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Method of Controlling Common Rail Fuel Injection Device

Common Rail System Overview

4/21/2017 2:24 PM  | Author: Cindy

The key components within the common rail system are labelled in the diagram above and are as follows:

Electric feed pump (not present on all systems) – supplies fuel to the high pressure pump
Filter – it is vital that this is replaced in line with manufacturers recommendations to ensure system cleanliness and lifespan
Overflow valve – enables excess fuel to overflow back into the fuel tank
Return manifold – controls the return of fuel back to the fuel tank
High Pressure pump – the high pressure pump is the heart of the fuel system. This is where diesel fuel has it’s pressure increased – it is engine driven, system dependent and can generate in excess of 2,000 BAR – to put this pressure into perspective a common car tyre pressure would be around 2.5 to 3.5 BAR!

This pressure is usually controlled by one of 2 methods:

Regulating the quantity of fuel drawn into the high pressure pump, limiting the amount of pressure that can be generated.
Regulation of the generated pressure within the pump by releasing some of the pressure into the return lines back to the fuel tank.

In either case, the regulation of the pressure is controlled by the Electronic Control Module (ECM) after taking into account various input signals from sensors around the system and driver demands. Unlike mechanical systems these high pressure type pumps do not need to be timed with the engine as the injections timing is controlled by the ECM firing the injectors, and the pressure control valve is controlled by the ECU and varies rail pressure according to load demand.

The tolerances, environment in which the pumps are built, and the quality of components used when remanufacturing these pumps is critical to the correct operation of the vehicle and lifespan of the pump and system – if the pump internals fail or breakdown this can result in the need for a full fuel system replacement. The tolerances are smaller than the naked human eye can see!


High pressure control valve (not present on all systems) – controls pressure generated within the pump electronically (ECM Controlled)
Rail pressure sensor – monitors system pressure
Rail – this is the ‘common rail’ where fuel is stored and passed into the injectors for injection
Injectors – the injectors in the common rail system are controlled and operated by the ECM after taking into consideration multiple sensor and signal inputs. The manufacturing tolerances and components remain the same as the high pressure pumps and are critical to the operation and lifespan of the injector.

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