An ignition and engine control system for an internal combustion engine. The system includes a flyback ignition transformer which can rapidly re-fired a spark plug during a combustion cycle to perform various ignition diagnostic procedures using the spark plug as a feedback element of the control system. The transformer is adapted for mounting directly to a spark plug and includes a core about which a primary and secondary are toroidally wound. A controller provides signals to a circuit which causes maximum charging of the transformer for ignition and subsequent charging of the transformer for diagnostic purposes. The system also includes a diagnostic circuit which can detect the occurrence of an electrical discharge, and/or its duration, across the spark plug as a result of one of the diagnostic charges by monitoring the transformer for a reflected voltage in its primary. The detection circuit outputs a signal to the controller which allows the controller to diagnose conditions within the combustion cylinder.