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Faulty phenomenon, a FAW new Mazda CA7231AT, has a displacement of 2.3L and a mileage of 62 thousand km. The engine failure lights suddenly lit up, and then the lights were always bright, but the driving performance was basically unaffected. When the speed is accelerated from 700r/min to 900r/min, the operation is stable and the acceleration performance is basically normal. There is no exception in the use of the user reaction vehicle. It has been more than 20 days since the failure. This is the first time to repair. Fault diagnosis 1. vehicle basic inspection and inspection visual inspection found no abnormal connection of the wiring harness connector and pipeline connection of the engine. WDS detects that the fault code is P2188-PCM: the fuel system is too high at idle speed. The data is taken as shown in Table 1. 2. fault code analysis (1) the mechanism of generating fault codes: at idle state, fuel system closed control, PCM detection of long-term fuel correction value and short-term fuel correction value, such as exceeding the standard value, then PCM thinks that the fuel system is high in the mixture gas concentration at idle state. (2) the fault codes are caused by the damage of the pre oxygen sensor; the high pressure of the fuel system; the MAF fault; the malfunction of the charcoal tank solenoid valve (Chang Kai); the PCM fault; the fire of a certain cylinder. 3. data analysis, according to the data obtained and the injection time, PCM can adjust the lower limit of the standard value after detecting the large mixture concentration. The short and long term correction values are negative, indicating that the mixture gas concentration in the idle state is high; the adjustment range of the front oxygen sensor is large, indicating the abnormal mixture of gas or the self damage of the oxygen sensor. The other data are basically normal. Using WDS to measure the value of the valve actively, close the carbon tank solenoid valve, and the data has not changed, thus eliminating the usual failure of the carbon tank solenoid valve. Exhaust gas value analysis shows that carbon dioxide is 15% indicating that the combustion condition of the engine is normal. Hydrocarbon 13ppm indicates that the mixture is abnormal. It also excludes the cause of the cylinder fire. Judging from the above analysis, it is possible that the former oxygen sensor is damaged and the fuel system pressure is high. But after replacing the oxygen sensor, the value is still unchanged; the pressure of the detection fuel system is also normal (4.0kPa). At this point, according to the failure code data, we could not find the fault location, but we saw another fault phenomenon of the engine: jitter. Engine jitter is caused by uneven cylinder operation. That is, there are differences in the three aspects of ignition, fuel injection and compression pressure. So the basic test of the engine. 4. the basic testing of the engine (1) when testing each cylinder, each cylinder works; (2) dismantling the spark plug, after the diagnosis in front of the test, doubting the damage of the nozzle in the spark plug of the one cylinder; (3) measuring the resistance of the nozzle, in turn, 5 Omega, 15 Omega, 14 Omega, 15 Omega, indicating that the resistance of the one cylinder nozzle is small; (4) using the waveform to detect the oil spray waves of each cylinder. Shape. First cylinder waveform: low voltage amplitude and long opening time. Other cylinder waveform: waveform consistency, higher than a cylinder voltage amplitude, open time is short. Troubleshooting from the above diagnosis analysis: as the one cylinder nozzle has small blocking value, it is easier to open early and close later than the other jet nozzle under the same voltage control. The injection time is increased and the mixture gas is too strong. The replacement of a cylinder nozzle, the fault can be eliminated. Maintenance summary oscilloscope plays a very important role in modern vehicle maintenance. It should learn and use it well.