An analog signal of a direct current potential magnitude proportional to the peak combustion pressure of a monitored internal combustion engine cylinder is simultaneously applied to two mutually exclusive comparator circuits, each being arranged to produce a separate respective output signal when the monitored cylinder peak combustion pressure is less than a first predetermined value or greater than a second higher predetermined value. With a signal present upon the output of either comparator circuit, upon the occurrence of a clock signal produced when another selected engine cylinder is later fired, either an ignition spark advance or an ignition spark retard signal is produced as determined by the comparator circuit output signal present. The adjustable ignition spark timing mechanism of an associated ignition distributor is operated to retard the ignition spark in response to an ignition spark retard signal and to advance the ignition spark in response to an ignition spark advance signal. A reset signal produced after the clock signal resets the circuit in preparation for the next firing of the monitored cylinder.