Fuel Pump Operation

After the low pressure fuel is filtered by the secondary fuel filter, it enters the high pressure fuel injection pump. When the fuel reaches the high pressure pump, a portion of the fuel flows to the lubrication valve allowing the fuel to lubricate the mechanical components of the high pressure injection fuel pump. Fuel that is not used for pump lubrication is directed to the fuel volume control valve. The fuel volume control valve regulates how much fuel enters the inlet one way check valve and the 2 main pump pistons. For additional information, refer to ENGINE CONTROL COMPONENTS , Fuel Volume Control Valve. The 2 main pump pistons are actuated by the main shaft offset journal. The offset journal of the main shaft uses a freespinning hub to make contact with the 2 main pump pistons. The pistons start their compression stroke when actuated by the offset journal and are returned to their rest position by the spring pressure. The fuel is drawn into the main cylinder while the piston returns to the rest position. The outlet check valve ball remains closed while the fuel is drawn in due to suction. Once the piston starts its compression stroke, the inlet oneway check valve closes using spring and fuel pressure and the outlet check valve opens due to increasing fuel pressure. After the high pressure fuel leaves the 2 main pump pistons, a portion of the fuel leaves the high pressure fuel injection pump and flows to the fuel cooler and the rest of the fuel is delivered to the high pressure fuel rails and fuel injectors. Fuel rail pressure is controlled at the rear of the left fuel rail by the fuel pressure control valve. The fuel pressure control valve adjusts the fuel pressure by restricting the fuel flow to the return line. For additional information, refer to ENGINE CONTROL COMPONENTS , Fuel Pressure Control Valve.

During certain driving conditions the PCM cycles the fuel pump on and off for testing purposes and is considered normal operation.