An injector for a diesel engine is provided which includes a housing having an internal bore, and a reciprocating plunger disposed within the bore and coacting therewith to pump fuel, dampen plunger movement, and quickly vent fuel pressure to provide a sharp end of injection. The bore is generally coextensive with the housing and a spray tip is attached to the end of the bore to introduce fuel into a combustion chamber. The plunger forms a chamber at the end of the bore that expands to admit fuel and contracts to express fuel as the plunger reciprocates within the bore. The chamber has an upper portion that pumps fuel and a lower sealable portion that entraps fuel to dampen plunger movement. The plunger and bore also form a reciprocating spill valve above the chamber to vent fuel pressure. An internal inlet passage supplies fuel to the pumping chamber portion. An internal spray passage connects the pumping chamber portion to the spray tip. The spill valve communicates with the chamber. An internal relief passage connects the spill valve to an exit port.