Method for recalibrating the injection law of a fuel injector

A method for refreshing the injection law of a fuel injector (4) to be tested in an injection system; the method includes the steps of: establishing the desired fuel quantity (Qd) for the fuel injector (4) to be tested; performing at least one first measurement opening of the fuel injector (4) to be tested in a test actuation time (T); determining a pressure drop (P) in a common rail (5) during the first measurement opening of the fuel injector (4) to be tested; determining a first fuel quantity (Q1) which is fed during the first measurement opening; calculating a second fuel quantity (Q2) as the difference between the desired fuel quantity (Qd) and the first fuel quantity (Q1); and performing a second completion opening of the fuel injector (4) to be tested for feeding the second fuel quantity (Q2) needed to reach the desired fuel quantity (Qd).