Abstract: An apparatus and method are provided for detecting knock in a spark ignition internal combustion engine. The engine comprises at least one cylinder with a spark plug, engine condition sensors for sensing engine speed, engine angle and engine noise, and an engine management system (EMS) that receives signals from the sensors to determine engine angle and engine noise. The EMS has a nonvolatile memory, a spark plug driver, and a processor. The processor is arranged to control the spark driver to generate an ignition spark at a desired spark angle according to signals from at least some of the sensors, and determine over a first range of engine angles a background engine noise, and over a second range of engine angles an engine knock noise. The processor then retards (or advances) the spark angle if the level of knock noise relative to background noise exceeds (or falls below) a predetermined level.