Abstract: An apparatus diagnoses and controls combustion of an internal combustion engine which makes smooth operation of an engine possible by adjusting the combustion condition at the occurrence of knock, misfire, and flame quenching and also makes it possible to detect the occurrence of abnormality in cylinder pressure detectors without delay and deal with the abnormality without stopping the operation of the engine. A maximum pressure ratio Pp/P0 is calculated, Pp being the maximum cylinder pressure and P0 being the compression pressure at one or a plurality of crank angles in the compression stroke Pp/P0 is compared with pressure ratios for each diagnosis category, the combustion conditions are diagnosed by judging the result of the comparison every cycle or plural cycles.

Abstract: An apparatus for diagnosing and controlling combustion of an internal combustion engine is provided which makes smooth operation of an engine possible by adjusting the combustion condition at the occurrence of knock, misfire, and flame quenching and also makes it possible to detect the occurrence of abnormality in cylinder pressure detectors without delay and deal with the abnormality without stopping the operation of the engine. The apparatus comprises a means to calculate the maximum pressure ratio Pp/P0, Pp being the maximum cylinder pressure, P0 being the compression pressure at one or a plurality of crank angles in the compression stroke, a means to compare said Pp/P0 with pressure ratios (threshold pressure ratios) predetermined for each of diagnosis categories, and a means(step) to diagnose the combustion condition such as cylinder pressure by judging the result of said comparison every cycle or every plural cycle.