Method for determining the closing time (t 3) of an electromagnetic fuel injector, which comprises a pin movable between a closed position and an open position of an injection valve and an electromagnetic actuator equipped with a coil and adapted to determine the displacement of the pin between the closed position and the open position; the method comprises the steps of: applying at a starting time (t 1) of the injection a positive voltage (v) to the coil of the electromagnetic actuator in order to circulate through the coil an electric current (i) which causes the opening of the injection valve; applying at an ending time (t 2) of the injection a negative voltage (v) to the coil of the electromagnetic actuator in order to annul the electric current (i) flowing through the coil; detecting the trend over time of the voltage (v) across the coil of the electromagnetic actuator after the annulment of the electric current (i) flowing through the coil and until the annulment of the voltage (v); identifying a perturbation of the voltage (v) across the coil after the annulment of the electric current (i) flowing through the coil by calculating the first derivative in time of the voltage (v) across the coil after the annulment of the electric current (i) flowing through the coil; and recognizing the closing time (t 3) of the injector that coincides with the time (t 3) of the perturbation of the voltage (v) across the coil after the annulment of the electric current (i) flowing through the coil; the method is characterized in that the step of identifying the perturbation of the voltage (v) across the coil comprises the further steps of: calculating an absolute value of the first derivative in time of the voltage (v) across the coil; calculating an integral over time of the absolute value of the first derivative in time of the voltage (v) across the coil; and identifying the perturbation when the absolute value of the integral over time of the first derivative in time of the voltage (v) across the coil exceeds a threshold value. applying at a starting time (t 1) of the injection a positive voltage (v) to the coil of the electromagnetic actuator in order to circulate through the coil an electric current (i) which causes the opening of the injection valve; applying at an ending time (t 2) of the injection a negative voltage (v) to the coil of the electromagnetic actuator in order to annul the electric current (i) flowing through the coil; detecting the trend over time of the voltage (v) across the coil of the electromagnetic actuator after the annulment of the electric current (i) flowing through the coil and until the annulment of the voltage (v); identifying a perturbation of the voltage (v) across the coil after the annulment of the electric current (i) flowing through the coil by calculating the first derivative in time of the voltage (v) across the coil after the annulment of the electric current (i) flowing through the coil; and recognizing the closing time (t 3) of the injector that coincides with the time (t 3) of the perturbation of the voltage (v) across the coil after the annulment of the electric current (i) flowing through the coil; the method is characterized in that the step of identifying the perturbation of the voltage (v) across the coil comprises the further steps of: calculating an absolute value of the first derivative in time of the voltage (v) across the coil; calculating an integral over time of the absolute value of the first derivative in time of the voltage (v) across the coil; and identifying the perturbation when the absolute value of the integral over time of the first derivative in time of the voltage (v) across the coil exceeds a threshold value. calculating an absolute value of the first derivative in time of the voltage (v) across the coil; calculating an integral over time of the absolute value of the first derivative in time of the voltage (v) across the coil; and identifying the perturbation when the absolute value of the integral over time of the first derivative in time of the voltage (v) across the coil exceeds a threshold value.