Patent ID: 6907871

Claim:
An ignition timing control system for a variable-cylinder internal combustion engine which is operated by switching an operation mode thereof between an all-cylinder operation mode in which all of a plurality of cylinders are operated, and a partial-cylinder operation mode in which part of the plurality of cylinders are deactivated, the ignition timing control system comprising: deceleration operation-determining means for determining whether or not the engine is operated under predetermined deceleration operating conditions; fuel cut-off means for cutting off fuel supply to the engine, when it is determined by said deceleration operation-determining means that the engine is operated under the predetermined deceleration operating conditions; fuel cut-off delay means for delaying a start of cut-off of the fuel supply by said fuel cut-off means for a predetermined time period after satisfaction of the predetermined deceleration operating conditions; ignition timing-correcting means for correcting ignition timing in a retarding direction, when the cut-off of fuel supply is being delayed by said fuel cut-off delay means; and correction amount-setting means for setting an amount of correction of the ignition timing by said ignition timing-correcting means, to a different value, depending on whether the engine is in the all-cylinder operation mode or in the partial-cylinder operation mode.