• In the common rail system, an electronic control unit monitors various aspects of the engine (engine speed, throttle opening, coolant temperature, etc.) using information from sensors. In accordance with these data, the electronic control unit effects control over the fuel injection quantity, fuel injection timing, and fuel injection pressure in order to optimize the engine’s operation.
• The electronic control unit has a diagnosis function that enables it to recognize abnormalities in the common rail system’s major components and alert the driver to them.
• The common rail system consists mainly of an electronically controlled supply pump; injectors; a common rail; and the electronic control unit and sensors that are used to control the other components.

• When the engine is cranked by means of the starter switch, the feed pump (this is located inside the supply pump) simultaneously draws fuel from the fuel tank and feeds it via the fuel filter to the MPROP (rail pressure control valve). A quantity of fuel metered by the MPROP is supplied via the inlet valves to the plunger chambers.
• The fuel in the plunger chambers is pressurized. The outlet valves are then opened, and the fuel is fed under pressure to the common rail.
• The pressurized fuel is held in the common rail and then uniformly fed to the injectors.
• In response to signals from the engine electronic control unit, the injectors inject fuel into the relevant combustion chamber at the optimal timing and in the optimal quantity.




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