An engine operation control system which controls ignition timing is disclosed. The system fires all ignition elements simultaneously, at least one of the ignition elements being fired effectively and all other ignition elements fired ineffectively in accordance with a first firing advance, and at least another of the ignition elements fired effectively and all other ignition elements ineffectively in accordance with a second firing advance, the first and second firing advances being determined independently of one another in order that the timing of the effective firing of each ignition element is optimized.