DIAGNOSTIC DEVICE FOR EVAPORATIVE SYSTEM

PROBLEM TO BE SOLVED: To perform an always high accuracy diagnosis in a diagnostic device for an evaporative system, in which evaporative fuel is released to the intake system of an internal combustion engine under a predetermined operating condition, by correcting diagnostic results by abnormality detecting means on the basis of detected results of state detecting means for detecting the state of a gauge system comprising a gage valve and a gage pipe. SOLUTION: When an evaporative system 20 is diagnosed, a purge valve 4 is firstly closed, a bypass valve 15 is opened, and a drain valve 10 is closed, respectively by an ECU 12, and after that, the purge valve 4 is opened. Next, the purge valve 4 is closed and pressure in an evaporation passing pipe 21 is measured, and also pressure is measured again after a predetermined time, then a pressure change is calculated by these pressure. Next, as in the same manner, the pressure change of a gauge valve 17 in its opening and closing conditions is measured, and the cross sectional area of a gauge orifice 19 is calculated by using the pressure change of two pressure. After that, a leak area is found out from pressure in an evaporative system 20 and the cross sectional area of the gauge orifice 19, then it is judged as abnormality in the case that this leak area is in a predetermined value or more.