Diagnosis and analysis of automatic engine flameout
heavy truck
Treatment method of vehicle encountering water
Key points of engine fault diagnosis

Common fault causes

  1. Vacuum leakage of intake pipe.
  2. Unstable idle speed caused by improper idle speed adjustment, dirty throttle body, poor idle speed control system, etc.
  3. The fuel pressure is unstable, such as excessive wear or poor contact of the brush of the electric fuel pump, or blockage of the filter screen of the fuel pump, etc.
  4. Exhaust gas recirculation valve is blocked or bottom leakage.
  5. The fuel pump circuit, fuel injector drive circuit and other circuits have poor contact and other faults.
  6. The fuel pump relay, EFL relay and ignition relay are defective.
  7. The ignition system is not working properly. For example, the high-voltage spark is weak, the spark plug has been used for a long time, the ignition timing is not right, the ignition coil has poor contact or there is a turn to turn short circuit in hot state, resulting in no high-voltage spark or weak high-voltage spark, poor contact of low-voltage line, damage of insulating glue, intermittent grounding, etc.
  8. Poor throttle position sensor.
  9. The air flow meter or intake pressure sensor is faulty.
  10. The coolant temperature sensor and oxygen sensor are faulty.
  11. The crankshaft position sensor has faults, such as no speed signal (the plug is not inserted properly, the signal wire of the crankshaft position sensor is broken, the positioning screw of the sensor is loose, the gap is out of balance, the sensor is damaged, etc.); The broken teeth of the signal ring gear of the crankshaft position sensor will cause the flameout during acceleration; The poor temperature stability of electronic components in crankshaft position sensor will lead to abnormal signal and intermittent flameout.
  12. ECU is faulty.


General steps of fault diagnosis

  1. Carry out fault self diagnosis first and check whether there is fault code. If yes, find out the cause of the fault according to the displayed fault code. Pay special attention to whether the sensors and actuators (such as engine speed and crankshaft position sensor, camshaft position sensor, coolant temperature sensor, throttle position sensor, idle control valve, etc.) that will affect the changes of ignition, fuel injection, idle speed and valve timing are faulty.
  2. If the automatic flameout only occurs at idle speed and can be started immediately after flameout, it can be checked according to the unstable idle speed and easy flameout (see the inspection procedure of unstable idle speed and easy flameout).
  3. Use the fault simulation symptom method to vibrate the fuse box and each line connector to see if the fault can occur. Then further check the harness connector for poor contact, each grounding wire for poor grounding, and visually check the harness insulation for damage and intermittent grounding.
  4. Change the working environment temperature of ECU and igniter by using fault simulation symptom method to reproduce the fault and then diagnose the fault cause.
  5. Try to replace ignition coil, spark plug, etc.
  6. During continuous test run, use multi-channel oscilloscope to monitor engine speed and crankshaft position sensor, air flowmeter, 5V output reference power supply voltage of computer and other signals at the same time.
  7. If there is surge and poor acceleration before the flameout, and then the flameout slowly, the fault may occur in the poor oil supply. The fuel pressure gauge can be connected. It’s better to fix the gauge on the windshield with transparent glue, and then test it. If the oil pressure is too low during flameout, check the fuel tank, electric fuel pump, fuel filter, oil pressure regulator and fuel pump control circuit.
  8. During the test run, connect the special diagnostic instrument, read the data before and after the fault, and carry out comparative analysis, so as to find out the fault.
  9. Check and eliminate the faults one by one.
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