Patent US 4,245,591

It is discriminated in an ignition timing control system for an internal combustion engine whether the ignition timing arithmetically calculated on the basis of sensed operating conditions of the engine lies within a predetermined range of ignition timing. When the result of discrimination indicates that the calculated ignition timing lies within the predetermined range, ignition occurs at that instant, while when the result of discrimination indicates that the calculated ignition timing does not lie within the predetermined range, the result of calculation is disregarded, and ignition occurs at a predetermined instant.