Fuel Pump: Description and Operation

Fig. 1 Fuel Pump Module - Gas Engines w/26 Or 34 Gallon Tank (Typical):

Fig. 2 Fuel Pump Module - Gas Engines w/35 Gallon Tank (Typical):

Fig. 3 Fuel Pump Module Components - Gas Engines (Typical):

FUEL PUMP MODULE
The fuel pump module on all gas powered engines is installed in the top of the fuel tank. The fuel pump module (Fig. 1), (Fig. 2) or (Fig. 3) contains the following:
- A combination fuel filter/fuel pressure regulator
- Electric fuel pump
- Fuel pump reservoir
- A separate in-tank fuel filter (at bottom of module)
- Rollover valve (certain modules)
- Fuel gauge sending unit (fuel level sensor)
- Fuel supply line connection at filter/regulator
- A threaded locknut retaining pump module to fuel tank
- A gasket between tank flange and module
- Auxiliary non-pressurized fuel supply fitting (not all engines)

The fuel gauge sending unit (fuel level sensor), and pick-up filter (at bottom of module) may be serviced separately. If the electrical fuel pump requires service, the entire fuel pump module must be replaced. The fuel filter/fuel pressure regulator may be serviced separately. Refer to Fuel Filter/Fuel Pressure Regulator Removal/Installation for additional information.

Refer to Fuel Pump, Fuel Filter/Fuel Pressure Regulator and Fuel Gauge Sending Unit.

FUEL PUMP
The fuel pump is located inside of the fuel pump module. A 12 volt, permanent magnet, electric motor powers the fuel pump.

Voltage to operate the electric pump is supplied through the fuel pump relay.

Fuel is drawn in through a filter at the bottom of the module and pushed through the electric motor gear set to the pump outlet.

Check Valve Operation
The pump outlet contains a one-way check valve to prevent fuel flow back into the tank and to maintain fuel supply line pressure (engine warm) when pump is not operational. It is also used to keep the fuel supply line full of gasoline when pump is not operational. After the vehicle has cooled down, fuel pressure may drop to 0 psi (cold fluid contracts), but liquid gasoline will remain in fuel supply line between the check valve and fuel injectors. Fuel pressure that has dropped to 0 psi on a cooled down vehicle (engine OFF) is a normal condition. Refer to the Fuel Pressure Leak Down Test for more information.