Fuel Pump: Description and Operation

Fuel Pump:

EARLY MODEL VEHICLES
The fuel pump is a submersible pump with a permanent magnet electric motor. Fuel enters the pump inlet tube after passing through a sock style filter and is pushed through the pump by the motor to the outlet. Voltage to the pump is supplied through the Auto Shut Down (ASD) relay. The pump contains a single check valve on the output side which restricts fuel movement in either direction, maintaining fuel system pressure at 100 kPa (14.5 psi), when the pump is not operating, and fuel pressure must be released prior to servicing the fuel system.

LATE MODEL VEHICLES
The fuel pump used is a positive displacement, immersible pump with a permanent magnet electric motor. Fuel pump voltage is supplied through the Auto Shut Down (ASD) relay. Fuel is drawn into the pump through a filter mounted in the tank on the submerged end of the input tube, and pushed through the electric motor to the outlet. Fuel pressure is regulated by the throttle body mounted regulator at approximately 265 kPa (39 psi). The pump contains a pair of check valves. The first check valve relieves internal fuel pump pressure, and regulates maximum pump output, by bleeding off excess pump output pressure back into the fuel tank. The second check valve mounted near the pump outlet line restricts fuel movement in either direction when the pump is not operating. This check valve maintains fuel pressure at regulated pressure (approximately 265 kPa (39 psi), even when the engine is turned off, therefore fuel pressure must be released prior to servicing the fuel system.