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Troubleshooting the control unit of Dongfeng well off engine
  • Automotive

An electric fuel injection engine M7 Dongfeng Xiaokang is assembled. Because of the high charging voltage of the engine, the melting line is broken, causing an ignition transistor in the engine control unit to burn out (appearance deformation), and the model is 30028. Fault diagnosis: first, the 30028 is replaced, then the engine control unit is installed on the engine control unit test platform (the equipment is equipped with the special plug of the engine control unit), the power supply test is found, and the burned transistor is found to have no output ignition signal. After testing, the field effect tube is found to drive a letter on the pole. The number of the two field effect tubes is found to have a patch resistor, the identification character is 1000, the driving resistor on the transistor that can output the signal is 6. 5K Omega, and the abnormal driving resistance is 30K omega (measured on the circuit board), and the amplitude of the signal is measured by an oscilloscope, and the discovery of the amplitude of the signal is found by oscilloscope. It is also obviously too low after the resistance, and third of the 1000 patch resistors are found on the circuit board to measure 100 Omega, which is consistent with the normal identification theory, so the analysis holds that the two drive resistors have been burned down, only a lighter and heavier one. After finding two common 125 Omega resistors, it is welded to the circuit board and tested again. It is found that the signal amplitude of the damaged field effect tube has reached 12V, and the field effect tube, which has no apparent damage in appearance, is still not enough, so it is estimated that the field effect tube is also damaged. So, after changing it, the measured waveforms have returned to normal, so the repair is successful. The cause of damage to the engine control unit of the car is due to the high output voltage caused by the "throwing load" effect of the generator in the course of the running process, which burns the electronic components inside the control unit of the engine. This damage is generally easy to damage the power pipe driven by the point fire or the injector. At the beginning, it was found that the power tube on the circuit board burned only one, and the power tube that did not burn also had the output waveform, because the load on the test table was small current load, and the real ignition coil could not be simulated effectively. At that time, the waveform was seen with the oscilloscope, but the amplitude was not enough, and it was not satisfactory. It was realized that with the deepening of the maintenance and the contrast between the two channels, it was found that the waveform of the ignition signal should be a waveform equivalent to the power supply voltage. The last two signals of the ignition channel were referred to each other to find all the fault points. For me, it was also a new point of knowledge - all the engine control. The output signal of a power tube directly driven by a unit should be a square wave with enough amplitude.

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