Method for determining the closing time of an electromagnetic fuel injector

Method for determining the closing time (t 3 ) of an electromagnetic fuel injector (4); the method contemplates the steps of: applying at a starting time (t 1 ) of the injection a positive voltage (v) to the coil (16) of the electromagnetic actuator (14) in order to circulate through the coil (16) an electric current (i) which causes the opening of an injection valve (15); applying at an ending time (t 2 ) of the injection a negative voltage (v) to the coil (16) in order to annul the electric current (i) flowing through the coil (16); detecting the trend over time of the voltage (v) across the coil (16) after the annulment of the electric current (i) flowing through the coil (16); identifying a perturbation (P) of the voltage (v) across the coil (16); and recognizing the closing time (t 3 ) of the injector (4) that coincides with the time (t 3 ) of the perturbation (P) of the voltage (v).