1. Engine exhaust is not smooth

 There are many methods to judge whether the three-way catalyst (hereinafter referred to as "TWC") is blocked and the muffler's internal sound insulation plate is welded, resulting in poor exhaust.

 The simplest method is to put your hand on the exhaust outlet of the liner, feel the exhaust capacity of the exhaust liner by hand. If the exhaust capacity is obviously less than that of other cars, it means that the engine is not smooth.

 Another method is to open the air filter and remove the filter element. If there is exhaust gas reflux during emergency acceleration, it means that the engine is not smooth.Detection of TWC blockage can also be seen in the color of the oxygen sensor contact.

 Tips:

 1 the color of the oxygen sensor contact is black, indicating that the mixture is too thick, and the front of TWC is blocked by coke.

 2 the color of the oxygen sensor contact is white, indicating that the cooling liquid enters the combustion chamber (the cooling liquid crystallizes into white), the oxygen sensor contact is polluted by the cooling liquid, and the front of TWC is blocked by the white crystallization of the cooling liquid.

 2. Comparison of the output voltage and waveform of the front and rear oxygen sensors

 Some engine TWC is equipped with oxygen sensors before and after. The front oxygen sensor is responsible for the open-closed-loop control of emissions, and the rear is responsible for monitoring TWC.In the road test, the decoder is used to read the data stream. Under normal circumstances, the output voltage of the front oxygen sensor changes rapidly between 0~1V (8 times/10s or more). Because TWC consumes the oxygen in the exhaust gas when it purifies the exhaust gas, the output voltage signal waveform of the oxygen sensor changes very slowly, which is close to a straight line of 0.5V, indicating that TWC works well.TWC has converted about 95% of the exhaust gas into harmless substances, and its outstanding performance is that the oxygen content is significantly reduced after TWC conversion.

 Hint:

 If the output voltage of the front and rear two oxygen sensors is exactly the same, it means that TWC has failed, lost the purification effect of the exhaust gas, and no longer consumes oxygen. Therefore, the amount of oxygen before and after TWC has no change, and TWC must be replaced.

 3. Use infrared thermometer to detect the temperature difference before and after TWC

 Under the normal working temperature of TWC in the normal driving of the car, the outlet temperature is at least 38 °C higher than the air inlet temperature, and the outlet temperature at idle speed should be 10 °C higher than the air inlet temperature.

 Hint:

 In the hot car state, lift the car, and use infrared thermometer to detect the temperature of TWC air inlet and outlet. If the temperature difference is less than 10 °C, it means that TWC is seriously blocked inside, and it must be replaced.

 4. The vacuum degree in the air inlet is too low at idle speed

 The vacuum degree in the air inlet at idle speed should be high. Pull any vacuum hose from the air inlet, seal it with your finger, and you should feel obvious vacuum suction;if the vacuum degree is too low, you can not feel obvious vacuum suction.

 Hint: If the engine idle stable, that means there is no leakage point in the intake system, because the intake system leakage, idle speed will drift to high idle speed, the greatest possibility is that the exhaust system is not smooth, TWC is more easily blocked by coke.

5. TWC blockage will cause exhaust gas reflux

 Open the upper cover of the air filter, press the accelerator pedal, and the exhaust gas will come out from the air filter.Under the working condition of the engine, the air flow inlet of the air filter can be detected by the exhaust gas analyzer, and HC can be detected. Therefore, if TWC is not replaced in time, it will cause the scaling of the hot wire or hot film of the air flow sensor, which will cause the fault of the mixture being too thin, and the exhaust gas can not be discharged in time.TWC blockage in addition to the speed can not go up, serious when the car can not start, usually the engine hot car idle speed is not as stable as the fast idle speed of the cold car, cold car idle speed is still OK, hot car idle speed is unstable, when accelerating, the exhaust gas returns from the air filter inlet, and the exhaust gas smell is choking.