Fuel injector provided with a high flexibility plunger

A fuel injector (1) provided with an injection jet (3), an injection valve (7), which valve comprises a mobile plunger (15) to control the flow of fuel through the injection jet (3), and an actuator (6), which is capable of displacing the plunger (15) between a closed position and an open position of the injection valve (7); the plunger (15) comprises an elongate rod (29) mechanically connected to the actuator (6) and a sealing head (21) capable of engaging in sealing manner with a valve seat (16) of the injection valve (7); the rod (29) of the plunger (15) is of high flexibility and exhibits a flexibility parameter (P f ) of between 1 and 2 N/mm 2 .