As with the Unit injector system, pressure is built up by the engine camshaft.
As this generally lies beneath a truck engine, the cam pitch is transferred to the small piston in the UP unit via a roller tappet. The cam is shaped in such a way that the desired high pressure of the fuel is generated as quickly as possible in the so-called plunger chamber below the piston. An electronically-controlled, fast-switching solenoid valve determines both start and finish of injection. The triggering duration determines the amount of fuel injected.