

Wiring Diagram For Chart A-5 - Fuel Pump Relay Circuit Diagnosis:

CHART A-5 - FUEL PUMP RELAY CIRCUIT DIAGNOSIS



Circuit Description:

When the ignition switch is turned "ON", the 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 distributor reference pulses. If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops. The pump will deliver fuel to the TBT unit where the system pressure is controlled to about 62 to 90 kPa (9 to 13 psi). Excess fuel is then returned to the fuel tank.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Turns "ON" the fuel pump if CKT 120 wiring is OK. If the pump runs, it maybe a fuel pump relay circuit problem, which the following steps will locate.

2. The next two steps check for power and ground circuits to the relay.



3. Determines if ECM can control the relay.

4. The oil pressure switch serves as a backup for the fuel pump relay to help prevent a no start situation. If the fuel pump relay was found to be inoperative, the oil pressure switch circuit should also be tested to determine why it did not operate the fuel pump.