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Example: an Elysee oil and gas dual purpose taxi was put into operation in 2011. The car starts with gasoline every day, and when it runs normally, it burns natural gas. At the beginning of 2014, the mileage of the car reached 250 thousand km, and it was difficult to start the cold car, but when the temperature of the coolant was normal, the engine could start to start smoothly. Fault diagnosis: the car owner reflects, the car has been to several maintenance points for maintenance, replacement of fuel pumps, spark plugs, cooling liquid temperature sensors, several times cleaning the injector, and even the same type of car changed to the computer, but the fault has still not been ruled out. After receiving the car, the fault code is read first with the fault diagnosis instrument, and the fault code is not found. The cold car start data flow is read, the coolant temperature is 6, the ambient temperature is 9, the injection time is 7.812.8ms, all in the normal range; the pressure of the fuel line is 0.28MPa, and it is normal; check the high pressure fire and the ignition line. On the way, it is normal to suspect that valve carbon deposition causes insufficient cylinder pressure, and cylinder pressure gauge is used to check cylinder pressure. When the cold car starts, the computer determines the injection pulse width of the cold car mainly based on the signal supplied by the coolant temperature sensor. During the maintenance process, the coolant temperature and the ambient temperature shown in the computer data are consistent. And when the engine is started, the pulse width of the cold car fuel injection displayed in the computer data flow is normal. Because the car can not be started many times, the spark plug was removed and the spark plug was almost drowned. It felt the mixture was too strong, but it was found that the intake pipe was tempered when it was started. When the carburetor cleaning agent is injected into the intake pipe, it is able to run smoothly. Once the exhaust pipe of the vehicle is running black smoke and the water temperature is normal, the vehicle is normal on that day. To further inquire the owner, it is found that the vehicle is easy to start in the morning and is reflected in the use of gas without oil. The fuel is also consumed, and the average fuel on the fuel meter is consumed on average every two days. The car only uses fuel when it starts, and the rest time is always using natural gas, so the fuel consumption is abnormal. It is suspected that the injector seal is not well sealed, and the leakage phenomenon is not found again. From the analysis of the fault phenomenon again, the difficulty of starting the vehicle is fuel supply, but the volatility of fuel is even worse, even "drowning" spark plug. Where does oil come from? How does the evaporative atomization of fuel get worse? Therefore, it is possible to judge the failure of the solenoid valve. After the inspection, it is found that the solenoid valve pipe of the carbon tank is in constant state, and the solenoid valve is often pumped into the cylinder when the fuel vapor in the fuel tank is burned. Because of the continuous pumping of fuel steam, the fuel oil in the tank is reduced, the remaining fuel vaporization atomization performance is worse and the cold car is worse, so it is difficult to start the trouble in the morning. After changing the solenoid valve of the carbon tank, the fault is eliminated. Maintenance summary: the activated carbon tank is used to temporarily store the fuel steam inside the tank, reduce the leakage of the fuel steam to pollute the atmosphere and save the energy. The tank is closed structure, the fuel steam is controlled by the vacuum of the carbon tank electromagnetic valve, the temperature of the coolant reaches normal, the engine is in medium load condition and the engine control model is in the medium load condition. The block will pass through the carbon tank electromagnetic valve through pulse width modulation, so that the fuel vapor will burn into the cylinder. In the normal operation of the elyshe cabs, the gas is burned and compressed, and the fuel injected in the tank is mainly used in order to start, and the amount of oil stored is generally very little. Because of the failure of the carbon tank electromagnetic valve, the vehicle is burning with the engine in the cylinder while the gas is used, and the fuel consumption is increased. A small amount of oil and vaporization and atomization in the fuel tank become worse, that is, the quality of fuel decreases and the start-up of cold vehicles is difficult. As the fuel steam is inhaled through the cylinder of the carbon tank solenoid valve, the proportion is very small compared with the natural gas inhaled, so there is no oil and gas mixing in operation, and the fault phenomenon of black smoke is taken when the vehicle accelerates, which brings some difficulties to the fault diagnosis.