Abstract: A fuel injection system (10) having a unique injector (226) cooperating with a unique pump (228) for blowing fuel into the combustion chamber (20) of a diesel engine (12). A reciprocating valve (202) and diaphragm (196) in the pump assembly (174) cooperate to periodically discharge vapor, such as compressed air or steam, and fuel to the injector (26). The vapor drives a piston assembly (32) and a valve assembly (36) to admit high-pressure vapor to a mixing chamber (124). Fuel is simultaneously supplied through a fuel valve assembly (130) to a fuel distribution ring (134) in the mixing chamber (124). The high-pressure vapor or gases blow the fuel from the mixing chamber (124) into the combustion chamber (20). Alternatively, the high-pressure vapor is replaced with a combustion product from a combustion chamber (257) formed in the injector (253). Combustion fuel is supplied through an intake valve (321) and excess gases are exhausted through exhaust valve (323).