An electronic ignition system for an internal combustion engine comprises an ignition coil (2) provided with at least a primary winding (3) and a secondary winding (4), a switch (6) connected to the primary winding (3) and drivable in an open and/or closed position according to the value of a driving signal, a control unit (7) associated to the switch (6) and configured to drive it in open and/or closed position according to the value of the driving signal (G). Such system also comprises a voltage changing electronic element (8) connected to the electrical connection (5), operatively interposed between the electrical connection (5) and the primary winding (3), and configured to change the voltage value of the primary winding (3) according to the value of a control signal between at least a first (V1) and a second (V2) voltage value. The system also comprises a ionization measuring device (20) around said discharge gap (100a) of the spark plug (100) associated with the secondary winding (4) and arranged to detect a current value in the secondary winding (4) and to send a signal representative of said value to the control unit (7), wherein the control unit (7) is configured to activate said measuring device (20) upon the shutdown of the electric arc or spark.