Chart A-5A Fuel Pump Relay Circuit Diagnosis (Two Fuel Tanks)

Chart A-5A - Fuel Pump Relay Circuit Diagnosis (Two Fuel Tanks):

Chart A-5 - Fuel Pump Relay Circuit Diagnosis (Two Fuel Tanks):

CHART A-5A - FUEL PUMP RELAY CIRCUIT DIAGNOSIS (TWO FUEL TANKS)


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 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 except when a fuel module is used.

The pump will deliver fuel to the TBI 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.

A fuel module is used on all 7.4L, G van with 5.7L, and all other 5.7L over 8500 GVW engines to correct a hot restart (vapor lock) during a high ambient condition. It is designed to over-ride the ECM two second pump operation and will run the fuel pump for twenty seconds at initial ignition "ON".


Test Description:

A quick check can be made by listening for the selector valve operation when pressing fuel tank selector switch and the ignition "ON". Checking selector valve circuit - CHART A-5A:

1. Disconnect fuel pump connector.

2. Disconnect fuel tank selector valve and meter switch connector.

3. Apply 12 volts to the fuel pump test terminal at the fuel pump relay.

4. Connect a test light between terminals "E" and "D" on the selector valve connector and move selector switch from top to bottom position. Light should be "ON" in both positions.

^ If light is "OFF" in both positions, check for open in that circuit or faulty switch.
^ If light is "OFF in one position, check for open in that circuit or a faulty switch.


Diagnostic Aids:

^ An inoperative fuel module may be the cause of a hot stall/no start condition. Check for power and ground circuit to the fuel module and a complete circuit to the pump from terminal "A". If OK, and the pump does not run for the specified 20 seconds at initial ignition "ON", replace the Fuel Module.