The Audi A4L 2.0L-TFSI car with a mileage of about 60 thousand km. The engine idling operation is not stable, and a cylinder is defective. Fault diagnosis: after receiving the vehicle, the Audi special diagnostic instrument is used to detect the engine electronic control unit. It is found that the internal storage of the number 3 cylinder fire fault code is consistent with the engine's idling fault symptoms. According to the fault code generated by the ECU, the maintenance personnel can analyze the possible causes of the failure. 1. engine 3 cylinder ignition system malfunction (ignition coil power or ground bad, ignition coil, spark plug, etc.); 2. supply system of the injection nozzle fault (the nozzle blockage causes mixed vapour thinning, oil spill caused by the nozzle oil leakage caused by mixed vapour, injection nozzle fault, etc.); related data: the latest Audi factory maintenance in 2014 The information system ELSA 5.13. mechanical failure (the engine intake door closure is not strict, the engine exhaust valve closure is not strict, the piston and cylinder wall gap between the excessive pressure in cylinder and so on). According to the above reasons, the maintenance personnel first detected the ignition coil and spark plug of the ignition system of the engine, and found no fault. In order to prevent the internal faults of the ignition coil, a new ignition coil is replaced, but the trouble still exists. Next, the maintenance personnel use the cylinder pressure gauge to measure the pressure of the engine No. 3 cylinder to 11 bar (1 bar=105P a), which is in line with the technical requirements (normal pressure, 0 to 13bar). A special diagnostic instrument is used to check the data flow of the nozzle of No. 3 cylinder. It is found that the injection pulse width of No. 3 cylinder is different from that of other cylinders. The injection pulse width of the other cylinder at idle speed is 1.2ms, and the injection pulse width of No. 3 cylinder is 1.0ms. At this point, the reason for the maintenance personnel to judge the failure of the engine is the injector fault, but after the replacement of the new nozzle, the fault is still not eliminated, the engine idle state still exists the phenomenon of fire deficiency, and the clue of the fault diagnosis is broken at a time. Finally, the maintenance personnel reset all the replacement parts. When starting the vehicle, it was found that there was a slight "dada" noise on the top of cylinder cap 3 during the short time of engine failure. Is the engine valve fault? The valve actuating mechanism of Audi A4L engine valve train is different from traditional engine. In order to increase the volume of fresh air in the cylinder when accelerating, the exhaust camshaft of Audi A4L engine has a variable lift technology similar to Honda valve. In the case of engine acceleration, the exhaust pressure of the engine is increased to reduce the response time of the waste turbocharger. In addition, in order to reduce mechanical noise, valve actuating mechanism also adopts hydraulic tappet and roller rocker with no valve clearance. According to the structural characteristics of the gas distribution mechanism of the Audi engine, it can be found that if there is a pressure relief in the hydraulic tappet of the engine exhaust door or the axial clearance of the rocker bearing bearing is too large, the exhaust gas of the engine cylinder will not be completely discharged. The increase of the residual amount of the exhaust gas of the cylinder will cause the low temperature of the flame, and the combustion will be produced. The expansion pressure decreases, resulting in engine misfire. In order to verify the above analysis, the maintenance personnel dismantled the hydraulic tappet and rocker arm of the 3 cylinder valve drive device, and found that the hydraulic tappet meets the technical requirements, but the axial clearance of the rocker roller bearing is too large. Replace roller type rocker arm of No. 3 cylinder exhaust valve, troubleshooting. According to the conventional judgement, the ignition system failure, fuel supply system fault and engine compression pressure are insufficient. Through this case, it is not difficult to find that the excessive exhaust gas in the cylinder due to the failure of the valve actuating mechanism will also cause engine misfire. Fault review: in this case, the cause of the engine single cylinder fire is analyzed from the ignition system, the fuel supply system and the mechanical structure of the engine, and the overall fault check is easy to complicated, and the fault is eliminated eventually. However, the author still has the following writing in the case. Several problems are not complete, such as car code, vehicle year, engine model and so on, which can make the reader further verify the technical information related to the malfunction vehicle. The information of the fault code for the cylinder fire failure code is not introduced in detail, such as the fault code number, the condition of the fault code detected by the engine ECU and the engine operating conditions (including the engine speed, load, working temperature, etc.). These information are the important basis for analyzing and judging the cause of the failure and the troubleshooting. Since the Audi 2.0L-TFSI engine valve lift system (AVS) is mentioned in the article, it is necessary to make a simple introduction to the system and not take it as "Honda's valve variable lift technology", because the reader hopes to see the working principle of the relationship with the fault in an article: I do it here. Supplement: the valve lift system of Audi 2.0L-TFSI engine is not used on the intake side, but on the exhaust side. When the engine speed is low, the small cam shape part is used and the valve lift is small. When the engine speed is high, it will switch to the large cam shape part, and the valve lift is large. As shown in Figure 1, two shapes of cam are switched on each cylinder, and two electromagnetic actuators are sealed to complete one executive element to switch from a small lift to a large lift, and the other is responsible for switching from the valve lift back to the lift. If the actuating element is activated by the engine control unit, the metal pin will extend out and insert into the chute of the cam piece to complete the valve lift switch. After the cam switch is completed, the metal pin is pushed back by the permanent magnet in the actuator and a voltage is induced in the excitation coil of the electromagnet when the metal pin is pushed back. This voltage signal is received by the engine control unit as a feedback signal for the successful switching of cam parts. The small cam shape part will delay the opening time of the exhaust valve. This can effectively prevent the reflux of exhaust gas when the valve overlaps, and effectively eliminate the residual gas content in the cylinder with the advance of intake. This improvement not only significantly improves the response characteristics of the engine, but also significantly improves the output torque of the engine at low speed.