A Jianghuai Ruifeng 6500AIBE3 business car with a mileage of about 35 thousand km and a 4GJS gasoline engine equipped in 2007. The car has a slightly longer stopping time (usually one night) after normal driving. When the engine is started again, the engine sometimes has a few seconds of jitter, and then everything will be normal, and sometimes the engine fault lights will be abnormally lit. Fault diagnosis: the first occurrence of this fault is in the cold weather in the spring, when the mileage was less than 30 thousand km, when the car was sent to the 4S shop to repair it, the trouble was described to the maintenance personnel. The maintenance personnel also asked whether the car had been bumping along the road recently, and whether there was too low fuel level. Because the car has been running in Beijing, the road is better, and there is no experience of driving too little fuel. At that time, the maintenance personnel checked with the fault detector, and the malfunction code was P0300------, which detected a cylinder fire. So the maintenance personnel cleared the fault code, and after commissioning, the engine worked normally and accelerated. Due to the mileage of nearly 30 thousand km, after the replacement of spark plugs, clearance of engine carbon deposits, and cleaning of oil and lubricating systems, the car left the factory. But the car came out of the factory less than 5000 km, this time has entered the summer, the engine again appeared the above "fire" failure phenomenon, again to the 4S store maintenance, 4S store after inspection that the ignition coil needs to be replaced, but soon after the replacement of the ignition coil, the above fault appeared again. The whole process of the "fire" failure of the engine is reviewed. The vehicle has good road conditions, the fuel supply system is normal, the high-pressure ignition coil, the spark plug and other parts are not invalid, and the oil and lubrication systems have been thoroughly cleaned. After careful analysis, the engine spark plug is carefully checked and issued. There is a slight defect between the third cylinder spark plug and the cylinder block, resulting in poor sealing. Troubleshooting: the replacement of the third cylinder spark plug and the seal ring between the cylinder body, after the removal of the fault code after a long time test, the engine "fire" phenomenon did not appear again. Fault analysis: due to the lack of experience of the maintenance personnel, only attention can be made to cause the electrical factors of the engine "fire", the inspection of the machinery is ignored, and the process of assembling spark plugs is not careful enough to find the root cause of the failure. Because the car has been stopped for a long time, the lubricating oil leaks, causing the ignition line to connect, so that the engine appears "fire" phenomenon. Once the engine enters the working state, the engine will evaporate slightly to the spark plug, and the engine can operate normally, so the engine trembling will disappear.