An internal combustion engine having a fuel injector which functions as a positive displacement pump and dispenses an amount of fuel which is fixed for each and every operation of the injector, and a controller which controls the operation of the fuel injector. In response to an increasing engine speed and/or load the controller increases in amount the fuel delivered per engine cycle by increasing in number the occasions the fuel injector is operated per engine cycle. In response to a decreasing engine speed and/or load the controller reduces in amount the fuel delivered per engine cycle by reducing in number the occasions the fuel injector is operated per engine cycle.