Fuel Pump (Applications Using Fuel Pump Relay For Fuel Pump ON/OFF Control)

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Fuel Pump (FP) is a PCM output signal that is used to control electric fuel pump. With PCM power relay contacts closed, Vehicle Power (VPWR) is sent to coil of fuel pump relay. For electric fuel pump operation, PCM grounds FP circuit, which is connected to coil of fuel pump relay. This energizes coil and closes contacts of relay, sending Battery Voltage (B+) through FP PWR circuit to electric fuel pump. When ignition switch is turned to ON position, electric fuel pump runs for about one second, but is then turned off by PCM if engine rotation is not detected. For applications with 2-speed fuel pumps, a normally closed low speed fuel pump relay is wired into fuel pump ground circuit. With low speed fuel pump relay contacts in normally closed position, there is no extra resistance in ground circuit, allowing high speed operation. For low speed fuel pump operation, PCM will ground Low Fuel Pump (LFP) circuit, which opens relay contacts, causing fuel pump ground circuit to pass through a resistor. See Fig 1. For additional fuel pump information, see FUEL DELIVERY under FUEL SYSTEM (GASOLINE).

Fig 1: Identifying 2-Speed Fuel Pump Circuits

Courtesy of FORD MOTOR CO.