Inspection analysis shows that the engine has high pressure when starting the engine, but the injector does not fuel oil; check the ignition timing, no mistake; measure the crankshaft position sensor, camshaft position sensor, throttle position sensor, cooling liquid temperature sensor and so on. It is normal. Replace the same type of engine electronic control unit and ignition module test, the failure is still. Check the connection between all sensors and the engine electronic control unit, and the power supply and the grounding of the engine electronic control unit are all normal. After analysis, it is believed that the inspection emphasis should be placed on the crankshaft position sensor, and when the rotor of the crankshaft position sensor is found, the rotor is installed behind the crankshaft timing gear, and it has been found that the rotor has dropped 2 teeth and has the trace of welding. The crankshaft position sensor signal generator rotor teeth can not be used to repair the tooth, because the metal material in the rear welding is different from the other metal materials, and the magnetic induction intensity is not the same, so the signal waveform of the crankshaft position sensor has the wrong waveform. After the engine electronic control unit detects the wrong signal of the crankshaft position sensor, it will inevitably cause the engine to work badly and even the engine can not start. Remove the crankshaft position sensor signal generator rotor.