Ignition performance monitor and monitoring method for capacitive discharge ignition systems

An ignition performance monitor for connecting between a capacitive discharge ignition system and a plurality of ignition coils each having a primary winding connected to receive ignition current pulses from said capacitive discharge ignition system and a second winding connected to fire a spark plug comprising

• a current sensing means connected to sense the current in each said primary winding and to provide a sense signal indicative thereof,
• a duration determining means connected to each said current sensing means and operative to provide an output signal for each time period during which the current sensed by the respective connected current sensing means exceeds zero amperes, said output signal having a pulse width which is indicative of the time period during which the current sensed by said current sensing means exceeds zero amperes, and processor means connected to receive the output signals form each said duration determining means, said processor means operating to store ignition coil data for each said ignition coil which includes a slope data value for each said ignition coil, the processor means operating to compute a firing voltage value indicative of the voltage required to fire each said spark plug using said output signal and ignition coil data for the ignition coil connected to fire said spark plug.

A method for monitoring the ignition performance of an internal combustion engine having ignition coils for firing engine spark plugs under the control of a capacitive discharge ignition system which includes

• determining the time period during which the current generated in the primary winding of an ignition coil by a pulse from the capacitive discharge ignition system takes to decay to a zero ampere level,
• and using the determined time period with a value indicative of the slope of the ignition coil to determine the firing voltage required to fire said spark plug.