A Buick sedan with a mileage of about 24 thousand km. Customer reflection: the car has been a few days before the idle speed is unstable, high speed driving speed is not smooth fault, to this check, found that the injector plugging, after cleaning the effect is good. However, two days later, this fault occurred again, and the engine indicator light was shining, and refueling at high speed was also boring. Fault diagnosis: according to the phenomenon provided by the customer, first connect the special detection instrument TECH2 of the General Company to get the fault code. The main operation steps are: (1) the main menu selects the diagnosis, and then press "enter" (confirm) key. 2. Select the power assembly in the system menu. Then press the "enter" key. Select the fault code and press the "tente" key. (4) select the DTC information, and then press the "enter" key. Related information: in 2013 Buick Junwei original factory maintenance manual on the screen immediately show the fault code P0300, its meaning is to detect the lack of engine cylinder, indicating that the engine in the process of operation, electronic control unit detected a few cylinders have the phenomenon of lack of cylinder. In order to know exactly which cylinder is missing the cylinder, and enter the "special performance" option, then select the "lack cylinder diagram" column, its main operation step (with the above fault code continuous operation): according to the "exit" (exit) key, select "special function", and then press "enter" key to enter, the screen shows a specific lack of cylinder. The diagram is shown in Figure 1. The observation chart shows that the accumulative number of cylinders in the 2 and 3 cylinders is more frequently, and the description is serious. The operations mentioned above can be completed in a very short time, so the testing work is mainly about 2 and 3 cylinders. On the premise of judging its bad work, the system has been tested, including oil pressure supply flow of oil supply system, cylinder pressure and so on. The replacement test of spark plug, ignition coil, high pressure line and so on is done. The result is not found out, and the injector is blocked again. With the question of dismantling the injector again, it was found that the head was full of black carbon, and the 2 and 3 cylinders were particularly serious, and there were "wood chips" like sundries on the upper part of the injector, which almost stopped the inlet. Using the ultrasonic cleaning instrument, the fuel balance test was done. After the basic normal, the fuel line and tank were cleaned, the gasoline filter was replaced, and the No. 93 gasoline was added again. After loading, the test was carried out, the idle speed was smooth and the idle speed was good. However, when the speed reached 140km/h, it continued to fuel and felt the speed was slow, and the engine's voice was stuffy. It seems that the problem was not completely solved. Once again, use TECH2 to adjust the code and trouble free code. Careful analysis of the causes of high speed is not only the following: (1) the air filter is clogged and the air intake is reduced. The oil road is blocked and the oil intake is reduced. The exhaust is not smooth and the power is reduced. 4. The throttle can not be fully opened, and the engine is not full load. Compared with the vehicle, the possibility of blockage of the exhaust system is great. Shake the front section of the exhaust pipe (with a three element catalytic converter), and there is a loud crash. Replace the three yuan catalytic converter, test again, and remove the bottom of the fault when running at high speed. Failure analysis: because the customer does not according to the manufacturer's stipulation, use the gasoline with high lead, make the injector plug, and also cause the three yuan catalytic converter "poisoning" to fail, and cause this fault.