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A Honda Acura (ACURA) car with mileage of about 80 thousand km, equipped with G25 A4 engine and automatic transmission. User response: when the engine accelerates, the engine jitter is serious, and there is a shooting phenomenon. Once the spark plug, the ignition coil, the crankshaft position sensor, the top stop position sensor, the fuel injector, the deflagration sensor, the intake pressure sensor, the coolant temperature sensor and the oxygen sensor, etc., but the failure is not excluded. After receiving the vehicle: confirm the fault symptoms, start the engine, idle speed is steady, exhaust pipe has no black smoke, no abnormal phenomena can be seen. When the engine is accelerating, the engine will shake like a cylinder. Road test, low speed vehicle acceleration performance is basically normal, but when the speed is above 90km/h, it will not be able to accelerate. Routine inspection of the engine, including fuel pressure, cylinder pressure, ignition timing and valve timing, is normal. It is doubted that the power system control module has a problem, but the car has a new year, there is no ready-made accessories, can not carry out the exchange test, the replacement in the case of no diagnosis, will cause unnecessary economic losses. The diagnostic system is used to diagnose the power system without fault code. Check the ignition system, use the oscilloscope and ignition timing gun and other equipment to detect the ignition advance angle, ignition sequence, closing angle and ignition time. Check the fuel injection system, including fuel injection timing and injection time. It is found that the fuel injection time is too long when the engine speed exceeds 2000r/min. It can be seen from the maintenance experience that the injection time of the idle and slow acceleration is about 3S when the engine is not running, and the injection time will increase instantaneously to improve the engine's acceleration performance. When the engine runs at a high speed zone, the fuel injection time is not quite different from the idle injection time, but the engine speed is more than 2000r/min, the injection time is above 6S, and the fuel injection will not be reduced again. The fuel injection is too much, the mixture gas is too strong and the combustion is not complete, this is the engine acceleration jitter, no The direct cause of the force. Combined with the principle of electronic control engine, the power system control module calculates the injection time according to the signal of engine speed, load and related sensors. Then the concentration of mixed gas is judged according to the oxygen sensor signal, and the closed loop control of the mixture is carried out. Check the relevant sensors and wiring connections, and found no abnormalities. Replace the oxygen sensor, the failure is still. Based on the above maintenance results, it is considered that the cause of the failure is the damage of the power system control module. The replacement treatment is carried out, and the failure is completely eliminated. The power system control module is a precise and complex electronic assembly component, and its fault is difficult to judge. This is also the difficulty of this case. The repair work of the power system control module requires considerable theoretical knowledge and maintenance experience of the maintenance personnel. For most maintenance personnel, if it is possible to determine the problem of the power system control module and replace it correctly, there is no need to repair it. Therefore, the focus of maintenance work is to check whether the external lines, sensors and actuators are good. At the same time, we can correctly use the diagnostic equipment to find out the cause of the failure. It is possible to avoid misjudgement when changing the power system control module after confirming that there is no external problem.