Td5 Technical - Electronic Unit Injectors

The electronic unit injector (EUI) is a special type of injector, developed and manufactured by Delphi for the Td5 engine. It utilises the ECM to provide precise injection of high-pressure fuel. This allows optimium efficiency and economy of the engine under all operating conditions.

Each EUI has its own five letter grading code (eg NCGGC). This code is used by the ECM to provide greater injection precision.

If the vehicle is fitted with a new ECM, the EUI grades for the fitted injectors must be entered into the new ECM using TestBook or equivalent.

When the engine is running, each injector is operated by an overhead camshaft. This operation draws fuel from the fuel supply drilling into the injector.

When the ECM determines that fuel injection is required, the ECM transmits an electrical pulse which energises the injector solenoid, closing the spill valve on the injector and locking fuel inside the body. As the cam begins to depress the injector, the fuel in the injector is pressurised to 1500 bar (1750 bar for the EU3 specification). When the fuel pressure exceeds the nozzle spring rate, the nozzle opens and injects fuel at very high pressure into the cylinder.

When the ECM determines that the injection period is over, the solenoid is de-energised, opening the spill valve and allowing fuel into the return circuit. The ECM controls the injection timing by altering the time at which the solenoid is energised and the injection period by controlling the period for which the solenoid is energised.

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