Fuel Pump: Description and Operation

Fuel Pump/Gauge Sending Unit:

The fuel pump is a gear/rotor type driven by a permanent magnet, 12 volt electric motor that is immersed in the fuel tank. The fuel pump module also contains the fuel gauge sending unit. The fuel pump utilizes a check valve at the outlet tube that consists of a check ball and spring. When the pump is not operating spring pressure holds the valve closed, preventing fuel from flowing back through the pump. When the pump is operating fuel pressure forces the ball off its seat allowing fuel to flow. Fuel system operating pressure is maintained at 214 kPa (31 psi) when the pump is operating and vacuum is supplied to the fuel pressure regulator. In the event of a loss of vacuum to the regulator system pressure will be about 55-69 kPa (8-10 psi) higher. When the fuel pump is not operating, vehicle is not running, a system pressure of 131-269 kPa (19-39 psi) is held by the fuel pump check valve and the fuel pressure regulator.