Misfires over multiple combustion cycles of the internal combustion engine are tested for, and abnormalities are evaluated on the basis of the results of said testing.

An adaptive method of detecting a misfiring cylinder in a spark-ignited internal combustion engine during substantially all engine operating conditions, including most no-load operation.

Method and system for detecting misfire in a reciprocating internal combustion engine having an engine cycle frequency in the frequency domain from crankshaft angular velocity.