A device for controlling an electronic engine ignition system (2) comprising a coil (3), the primary winding (4) of which is connected between a reference voltage and ground via a switch block (5), and the secondary winding (6) of which is connected between the electrode of a spark plug (7) and ground. The device comprises means for detecting, for the spark of each operating cycle, signals relative to the energy at the spark plug; means for computing engine speed; means for comparing the energy of the plug with optimum values for each engine speed; and means for controlling charging of the primary winding via a signal resulting from the above comparison, and for driving the switch block, so as to control energy supply to the plug for the spark of the next cycle. Further, the detected spark signals are used to diagnose the ignition system and an user is informed by indicating means of a fault condition.