The 2004 car Sonata AT sedan (using 2.7LV6 engine) has a mileage of about 246 thousand km. Failure phenomenon: the user reflects, the use of the night after the use of parking in the parking space for the night, when the second days to go up to drive, the engine start difficult, the need to start many times to the machine, and sometimes the engine power is insufficient, and sometimes even automatically extinguish. Fault diagnosis: after receiving the car, according to the situation of the owner, the engine refrigerator is difficult to start, and the factors that cause the hard start of the engine cold machine are mixed gas or excessive concentration, ignition failure, and fuel supply system failure. Connect HI-SANNER to detect, find the system without fault code storage; then read the data flow, the data are in the normal range; the fuel pressure gauge is checked to check the pressure of the fuel system, it is 350 kPa, normal; the dismantling spark plug inspection, the combustion is not very good, the electrode gap is too large, and also found the cylinder line has obvious breakdown. The phenomenon. After obtaining the customer's consent, the spark plug and the cylinder dividing line were replaced, and the injector was cleaned. Because of intermittent failure, the customer will try the car together after installation. During the trial run, it was found that when driving on uneven roads, it sometimes felt that the fuel supply was insufficient. So the fuel supply system is examined. First turn over the rear seat cushion, pull down the fuel pump assembly line side connector, check the fuel pump to catch the wire, normal, check the fuel pump power line (gray), the voltage on the battery is normal. So the fuel pump assembly was removed and burned marks were found at the terminals of the fuel pump connector terminals above the fuel pump assembly. Troubleshooting: replace the fuel pump, and then the test found that the above failure phenomenon disappeared. Fault analysis: the main reason why the car is sometimes difficult to start is that the connection finger terminal of the fuel pump assembly is burnt, and the connector terminals are sometimes exposed to bad contact in the hot state, so it can not provide the required working voltage for the fuel pump, so that the engine will sometimes break oil. When the failure is summarized, the customer should be carefully taken to describe the failure phenomenon, and the whole process of the failure should be carefully inquired, and the cause of the failure should be analyzed in combination with the occurrence of the fault. For example, when the vehicle is running, the engine suddenly fails, and the ignition system usually fails. After the vehicle is running, the engine will stall. But after the engine is waiting for a certain time, the engine can start the engine again, so the fuel system should be focused on. During the maintenance process, various factors are carefully analyzed, and there are certain rules for failure.