Fuel System (Cab Chassis)

FUEL PUMP




The fuel pump is mounted in the fuel sender assembly. The fuel pump is an electric high pressure pump. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injectors. Excess fuel from the fuel rail assembly returns to the fuel tanks through the fuel return pipe. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions. The powertrain control module (PCM) controls the electric fuel pump operation through a fuel pump relay. The fuel pump flex pipe acts to dampen the fuel pulses and noise generated by the fuel pump.

SECONDARY FUEL PUMP - DUAL TANKS

The secondary fuel pump is a low pressure electric transfer pump. The secondary fuel pump is mounted outside the fuel tank on the left side of the body crossmember. The secondary fuel pump transfers fuel from the secondary fuel tank to the primary fuel tank when commanded by the powertrain control module (PCM). The PCM grounds the secondary fuel pump relay control circuit. Fuel level is continuously monitored in both tanks by the PCM. When the fuel level in the primary tank is approximately 2 gallons lower than that in the secondary tank, the secondary fuel pump is energized and approximately 4 gallons of fuel is transferred to the primary tank. The above actions continue until the primary tank fuel level is low enough that it will accept all of the remaining fuel in the secondary tank, at which time the secondary fuel pump is energized until the secondary tank is empty.