Abstract: An ignition system, of the type having ignition coils supplying energy to spark plugs in an internal combustion engine, includes apparatus to measure an electrical characteristic indicative of spark duration and generate a representative spark duration signal therefrom, or alternately to directly measure spark duration and generate a representative spark duration signal. Computational circuitry receives the spark duration signal and a spark duration setpoint signal, computes the error between the setpoint and the actual spark duration on a real-time basis, and modulates the energy in the high energy power supply to the ignition coils for maintaining a constant spark duration.

Abstract: The ignition performance monitoring method and apparatus determines the time period during which the current generated in the primary winding of an ignition coil by a pulse from a capacitive discharge ignition system takes the decay to a zero ampere level and uses this determined period to calculate and indicate the firing voltage required to fire a spark plug. The apparatus includes a current sensor connected to sense the current in the primary winding of the ignition coil and a comparator to compare the sensed current with a reference indicative of a zero ampere current level. The comparator provides an output signal having a pulse width indicative of the time the sensed current was above the zero ampere level to a processor which uses the output signal and data values unique to the ignition coil employed to determine a firing voltage for a spark plug fired by the ignition coil.