a unit fuel injector is disclosed to be used in a fuel injection system of an internal combustion engine wherein each unit injector is operated independently from one another and in synchronization with the internal combustion engine . specifically , the unit injector in accordance with the present invention includes a reciprocating plunger assembly within the unit injector that controls fuel metering as well as fuel injection , and a valve device positioned between a minor diameter plunger section and a cup of the unit injector so as to permit fuel flow in one direction for fuel injection and to restrict flow of gases in the opposite direction . the valve device effectively reduces carbon build - up on the injector surfaces and increases injector longevity while reducing maintenance . moreover , fuel metering is accurately controlled without substantial carboning flow losses .