| 摘要 |
PROBLEM TO BE SOLVED: To solve problems that a known evaporation system diagnosis device diagnoses leakage of an evaporation system from a first pressure change when a passage from a fuel tank to an intake pipe is sealed, a second pressure change when a purge valve is opened, and evaporated gas is purged in the intake pipe of an internal combustion engine, and a third pressure change when the purge valve is finally closed, the third pressure change is fluctuated by the effect of the evaporated gas, and the threshold to determine presence/absence of small amount of leakage is hardly set, and the diagnosis accuracy is degraded because the difference between the third pressure change with small amount of leakage and the third pressure change without leakage is decreased under an operational condition of much generation of evaporated gas. SOLUTION: The difference between the third pressure change with small amount of leakage and the third pressure change without leakage is measured irrespective of generation of evaporated gas by changing the target pressure in a fuel tank according to the operational condition when measuring the second pressure change. COPYRIGHT: (C)2004,JPO
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