Actuator for a fuel injector of an internal combustion engine

has a gas exchange passage running through an adjustment drive housing (52, 54). There is a sealing unit (24) for the piezo-actuator (12) on the head unit (16, 18). This unit has a carrier (28) with sealing material (30) to seal the connection pins and a head unit. This includes an integrated micro-porous gas exchange part (26).