BOLT 6V5215 - Caterpillar

General Operation of the Fuel System
Illustration 1 g00950107
(1) Fuel injectors (2) Fuel injection pump (3) Fuel tank (4) Water separator (5) Fuel transfer pump (6) Fuel filterWhen the engine is cranking, the fuel is pulled from fuel tank (3) by fuel transfer pump (5). The fuel transfer pump forces the fuel through the fuel filter (6) to the fuel injection pump (2) .The water separator (4) is located downstream of the fuel tank (3). The water separator (4) will trap water that gets inside of the fuel system. The fuel filter (6) removes any contaminants from the fuel before the fuel reaches the fuel injection pump (2) .The fuel injection pump (2) sends fuel at high pressure to each fuel injection nozzle (1). The fuel injection 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 flows through the fuel return line to the fuel tank (3). 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 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.Refer to Systems Operation, Testing and Adjusting, "General Information" for locations of the components for the fuel system.The fuel transfer pump is equipped with a priming button. When the priming lever is moved back and forth, pressure is applied in the fuel system. This will remove any air out of the fuel system.In order to release air from the fuel injection pump and the fuel injection nozzles, the nuts for the fuel injection nozzles should be loosened. The priming lever is operated until fuel, that is free from air, flows from each connection