Ignition timing control method

An ignition timing control method for an internal combustion engine having at least one cylinder and a crankshaft, comprising the steps of:

• detecting a parameter which affects the ignition timing of the operating engine;
• generating at least one electrical signal which indicates the value of the detected parameter;
• and
• calculating, in response to said generated electrical signal, a spark advance angle which represents an optimum ignition timing at the value of said detected parameter, wherein the improvement comprises:
• selecting one reference crank angle position from a plurality of different reference crank angle positions for each cylinder, said selected reference crank angle position depending on the value of said calculated spark advance angle;
• calculating the difference angle between said selected reference crank angle position and the crank angle position corresponding to the calculated spark advance angle;
• sensing when the crankshaft rotates through the selected reference crank angle position;
• calculating an ignition control value which represents a period of time required by the crankshaft to rotate through said calculated difference angle;
• and
• producing an ignition spark in response to said ignition control value when said period of time has elapsed after the crankshaft rotates past said sensed selected reference crank angle position.