A Mercedes Benz E260 limousine with a mileage of about 36 thousand km. The owner reflects the engine fault light and jitter is serious. After receiving the car, it is confirmed that the engine has the phenomenon of fire. After taking the car: the connection diagnostic instrument XENTRY for rapid detection, found that the ME (engine control module) has the current fault: P0302 00, the engine 2 cylinder has a continuous fire loss. Enter the data flow to see the number of engine misfires, the data is 0. The initial conjecture is the software malfunction of ME. Connect the diagnostic device to the server for online software upgrade. After the upgrade, the fault remained. Only the number of fires in the 2 cylinder of the data stream had reached 352 times. Further check the 2 cylinder ignition coil and spark plug. It is found that the head of the spark plug of the 2 cylinder has been completely damaged. The author preliminarily diagnosed the problem of spark plug. Replace the spark plug and check the car again. It is still found that the 2 cylinder is on fire. It seems that the cause of the fire is not as simple as it thought before. So we went to the next stage of inspection: changing the ignition coil of other cylinders, the trouble is still. The diagnostic instrument detects the data value and checks the high pressure fuel system oil pressure of the engine, normal. The oscillograph is used to detect the injector of the 2 cylinder, and the waveform is normal. The cylinder pressure gauge is used to check the tightness of the 2 cylinder, and the cylinder pressure value is 0. All the focus fell on the cylinder at this time. Is it suspected that the previous part of the spark plug was dropped into the cylinder causing the cylinder block to pull? But the pressure of the cylinder should not be 0. What is the reason why the pressure of the cylinder does not exist? In order to solve this mystery, an engine endoscope was used to inspect the cylinder block of the engine, but no obvious damage was found on the cylinder wall. Specifically, what causes the cylinder pressure to be completely absent, and where is the damage part of the spark plug? So the endoscope was used again to examine the intake and exhaust valves of the 2 cylinder, and finally confirmed that there was a big hole in the exhaust valve. After obtaining the consent of the technical department and the owner, the cylinder head inspection was disassembled and all the above judgments were confirmed. The cause of the engine 2 cylinder fire was that the spark plug head damage resulted in the damage of the exhaust valve, resulting in the failure of the cylinder pressure to work. It seems that the trouble is very simple, but we can think more about it. Why is there no obvious damage to the cylinder block of the engine? After that, the cylinder block is certified intact by the Ministry of technology. Why is the only exhaust valve damaged? Where did the damage part of the spark plug and exhaust valve go? Only the exhaust valve is damaged and the cylinder body is not damaged. The author judged that the spark plug head was damaged to the top of the piston when the 2 cylinder was ignited, and the exhaust door was ejected at the moment of work, and the falling debris entered the exhaust system. Can the exhaust system be discharged directly? Only three yuan catalytic converter is breakdown can be directly discharged to the outside world. In order to find out, remove the exhaust pipe with endoscopy, the three way catalyst is in good condition. So, where did the falling pieces go? Is it left in the turbocharger? So the turbocharger should have a different noise. The falling pieces were burned in the combustor? This is not possible. If the falling pieces can be burned, then other spark plugs and valves should also be burned. After repeated verification, it was concluded that the falling pieces were burned inside the exhaust pipe and discharged back to the outside world. The reasons are as follows: first, the temperature of the combustion chamber of the engine can not reach the level of burning because of the existence of cooling system. Secondly, if the falling debris is left in the combustion chamber, then the cylinder wall can not be avoided in the repeated work of the piston. Only the falling debris is left between the turbocharger and the three way catalytic converter. Under the high load condition of the engine, the exhaust pipe is red enough to burn the temperature and the particulate matter is discharged to the outside world.