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Driving the mileage of about 142 thousand km in 2008 Changan Ford Fawkes 1. 8L automatic car, the customer reflected that the car engine trouble light was lit during the driving process, but the vehicle did not feel abnormal. Inspection and analysis: use fault diagnosis instrument IDS to retrieve the trouble code to show that the mixture is too thin. The intake measurement uses the inlet force sensor, and the analysis causes the cause of excessive mixture of gas, including oil, oil pump and fuel injector, MAP sensor fault, oxygen sensor fault, power system control unit (PCM) fault or control line fault, and combustion chamber carbon accumulation. Check the vehicle maintenance records, 1 months ago to do the engine deep carbon removal, full car oil cleaning, air intake system cleaning and three yuan catalytic converter cleaning, so the possibility of eliminating coke can be eliminated. The road test and the normal running of the vehicle indicate that the problem of the oil circuit is less likely. The KAM value of erasable memory is cleared and the engine is restarted. After entering the closed loop operation mode, the oxygen sensor is kept at low voltage. At this time the fuel short-term correction SHRTFT has been increasing fuel oil, when the SHRTFT correction reached the maximum value, the long-term correction LONGFT began to correct the basic fuel injection to achieve accurate injection control. SHRTFT and LONGFT can re learn KAM value according to the current work condition after clearing KAM, which shows that PCM and control circuit are all right. Will the oxygen sensor be polluted to cause the oxygen sensor to respond too low, so that the PCM receives the wrong signal? Replacement of new oxygen sensor, mixture or excessive dilution. Excluding the above possible fault factors, the failure point is mainly concentrated on the MAP sensor. Using IDS to read the data flow, as shown in Figure 1, you can see that the pressure value (atmospheric pressure) of the BARO is lower than the normal value, the normal value should be around 101kPa, and the 2 reading of the data flow shows the different atmospheric pressure values. Will it be the MAP sensor bias caused by metering error? After the replacement of MAP sensor, the problem of trial run still exists. Because the other faults have been ruled out before, only the fuel quality is the biggest doubt. Troubleshooting: replace the original vehicle's gasoline and clean the fuel tank. After clearing the KAM value, SHRTFT and LONFT return to normal. Follow back visit to determine that the failure no longer occurs.