Evaporative fuel control system for internal combustion engines

摘要

An evaporative fuel control system for an internal combustion engine having a throttle valve arranged in the intake system. A canister adsorbs evaporative fuel generated in the fuel tank. A purging passage extends between the canister and the intake system, for purging evaporative fuel into the intake system at a location downstream of the throttle valve, and a purge control valve is arranged across the purging passage, for controlling the flow rate of evaporative fuel supplied to the intake system through the purging passage. When the engine is in a predetermined operating condition, the flow rate of evaporative fuel supplied to the engine is changed by controlling the purge control valve, then the degree of influence of the evaporative fuel on an air-fuel ratio of a mixture supplied to the engine is detected before and after the changing of the flow rate of the evaporative fuel, and an operating error of the purge control valve is determined based on the detected degree of influence.