Electronic Unit Injector (EUI) Parts

Darwen Diesels stock a range of parts for Electronic Unit Injectors (EUI’s), but we also have a stock of the Injectors themselves. If we don’t have the EUI you particularly require, we are very happy to recondition any unit you have. If you send it to us, we aim to have it reconditioned within a day and back to you within 48 hours, depending on our volume of work and the availability of parts.

Core to the construction of an EUI is the plunger pump. This allows for low-pressure fuel delivery and return to all injectors, but at the same time provides extremely high- pressure atomisation and injection of diesel to a cylinder during an engine’s power cycle.

There are four phases in a EUI’s operation:

1. The fill phase is where there is a retraction of the plunger pump and diesel fuel is then drawn into the pump.
2. The spill phase is where the plunger pump starts to descend and the spill valve is open with diesel going back to the return line.
3. In the Injection phase the solenoid is activated, closing the spill valve. This occurs partway through the pump stroke; the diesel is forced through the nozzle creating a spray pattern in the cylinder.
4. Finally, in the pressure reduction phase, the spill valve is re-opened, almost at the end of the pump stroke, and diesel is allowed to recirculate again, ending the injection phase.

Electronic Unit Injectors, were designed mainly for use in commercial vehicles and large HGV’s, but they were used by Land Rover and Volkswagen for some passenger car diesel engines. EUI’s have been manufactured primarily by Bosch and Delphi, and we have appropriate parts for those EUI’s in stock.

Over time, and particularly since the advent of new tighter emissions standards, the use of Electronic Unit Injectors has declined and Common Rail has become the main system used for most diesel engines. It is also true to say that a small handful of manufacturers such as Scania and Volvo still use EUI’s for their trucks and heavy commercial vehicle.