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A Shanghai general Chevrolet (EPICA) SGM7202SE car, using the L34 2 L engine and automatic transmission, is not easy to start in the morning, but once the starting machine is basically normal. The spark plugs were removed and the spark plug electrodes were found to be flooded with oil, and the electrodes and ceramics of the spark plug attached a layer of carbon black, indicating that the mixture was too strong. The car only ran 18 thousand km, and the wear and tear of engine parts would not be very serious. There are several possible reasons why the mixture is too strong: one is too high pressure of the fuel system or the tight seal of the injector; two is the inaccurate signal of the intake manifold absolute pressure (MAP) sensor; the ECT sensor signal is mistaken; the four is the intake temperature (IAT) sensor and the environmental temperature sensor signal distortion; five The fuel injection pulse width is too large or spark plug ignition energy is insufficient; six is the fuel vapor activated carbon tank purge solenoid valve normally open. First of all, spark plug fire test, found that 2 of the spark is weak, so the 4 spark plugs are better, and then the engine is not easy to start, the engine is not easy to start, the engine is starting many times, the idle speed is about 10 min after the engine is extinguished, then the spark plug is removed and checked, and the electrode and ceramic body are still found to still be found. It's a layer of carbon black. It is further proved that it is caused by the excessive concentration of mixed gas. Then connect the fault detector, read the fault code, and result in the trouble free code storage of the engine system. The pressure of the fuel system is measured at about 320 kPa, and the pressure drops slightly after holding 40 min. Then the data flow is read, and the fault detector shows that the relevant data of the engine at idle speed are as follows: the absolute pressure of the intake manifold is 37 kPa, the signal voltage of the absolute pressure sensor of the intake manifold is 1.22 V; the coolant temperature is 32 c, the temperature sensor signal voltage of the coolant is 3.14V; the intake temperature sensor displays the intake air. The temperature is 3 C, the signal voltage is 4.36 V, when the intake temperature is 7 C, the signal voltage is 4.04 V, and the signal voltage is 3.98 V when the inlet temperature is 9. No matter how the external temperature changes, the ambient temperature is shown to be 9 centigrade; the injection pulse width is 3.2 MS; the fuel vapor live charcoal tank is closed. Refer to the data of general Jing Cheng sedan, the rest are basically normal except for the ambient temperature values. After consultation, the sixth reasons are most likely. Then the fuel steam activated carbon tank was removed by the solenoid valve, and the test was carried out. The valve was both two-way ventilation. The valve should be closed when the engine was idle, that is, it was not ventilated, that is, the fuel vapor was not involved in the combustion. Only at middle and high speed this solenoid valve is opened to make the fuel vapor to burn. If the engine is involved in the idle condition, it will have sufficient concentration control at idle speed, plus excess fuel vapor, which will make the mixture more thicker at start and idle speed, and then cause the cooler not to start and start easily. After the machine, a layer of carbon black is attached to the electrode and ceramic body of the spark plug, indicating that the trouble is here. On the morning of the second day, under the condition of engine coolant, the fuel gas steam activated carbon tank purify the vent pipe of the solenoid valve, and then start the engine test. The first time still did not start the machine, but there is a clear sign of fire, the result is still starting several times to start the machine, in addition to this, the car still has other faults. Then read the data flow with the fault detector, this time shows an unexpected message: "the history of the fire record 2 cylinders." So the high voltage line is pulled down from the ignition coil and measured with the multimeter. The resistance is normal; the ignition coil is measured. The results of the 1, 4 cylinder ignition coil resistance are 529 kn, and the 2 and 3 cylinder ignition coil resistance is 5A3 kn. Refer to the training manual of Shanghai general purpose station, without the resistance data of ignition coil. But it is certain that 1 of these 2 ignition coils are abnormal, because the difference between the resistance values of the two coils is 140n, which does not meet the design requirements. Then the ignition coils of two models of Shanghai general Kai Yue and the Great Wall pickup were measured, in which the 1, 4 cylinder ignition coils and 2 and 3 cylinders of the 2 and 3 cylinder ignition coils were 4.60 kn and 4.61 kn respectively; the 1, 4 cylinder ignition coils and 2, 3 cylinder ignition coils of the the Great Wall pickup trucks were 4.93 kn and 4.92, respectively. Kn. Therefore, it can be concluded that the ignition coil of the car has a problem. Because there is no data on the hand, the standard resistance values can not be found. It is possible that the 1, 4 cylinder ignition coils have interturn short circuit, or the 2, 3 cylinder ignition coils and the connection columns, so that the resistance becomes larger. Because the ignition coil of the Kyi sedan car is three line type, and the the Great Wall pickup car is four line type, then the ignition coil of the the Great Wall pickup truck is installed on the fault car, then the 4 platinum spark plugs are replaced, then the engine test is started, and the engine is successfully started. And it runs smoothly. From the above data stream, it is also found that the ambient temperature sensor is defective and needs to be replaced. After replacing the ignition coil and the ambient temperature sensor, the above trouble is completely eliminated.