Fuel System Diagnosis - High Pressure Side
FUEL SYSTEM DIAGNOSIS - HIGH PRESSURE SIDE
SUPPLY SYSTEM
The fuel flows through a pre-filter screen in the tank and to the engine through the fuel supply lines. There is no lift pump in the fuel tanks or on the frame. The fuel passes through the base plate of the fuel injector control module (FICM) to cool the module. From the FICM the fuel flows to the fuel filter assembly, which combines a water separator, a hand prime pump and a filter element. Within the assembly, there is also a fuel heater. The integrated hand pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The fuel injection pump at the front of the engine valley includes a fuel supply pump and a high-pressure pump. Fuel is drawn to the supply pump from the primary fuel tank by the supply pump and delivered to the high-pressure pump.
HIGH PRESSURE SYSTEM
The much larger section of the fuel injection pump assembly is the high-pressure pump. The pump is engine-driven by the camshaft gear. From the high-pressure pump, the fuel flows to the 2 common fuel rails. Each common fuel rail supplies one bank of 4 fuel injectors.
RETURN SYSTEM
The fuel return system routes fuel from the fuel injectors, the pressure relief valve, and the fuel injection pump. The return fuel travels to the fuel cooler and then to the fuel tank. This fuel is used to cool and lubricate the injection pump and the injectors.
DIAGNOSTIC AIDS
- The fuel return volumes vary based on the American Petroleum Institute (API) rating of the diesel fuel.
- A fuel injector may have high fuel return flow only at higher engine temperatures.
TEST
Steps 1-4:
Steps 5-9:
