Since the air-fuel ratio of the mixture deviates from the theoretical air-fuel ratio, the purification ability of the three-way catalyst for CO, HC and NOx will drop sharply. Therefore, an oxygen sensor is installed in the exhaust pipe to detect the concentration of oxygen in the exhaust gas, and The ECU sends a feedback signal, and then the ECU controls the increase and decrease of the fuel injection amount of the injector to control the air-fuel ratio of the mixture to be near the theoretical value.
