System for detecting deterioration of a three-way catalyst of an internal combustion engine

摘要

A system for detecting deterioration of a three-way catalyst of an internal combustion engine. Cutting-off of the fuel supply to the engine is started when the engine is decelerated with the throttle valve substantially fully closed, and the fuel supply to the engine is resumed when the rotational speed of the engine has become lower than a predetermined value. Time is measured which output from the air-fuel ratio sensor has required to reach a predetermined reference value after the resumption of the fuel supply to the engine. It is determined that the three-way catalyst is deteriorated when the time measured is shorter than a predetermined time period.