The invention relates to a common rail fuel injector having an injector housing with a fuel inlet in communication with a central high-pressure fuel reservoir outside the injector housing and with a pressure chamber inside the injector housing. A control valve assures that a nozzle needle lifts from a seat when the pressure in the pressure chamber is greater than the pressure in a control chamber that communicates with the fuel inlet via an inlet throttle. The control chamber is defined by a bush that is displaceable, causing a sealing action, on the end of the nozzle needle remote from the combustion chamber and that is kept in contact against the injector housing with the aid of the nozzle spring.