Failure phenomenon
The idle speed of a Jetta 2v automatic gear is intermittent unstable and high. The owner said that he had changed gasoline pump in other repair shops, but the fault was still not solved. When he came to our factory for repair, we first read the fault code by computer, I didn't report the code. I felt the exhaust from the car with my hands. It was very uniform. It was cleaning throttle. I made basic settings. I tried the car with the owner and went out for 2 hours. The Fault didn't appear, I thought that the fault was eliminated. The owner said that the car was a bit fuel-consuming. We used exhaust analyzer to test the combustion efficiency of hydrocarbon 400 (one thousandth) by 13(%). It was OK to remove the spark plug gap and jump the fire direction, change the high-voltage line, test HC down to 100,CO2 increased by 15(%) at this moment, the car suddenly jittered. After we plug in the decoder to read the data stream, the fault of the car disappeared, we didn't see the data of vehicle jitter. We connected the gasoline pressure gauge and shook the car. The oil pressure was very stable. When the idle speed was stable, we read the data stream. After finding that the ignition angle of advance was somewhat held, looking at the timing data (28-87), the oxygen value fluctuates back and forth from 0.2 to 0.8, and the oxygen 0.5% does not find that the mixer is too thick than too thin. Data analysis shows that the computer intends to reduce the engine speed, the data recording function is used here to wait for the occurrence of the fault. The data flow when the fault is caught is as follows;
Fault Analysis
The idle jitter and rotating speed caused by abnormal MAP sensor data are too high. Throttle gate and the injection pulse width and ignition angle of advance are compensated and reflected. Through tail assay, the failure of ignition system is eliminated, combined with gasoline pressure gauge to eliminate the fault of oil pump, through data analysis MAP data exception, the fault point may be vacuum system of the engine, and MAP sensor failure.
Troubleshooting
Check vacuum system, hear the abnormal sound of the check valve leading to the air conditioner, the engine failure begins to appear, replace the check valve, and vacuum tube, and troubleshoot.
