FAILURE DIAGNOSTIC DEVICE FOR EVAPORATIVE EMISSION PURGING SYSTEM

摘要

PROBLEM TO BE SOLVED: To judge abnormality in a bypass passage or a switching means in relation to a failure diagnostic device for an evaporative emission purging system. SOLUTION: An evaporative emission purging system is provided with a canister 78 adsorbing evaporated fuel in a fuel tank 40, a bypass passage 88 bypassing the canister 78, and a bypass VSV 90 for controlling a leading state from the bypass passage to a purge passage. A venturi 88a is provided at the bypass passage 88 so that he ventilation resistance in the bypass passage 88 is larger than that in the canister 78 in ordinary state. The flow rate of gas flowing from an air chamber 46 toward an intake passage 50 is changed in response to the ventilation resistance of the passage. In this case, tank pressure PTNK in the air chamber 46 converge to a value which corresponds to the ventilation resistance in the passage between the air chamber 46 and the intake passage 50. Clogging abnormality in the bypass passage 88 and locking abnormality in the bypass VSV 90 are judged based on the tank pressures PTNK before and after a driving signal is supplied to the bypass VSV 90.