Leak diagnosis system for evaporative emission control system

摘要

A leak diagnosis system which diagnoses a leak condition of an evaporative emission control system for an internal combustion engine. The leak diagnosis system detects a changing speed of a pressure in the evaporative emission control system for plural times during when the evaporative emission control system is put into a negative pressure condition by the negative pressure of the engine and is then closed by a purge-cut valve. The leak diagnosis system diagnoses a leak condition of the evaporative emission control system according to the detected plural pressure changing speeds while taking a fuel condition in the evaporative emission control system into consideration on the basis of the detected plural pressure changing speeds. Accordingly, the leak condition in the evaporative emission control system is accurately diagnosed without being effected by the fuel condition.