Internal combustion engine fuel injector, and relative method of classifying and selecting a series of injectors

The injector (7) has a nozzle (13) closed by a rod (17) which is movable by the fuel pressure in a control chamber (52) having a discharge conduit (59) closed by a plug (61) controlled by an electromagnet (36). The rod (17) is movable, from a closed position closing the nozzle (13), to effect a maximum travel, so that the amount of fuel injected following the maximum travel is greater than a maximum amount of fuel required by the power curve. To classify the injectors (7), a series of injectors (7) is prepared with corresponding rods (17) movable from the closed position to effect the maximum travel; and the amount of fuel injected by each injector (7), after two strokes of the respective rod (17) smaller than the maximum travel, is tested.