MISFIRE DETECTING METHOD

PROBLEM TO BE SOLVED: To improve the sureness of misfire detection by forming corrective values for each cylinder from rough-running characteristic values characteristic of each cylinder during misfire-free operation so that the characteristic values characteristic of each cylinder coupled to the corrective values become equal with respect to each other. SOLUTION: On the basis of the segment times of each cylinder synchronized with ignition (S5.1), an unstable-running characteristic value Lut characteristic to the cylinder is computed (S5.2). A correction value for compensating torsional vibration and similar influence to equalize the unstable-running characteristic value is read from a load/speed characteristic data memory K (L, n) and coupled to the unstable-running characteristic value Lut (S5.4). A threshold Lur is read from a characteristic data memory Lur (n, L) (S5.5). If the corrected unstable- running characteristic value is judged to exceed the threshold Lur (S5.6), it is judged as the misfire of an internal combustion engine (S5.7), and an error signal is sent out to switch on an error lamp, for instance (S5.8).