| 摘要 |
PROBLEM TO BE SOLVED: To accurately perform diagnosis of leakages on the basis of a pressure change in an evaporated fuel system in tightly closed condition with a positive or negative pressure introduced, while opportunities for making diagnosis for even minor leakages are secured as much as possible. SOLUTION: Introduction of a positive or a negative pressure into an evaporated fuel system and subsequent closing are performed in a plurality of cycles, and pressure change in each closing is sensed so that pressure change values of a plurality of runs are obtained. The mean of the pressure changes is compared with the prescribed threshold for deciding, and leakage diagnosis is conducted. When the difference in the pressure change between the operating cycles is over a prescribed value, execution of the leak diagnosis is prohibited. Such a leakage diagnosis is conducted at off idling, and in idling, it is possible to perform leakage diagnosis on the basis only of the pressure change corresponding to one time, on the condition that the amount of evaporated fuel generated before establishing the tight closed condition be small. A large leakage diagnosis is conducted in the specified operating region, while it is arranged practicable to make minor leakage diagnosis in the prescribed operating region and at a steady run.
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