Patent ID: 7293453

Claim:
A misfire detection system for an internal combustion engine, comprising rotation detecting means for measuring a time required for a crankshaft of an internal combustion engine to rotate through a certain angle, and signal processing means for processing the time required for the rotation and detecting a misfire in said internal combustion engine, wherein said signal processing means comprises: a non-combustion state time-required-for-rotation memory for storing the time required for the rotation per cylinder when a fuel cut command is issued; a combustion variation memory in which a combustion variation per cylinder is stored in a stage of engine production; a filter for extracting a particular component from a value obtained by subtracting the sum of the time required for the rotation in a non-combustion state and the combustion variation, which are outputted respectively from said two memories, corresponding to a cylinder determined to be in the combustion stroke, from the time required for the rotation outputted from said rotation detecting means; and threshold determination means for determining the occurrence of a misfire when an output of said filter exceeds a threshold.