1 A21PQXT-QXSQ SILENCER - FR 2 A21-1201210 SILENCER - RR 3 A21-1200017 BLOCK 4 A21-1200019 BLOCK 5 A21-1200018 HANGER II 6 A21-1200033 SEAL RING 7 A21-1200031 SPRING 8 A21-1200032 BOLT 9 A21-1200035 STEEL WHEEL ASSY 10 Q1840855 BOLT M8X55 11 Q1840840 BOLT - HEXAGON FLANGE 12 A21PQXT-SYCHQ THREE-WAY CATALYTIC CONVERTER 13 A21-1200034 STEEL WHEEL ASSY 14 A21FDJFJ-YCGQ SENSOR - OXYGEN 15 A11-1205313FA WASHER - THREE-WAY CATALYTIC CONVERTER 16 A21-1203110 PIPE ASSY - FRONT 17 B11-1205313 GASKET What are the components of the engine exhaust system Collect the exhaust gas in each cylinder of the engine, reduce the exhaust noise, eliminate the flame and spark in the exhaust gas, and purify the harmful substances in the exhaust gas, so that the exhaust gas can be safely discharged into the atmosphere. At the same time, it can also prevent water from entering the engine and protect the engine. [component composition of engine exhaust system]: exhaust manifold, three-way catalytic converter, oxygen sensor and muffler [functions of various components of engine exhaust system]: 
 1. Exhaust manifold: It is connected with the engine cylinder block to concentrate the exhaust gas in each cylinder to the exhaust manifold. 2. Three way catalytic converter: The harmful gases such as HC, CO and NOx (nitrogen oxides) in automobile exhaust are transformed into harmless carbon dioxide, water and nitrogen through oxidation and reduction. 3. Oxygen sensor: The air-fuel ratio signal of the mixture is obtained by detecting the content of oxygen ions in the exhaust, which is converted into an electrical signal and input into ECU. According to this signal, ECU corrects the injection time to realize the air-fuel ratio feedback control, so that the engine can get the best concentration of mixture, so as to reduce harmful gas emissions and improve fuel economy. (there are generally two, one behind the exhaust manifold and one behind the three-way catalyst. Its main function is to check whether the three-way catalyst can work normally.) 4. Silencer: Reduce exhaust noise. A silencer is installed at the outlet of the exhaust pipe to make the exhaust gas enter the atmosphere after silencing. Generally, 2 ~ 3 silencers are adopted. (the front muffler is [resistive muffler], which is used to absorb high-frequency noise; the rear muffler (main muffler) is [resistant muffler], which is used to reduce low-frequency noise.