a fuel injection system having a high pressure fuel injection pump whose high - pressure pumping is determined by an electrically controlled valve that controls a relief conduit , and the phase of the fuel injection is determined by the closure of this valve . to execute an injection that is subdivided into a preinjection and a main injection , and to simplify triggering of the electrically controlled valve , a cam that drives the pump piston is shaped such that the cam furnishes a range , in which the pump piston , to interrupt the injection between the preinjection and the main injection , remains in or moves back to its then - reached position .