Air-fuel ratio control system for internal combustion engines

摘要

An air-fuel ratio control system for an internal combustion engine controls the air-fuel ratio of a mixture supplied to the engine in response to an output from a first air-fuel ratio sensor arranged in an exhaust passage at a location upstream of a catalyst for purifying exhaust gases emitted from the engine. A control parameter for use in controlling an operation of the engine is changed when deterioration of the catalyst caused by sulfur poisoning is detected to desulfurize the catalyst.