The fuel system is composed by the fuel tank, the pump or the carburetor, the filter and the injectors and it is responsible for supplying fuel to the engine.

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Common rail is a diesel injection system that consists of a single pipeline, which connects the injection pump (a low pressure pump with a high pressure pump) to  a series of injectores electronically controlled, with autonomy between managing pressure and injection time. The pump doesn't determine how much fuel need to be injected, which is the job of the injectors.