Method for determining the injection law of a fuel injector

A method for determining the injection law of a fuel injector (4) to be tested; the method includes the steps of: interrupting the feeding of fuel from the fuel pump (6) to the common rail (5); avoiding the opening of all the fuel injectors (4) except for the fuel injector (4) to be tested; measuring the initial fuel pressure (Pi) inside the common rail (5) before starting the opening of the fuel injector (4) to be tested; opening the fuel injector (4) to be tested for a number (N) of consecutive openings greater than one with a same test actuation time (T); measuring the final fuel pressure (Pf) inside the common rail (5) after ending the opening of the fuel injector (4) to be tested; and estimating as a function of a pressure drop (”P) in the common rail (5) the fuel quantity (Q) which is actually injected by the fuel injector (4) to be tested when it is opened for the test actuation time (T).