fuel injection apparatus for injecting gasoline or other combustible fuel into the cylinders of an internal combustion engine . the apparatus includes a fuel injector body having a diaphragm through which a needle valve extends and a constant fluid pressure is maintained on one side of the diaphragm to urge the needle valve toward closed position . a higher fluid pressure is intermittently applied to the other side of the diaphragm so that the needle valve is opened to spray fuel under pressure into the internal combustion engine , and when the higher pressure is relieved the introduction of fuel is interrupted .