Fuel injector with hydraulic coupling unit

The fuel injector has a hydraulic coupler unit, which has a cup-shaped coupler piston (51) and a valve piston, which is adjustably guided at a tube-shaped coupler body (52). The cup-shaped coupler piston and the tube-shaped coupler body are provided with an exterior peripheral surface (56) and an interior peripheral surface (57). The cup-shaped coupler piston is axially guided at the exterior peripheral surface of the coupler body, and the valve piston is axially guided at the interior peripheral surface of the coupler body.