Fuel Pump: Description and Operation

Fig. 9 Fuel Pump Module:

FUEL PUMP MODULE
The fuel pump module is installed in the top of the fuel tank Fig. 9. The fuel pump module contains the following:
- Electric fuel pump.
- Fuel pump reservoir
- Inlet strainer.
- Fuel pressure regulator.
- Fuel gauge sending unit
- Fuel supply and return line connections

The inlet strainer, fuel pressure regulator and level sensor are the only serviceable items. If the fuel pump requires service, replace the fuel pump module.

ELECTRIC FUEL PUMP
The electric fuel pump is located in and is part of the fuel pump module. It is a positive displacement, gerotor, immersible pump with a permanent magnet electric motor.

The fuel pump module is suspended in fuel in the fuel tank. The pump draws fuel through a strainer and pushes it through the motor to the outlet.

The pump contains two valves.
- One valve relieves internal fuel pump pressure and regulates maximum pump output.
- The second valve, in the pump outlet, maintains pump pressure during engine off conditions.

The fuel pump relay provides voltage to the fuel pump.

The fuel pump has a maximum deadhead pressure output of approximately 900 kPa (130 psi).

The regulator adjusts fuel system pressure to approximately 338 kPa (48 psi).

CIRCUIT OPERATION
The fuel pump motor, located in the fuel tank, is controlled by the fuel pump relay located in the Power Distribution Center (PDC). Power for the coil side of the relay is provided by circuit F12. The F12 circuit is HOT in the START and RUN position only and protected by a 10 Amp fuse located in cavity 10 of the PDC.

Circuit A21 is used to power the fuse and is connected between the ignition switch and the PDC. Power for the A21 circuit is provided by circuit A1. This circuit originates in the PDC and is protected by a 20 Amp fuse located in cavity 8.

The F12 circuit is spliced and provides voltage to the Powertrain Control Module (PCM) and the Controller Anti-Lock Brake (CAB) module.

The ground for the coil side of the relay is controlled by the PCM through circuit K31. The K31 circuit connects to cavity 74 of the PCM. Logic internal to the PCM determines when the coil side of the relay should be grounded.

When the PCM grounds circuit K31, the contacts in the fuel pump relay CLOSE connecting circuits A11 and A141. Circuit A1 is connected to the BUS bar in the PDC, HOT at all times, and protected by a 20 Amp fuse located in cavity 8. Circuit A141 is connected from the relay to the fuel pump motor. Ground for the fuel pump motor is provided on circuit Z1.