| 摘要 |
PROBLEM TO BE SOLVED: To improve diagnostic accuracy in each cylinder abnormal diagnosis performed on the basis of an estimated result which has been yielded by estimating an air-fuel ratio in each cylinder based on a value detected by an air-fuel-ratio sensor located in an interfluent portion of an exhaust gas of an engine. SOLUTION: It is judged whether an engine operating state is in a given specific operating region (an operating region where estimated accuracy in estimating each cylinder air-fuel ratio is high based on the value detected by the air-fuel-ratio sensor) or not. When the engine operating state is in the specific operating region, an air-fuel ratio of an ith cylinder # i is estimated based on the value detected by the air-fuel-ratio sensor and then an inter-cylinder differenceΔaf (# 1) that is a difference between the estimated air-fuel ratio AF (# 1) and a reference air-fuel ratio is calculated. When the inter-cylinder differenceΔaf (# 1) has exceeded a given judgment value F, at the time a given delay time has elapsed since the inter-cylinder differenceΔaf (# 1) had exceeded the given judgment vale F, a process for incrementing a count value of an abnormal counter T (# 1) is started. Then, when the count value of the abnormal counter T (# 1) has exceeded a given abnormal count value, it is judged that the air-fuel ratio of the ith cylinder # i is abnormal. COPYRIGHT: (C)2008,JPO&INPIT |
