A pressure-responsive spring-biased cutoff valve for an open nozzle unit fuel injector in an internal combustion engine is provided allowing for the selective operation of a given number of cylinders during an engine low load or idling speed condition for improved white smoke control. The fuel injector of the present invention includes an injector body having a central bore with a reciprocating injector plunger positioned therein to form an injection chamber. The injection chamber is supplied with fuel from a supply passage through a metering orifice with the fuel cutoff valve located in the supply passage upstream of and adjacent to the metering orifice and in close proximity to the injection chamber for a substantial reduction in the entry of combustion gases and other unwanted substances into the fuel supply.
