| 摘要 |
PROBLEM TO BE SOLVED: To improve misfire diagnosis accuracy by surely preventing erroneous diagnosis caused by dispersion in combustion among cylinders, and dispersion in manufacture of projections or slits formed at a crank rotor for detecting a crank angle. SOLUTION: An engine speed at each specified crank angle in each cylinder is detected and a present cylinder #n in a combustion stroke is determined to specify the cylinder #n as a cylinder to be subjected to misfire diagnosis (S17). An engine speed MNXn is set with respect to the present cylinder #n in the combustion stroke (S18), a whole cylinder average rotational number MNXm is calculated based on the engine speeds MNSn,..., NMXn-4 in each of cylinders from the cylinder #n up to a cylinder before a specified combustion stroke (S19). Difference between the engine speed MXNn in the cylinder #n in the combustion stroke currently and the whole cylinder average rotational number MNXm is compared to a misfire determination level LVMIS (S20). When the difference exceeds the misfire determination level LVMIS, the cylinder #n to be subjected to misfire diagnosis is determined to be misfire (S21).
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