An accurate control of a solenoid-operated fuel injector in a Diesel or gasoline engine specifies that a pull-in voltage (Vpull-in) higher than the generally available battery voltage (Vbatt) is applied to the injector, and that the injection is ended as quickly as possible, in order that the fuel injection closely follows the solenoid current profile. When the initial pull-in voltage is lower than the expected nominal value, a deviation of the injected fuel quantity appears with respect to the nominal quantity. This inconvenience is overcome by monitoring the actual value of a selected parameter, such as the actual value of the initial pull-in voltage (Vpull-in), and the injection start time (te) and the solenoid energizing time (ET) are correspondingly modified.