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In the 2014 year with a mileage of about 10 thousand km, the imported Ford sharp (EDGE) 2 L sport utility vehicle is produced. User response: the car can not start the engine successfully once it has finished gasoline at the gas station recently. It must start 6~7 times before it can start successfully. After the engine starts, the vehicle is running normally, and the instrument has no fault alarm lights and fault information instructions. When the engine is started again after the fire is extinguished, the engine can start smoothly without any difficulty in starting. Inspection and analysis: after the vehicle enters the store, the author uses the fault diagnosis instrument IDS to test the vehicle system for the failure reflected by the user, and the system has not found the fault code. In order to verify the failure phenomenon described by the user, the author drives the vehicle to the gas station with the user to see if the problem is reproduced when the engine is difficult to start after the oil is added. When the fuel tank is filled with oil, I try to start the engine. It is found that the battery power is sufficient and the starting machine runs forcefully, but the engine can't start successfully. After 30s stopped trying again, it was still unable to start the engine successfully. After 6-7 attempts, the engine was successfully activated when the accelerator was last stepped. According to the above results, the author analyzes the fault points that may involve the fuel supply system, the EVAP control solenoid valve of the fuel evaporation control system, the engine control unit PCM, and the related sensors and actuators. For the engine to start the engine to the end of the engine can be successfully started this phenomenon, the author first diagnosis is to enter the cylinder combustible gas over concentration caused by the fault is in the fuel tank after the oil injection occurs, will be affected by the fuel vapor? So the author consulted the Ford EVAP system roadmap. The fuel vapor in the fuel tank is passed through the carbon canister and then through the hard plastic fuel vapor inlet pipe, which is connected to the fuel evaporating and discharging carbon tank purifying control solenoid valve. This valve is usually closed, and its opening is controlled by the duty ratio signal of PCM, and then the fuel vapor is introduced into the intake system through a rigid plastic pipe. According to the working principle of EVAP, when the fuel is injected into the fuel tank, a large amount of gasoline vapor will be produced in the fuel tank because of the flow of gasoline. A good sealing EVAP system will not introduce a large amount of fuel vapor into the intake manifold to enter the combustion chamber. According to this idea, the author dismantled the fuel evaporating carbon tank purifying control solenoid valve, and found that the solenoid valve has been mechanically damaged, and the valve is always in a constant open state and is not controlled by the control (duty ratio) of the pulse width modulation signal of the PCM. Therefore, when the gasoline is added to the fuel tank, a large number of gasoline vapour can control the electromagnetic valve into the intake manifold by the damage caused by the damage, which causes the excessive mixture of gas (upper limit of combustion), and the failure of the engine to start. Troubleshooting: replace EVAP fuel evaporative emission carbon tank purification control solenoid valve, troubleshooting.