Emission Control Systems - Catalytic Converter

To minimize the amount of pollutants released into the atmosphere, a catalytic converter is installed in the exhaust system. The system has a feedback loop that includes an oxygen sensor (lean mixture sensor) in the exhaust gas. The sensor continuously supplies the electronic control unit with information on the exhaust gas composition, which allows the unit to correct the air-fuel mixture for better catalyst operation. The oxygen-sensitive exhaust gas sensor sends a signal to the control unit, the voltage of which depends on the amount of oxygen contained in the exhaust gas. If the air-fuel mixture entering the engine is too rich, the sensor sends a high-voltage signal to the unit. When the mixture becomes leaner, the signal voltage decreases. The best conversion of all toxic substances is achieved with a chemically correct air-fuel ratio, which ensures complete combustion of the fuel. This ratio is called the stoichiometric ratio and is 14.7 parts by weight of air to 1 part of fuel. The sensor has its highest sensitivity near this point, and the control unit responds precisely to changes in the mixture by changing the fuel injection time of the injectors. The sensor has a built-in heater to bring the sensor quickly to its operating temperature.

Do not use leaded gasoline containing tetraethyl lead in a vehicle with a catalytic converter. It will coat the inner surface of the catalyst containing precious metals, reduce its efficiency, and ultimately destroy the catalyst. Always keep the fuel and ignition systems in good condition. If engine misfiring is observed, do not drive the vehicle (or drive as little as possible) until the fault is corrected. Do NOT start the engine by towing or push-starting. This will allow unburned fuel to reach the active surface of the converter and overheat it when the engine starts. Do NOT turn off the ignition at high engine speed. Do NOT use unverified fuel or engine oil additives: they may contain substances harmful to the catalytic converter. Do NOT drive the vehicle if the engine requires frequent oil top-ups and blue smoke comes from the exhaust pipe. Remember that the catalytic converter operates at very high temperatures. Therefore, do NOT stop the vehicle after prolonged driving on dry grass, in tall grass, or over a pile of dry leaves.

Remember that the catalytic converter is FRAGILE. Do not strike it with tools during maintenance and repair.