Fuel Pump: Description and Operation

PURPOSE
The fuel pump supplies fuel under pressure to the injection manifold assembly.

OPERATION
The fuel pump is activated by the control relay and fuel pump relay #2. Fuel enters the inlet port through the tank filter and flows inside the motor to the discharge port. The discharge port contains a check valve to maintain residual fuel pressure when the pump is shut off. If fuel flow to the injection manifold is obstructed, fuel pressure is bypassed to the inlet port by the pressure relief valve.

NOTE: Power to the fuel pump is controlled by the ECM through the MFI relay.

When the ignition switch is set to START:

Current flows from the ignition switch through the MFI relay coil to ground. This turns on the MFI RELAY switch and drive power is supplied from the battery through the MFI relay switch to the fuel pump.

While the engine is running:

The engine control module keeps the power transistor on and energizes the MFI relay coil so that drive power is supplied to the fuel pump.