ARM 3D0409 - Caterpillar

General Operation of the Fuel System
Refer to Systems Operation, Testing, and Adjusting, "General Information" for locations of the components for the fuel system.
Illustration 1 g03059777
Typical example
(1) Fuel tank
(2) Primary fuel filter/water separator
(3) Fuel transfer pump
(4) Secondary fuel filter
(5) Fuel injection pump
(6) Fuel injectors
(7) Fuel return line from the fuel injection pump and the fuel injectors to the fuel tankWhen the engine is cranking, the fuel is pulled from the fuel tank (1) by the electric fuel transfer pump (3). A primary fuel filter/water separator (2) is installed between the fuel tank (1) and the fuel transfer pump (3). The primary fuel filter/water separator has an inline style filter. Refer to Operation and Maintenance Manual for more information on the service of the primary fuel filter/water separator. The fuel transfer pump forces the fuel through the secondary fuel filter (4) to the fuel injection pump (5).The secondary fuel filter (4) can also function as a water separator. The secondary fuel filter can be drained through a valve that is located at the bottom of the filter housing.The fuel injection pump sends fuel at high pressure to each fuel injector nozzle (6). The fuel injector nozzle sprays fuel into a precombustion chamber which slows the rate of combustion in the cylinder. The following items will result from reducing the rate of fuel combustion: prevention of engine knock, reduction of noise and reduction of emissions.
Illustration 2 g00468241
Phases of operation of the fuel injection nozzle
(A) Closed valve
(B) Open valve
(C) Fully open valveThe fuel injection nozzle injects fuel into the precombustion chamber at different angles during two phases. Most of the fuel is injected when the valve is fully open (C). This process is called indirect fuel injection. The results are more even combustion and complete combustion of the fuel at a reduced temperature. Improved fuel combustion will increase power output while reducing emissions and reducing fuel consumption.Excess fuel from the fuel injection nozzles and the fuel injection pump flows through fuel return line (7), through the injectors in the ARD and back to the fuel tank (1). The excess fuel aids the cooling of the fuel injection nozzles. Also, the fuel return line removes any air that is trapped in the fuel injection nozzles and the fuel injection pump.The fuel injection pump needs fuel for lubrication. If the precision parts of the pump are not adequately lubricated, the components may be easily damaged. The engine must not be started until the fuel injection pump is full of fuel that is free of air.The system must be primed by the electric fuel priming pump when any part of the system is drained of fuel. The following list contains examples of both service and repairs when you must prime the system:
The fuel filter is changed.
The low-pressure fuel line is removed.
The fuel injection pump is removed.
The fuel injection nozzles are removed.
The fuel tank is drained.
A leak exists in the low-pressure side of the fuel system.In order to release air from the fuel injection pump and the fuel