A Volkswagen Langyi car with a mileage of about 17 thousand km. It is difficult to start the car after a long time of parking. The owner reflected that 4 to 5 engines were started every morning to start the engine, and the engine was unstable after the start of the engine, but after a period of operation, the engine was running smoothly, and the next day the vehicles were running normally. After the car: ask the owner to know that the fault has plagued the owner for a long time. Several repairs before the engine cleaned the engine oil and gas, replaced the spark plug, but the problem was not solved. Consult the owner's opinion and the owner agrees to leave the car in service. On the morning of the second day, the engine was started under the condition of a cold engine, and the engine was started only after starting several engines. Check the air road, oil circuit and circuit in the engine room simply and quickly. Check the fuel pressure, connect the oil pressure tester VAG1318, connect the ignition switch, find the oil pressure meter not moving; find a quiet place to close each car door, listen carefully to the back seat at each switch on the ignition switch, and do not listen to the sound in the back seat. The sound of the oil pump working. (after consulting the information, it is known that the fuel pump of the vehicle is controlled by the engine control unit and is not directly related to the ignition switch. Starting the engine, it is found that the fuel pressure rises slowly and is accompanied by the sharp jitter of the engine. The fuel pressure can be kept at 400 kPa after the engine, and the engine runs back to normal. After flameout of VAG1318, it was found that the fuel pressure dropped to 0 kPa in 30s. Under normal circumstances, the pressure valve integrated in the fuel filter is responsible for the pressure adjustment, limiting the fuel pressure to 400 kPa, the one-way valve in the fuel pump is responsible for the pressure protection, and the 10 min is static, and the fuel pressure should not be less than 250 kPa. According to the test results, the fault of the vehicle is due to the failure of the one-way valve in the fuel pump, which can not keep the normal pressure. The fuel supply is insufficient when the vehicle is restarted for a long time. Troubleshooting: after changing the fuel pump, re measure the fuel pressure indicators (pre supply, oil pressure, pressure keeping condition), all return to normal, troubleshooting.