Powertrain Control Module - PCM

A-5 Chart:

A-5 Circuit:

Circuit Description:
When the ignition switch is turned "ON," the control module will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the PCM is receiving distributor reference pulses. If there are no reference pulses, the PCM will shut "OFF" the fuel pump within 2 seconds after ignition "ON" or engine stops.
On 4.3L, 5.0L and 5.7L applications 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.
On 7.4L applications the pump will deliver system pressure that is controlled to about 179-220 kPa (26 to 32 psi). Excess fuel is then returned to the fuel tank.

Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This procedure applies direct voltage to run the fuel pump. If the pump runs, it may be a fuel pump relay circuit problem which the following step will locate.

2. This step checks voltage from the battery and the ground circuit to the relay.

3. This test determines if there is voltage from the PCM terminal, "F6" to the relay connector.

4. This step completes the fuel pump relay circuit but if this diagnosis was used because the engine would not run then the oil pressure switch should also be diagnosed.


Diagnostic Aids: The PCM has integrated circuits that are fault protected, therefore, if a circuit has failed, the integrated circuits may not be damaged and will keep the circuit open until the fault has been corrected. When the fault has been corrected, reinstall PCM and check circuit. Replace PCM only if the circuit is still inoperative.