preignition is different than spark knock or knock. preignition is caused by something other than the spark igniting the mixture. usually it is just a hot metal area that causes the high compression mixture to ignite. basically the compression just gets too high and the mixture autoignites before the spark fires. preignition is unrelated to spark timing. spark knock, or just knock, is when the plug fires and the compressed mixture explodes all at once instead of a smooth slow burn like it should be. both preignition and spark knock are called detonation by many people but some people only equate detonation to preigition and not spark knock. both problems are related to compression that is too high. with and advanced timing, the plug fires too far BTDC which leads to the mixture actually burning at max compression which is TDC. instead of the smooth burn the high compression leads to an explosion and you hear a ping or knock. preignition is a problem you run into with a lean mixture or compression ratio or effective compression ratio on forced induction engines that is too high for the octane rating of the fuel. knock happens with timing advanced too far for the octane rating of the fuel.

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dew
86' 190e 2.3L 16v