A fuel injector includes fixed metal components, in particular an injector body, a solenoid actuator equipped with a retaining spring that holds a control valve stem, a control valve body including a seat for the control valve stem, a spacer between the body of the control valve and an injection nozzle, a control chamber, and an injection needle seat. The fuel injector also includes movable metal components, in particular the control valve stem and an armature thereof and an injection needle. Surfaces of the metal components that are in contact with one another are contact surfaces. Resistive surface coatings are arranged on a number of the contact surfaces. The overall electrical resistivity of the injector between the body of the solenoid actuator and the body of the injector varies by at least three distinct ohm values intermittently according to the kinetics of the injection needle of the injector.