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A 2012 mile KIA speed limousine with a mileage of about 31 thousand km and a 1.6L engine. Customer reflection: the car engine is not easy to start. Fault diagnosis: when the customer complained that the car started the engine after one or two hours, it was not able to start at once. It often needed to start two or three times before the engine could be started. After the repair, the maintenance personnel repeatedly start the engine, the engine can be started smoothly, due to the failure of the need for a certain time interval, so at that time and the customer to negotiate the problem of maintenance time, after the customer agreed to leave the vehicle to the store for inspection. The maintenance personnel put the vehicle in the workshop for about two hours to start the engine again. When the engine started for the first time, the engine did not start, and the engine could start at the second start, but the engine was shaking for a few seconds at the beginning of the car, and after that few seconds the engine was running very smoothly. The first intuition of the maintenance personnel on this kind of fault is that the fuel pressure is insufficient at the start of the engine. In order to prove the intuition, we connect the fuel pressure gauge to the car's oil road. After starting the engine, the fuel pressure is kept at 330kPa, as shown in Figure 1. After the engine is extinguished, the internal combustion pressure of 10min can remain within this range, but as time goes on, the value of the fuel pressure gauge begins to decrease slowly. After about an hour, the value of the fuel pressure gauge is almost close to. As shown in Figure 2. This phenomenon indicates that the fuel system can not maintain pressure continuously, possibly due to fuel pump pressure relief, fuel injector leakage and fuel filter leakage. Considering that the mileage of the vehicle is only 30000km, the leakage of the fuel injector may not be large. So the maintenance personnel focused on the fuel pump and fuel filter assembly. Like many of today's cars, the fuel pump and fuel filter are installed in the fuel tank. When the maintenance personnel disassemble the fuel pump and the fuel filter assembly, it is found that the sealing ring between the fuel pump and the fuel filter has the phenomenon of extrusion deformation (as shown in Figure 3). After replacing the seal ring, the fuel pressure is retested, and the pressure can be maintained continuously and the failure is excluded. The car is caused by the failure of the fuel pump and the fuel filter in the replacement of the gasoline filter because of the negligence of the assembly.