◆ text/Jiangsu Ma Wei Lu Jianping
Failure phenomenon
A 2016 Volkswagen New Jetta 1.6L, equipped with compressed natural gas CNG/gasoline hydrocarbon engine, EA211(EU4), CUCA engine, power: Natural gas 70kW/5 600r/min, gasoline 81kW/5 800r/min, mileage 95 000km. Starting the engine to turn KAKA straight, I feel that there is a car phenomenon, but the vehicle cannot start. The car had replaced the oil and oil filter in a repair store. On the 3rd day, there was under body oil mark after the vehicle was turned off. The car was immediately dragged back to the original repair store. The result of the inspection was oil leakage from the engine filter. Remove the oil pan ablassschraube, only put down about 1L of oil (the car should add 4.2L of oil), only add oil again to change the filter, but the vehicle can not start all the time, then drag the vehicle to our place for overhaul.
Fault diagnosis and remove
First, connect the VAS-6150B diagnosis equipment and report the fault code in the engine control unit (Figure 1).
From this fault code, it can be known that the fault is basically caused by incorrect timing of gas distribution, so the engine timing should be repaired and special positioning tools FT10447N1 and T10340 (Figure 2) should be used. Pay special attention to the fact that FT10447N1 and FT10447 cannot be mixed, otherwise the proofreading timing is wrong.
After removing the ignition coil and spark plug of cylinder 1, a long screwdriver (screwdriver) can be inserted into a cylinder and can touch the top of the piston (maintenance manual should be used to determine according to the requirements of dial gauge) remove the rear of the vehicle cylinder (similar to the Bolt of the ablassschraube model) and screw T10340 in (figure 3).
Rotate the engine along the running direction to the limit position and observe the change of screwdriver position. At this time, the crankshaft cannot rotate forward any more. Remove the rear cover of the intake cam, then remove the shell of the water pump pulley, and use special tools FT10447N1 to fix it without removing the water pump belt (Figure 4).
Disassembly timing cover check timing mark (the new car is marked with painting pen when it leaves the factory, Figure 5) It is found that the timing has been reinstalled and the current position is not in the correct position, the timing of the timing belt must be reinstalled according to maintenance manual.
For good timing, after the installation is completed and the vehicle is started, it still cannot be started. Check the engine electronic control system. The static fault code in the engine control unit changes to occasional at this moment. Can you understand whether the valve timing is installed correctly, so what other factors cause the engine to fail to start? The reasons are as follows:
1. Spark plug does not ignite;
2. No oil injection nozzle;
3. Fuel pump relay does not suck;
4. There are still some incorrect points in timing phase;
5. Crankshaft position sensor failure;
6. Fuel pump failure;
7. Engine control unit failure, etc.
Check and replace the above parts one by one, and the vehicle still cannot start. At this moment, the maintenance depends on the deadlock. For this reason, we discussed that since there is electricity and fire, the gas distribution timing mark is right again, then the engine machinery is not carefully checked, and it needs to be deeply checked, the proposal and the components that directly cause incorrect timing phase need to be checked, that is, the camshaft is especially doubtful.
Therefore, disconnect the CMP camshaft position sensor G40 plug with a try first, and the starting vehicle still cannot start. Compared with other vehicles, unplug the G40 plug, which takes a longer start time, but it can still start eventually. Does CMP camshaft position sensor signal trigger wheel have angular displacement deviation relative to its axis? In order to make it clear, we specially removed the camshaft frame valve cover of the faulty vehicle and compared it with the camshaft frame valve cover of another normal vehicle of the same type, and fixed its two camshafts with special tools, it is found that the position of the flange triggered by G40 sensor is obviously angular deviation (figure 6).
Since the camshaft cannot be replaced separately, only the valve cover assembly with camshaft can be replaced, and the vehicle can start normally and run normally after being reloaded.
Maintenance summary
CMP camshaft position the sensor adopts Hall element. When the trigger gear on the camshaft passes through the front end of the hall sensor, the magnetic field changes, resulting in Hall voltage being transferred to the engine for electronic conversion into the control unit, which is mainly used to judge the cylinder signal.
Then why does the trigger wheel on the camshaft produce angular displacement, which arouses our curiosity. We want to CMP camshaft position the mechanical processing technology of the sensor trigger wheel, because the wheel is mechanically pressed on the camshaft, if the engine has a quantitative oil leakage, the oil above the valve cover is very small, and the temperature rise and change in the area on the camshaft occurs, the thermal expansion coefficients of the two mechanical materials of the trigger wheel and the camshaft are different. Although the trigger wheel does not receive external force, the camshaft is driven by the timing belt and compresses the valve through the cam curved surface, it may cause angular displacement of the trigger wheel relative to its camshaft, resulting in the above failure. The above analysis may not be correct, please give advice to the maintenance colleagues.
According to the meaning of the engine fault code P0016, the author suspects that there may be a problem with the engine valve timing, and the diagnostic thinking is correct. However, after the valve timing adjustment is completed, the author checks down and takes a detour. Under normal circumstances, an oscilloscope should be used to measure the waveform of the crankshaft position sensor and the CMP camshaft position sensor at the same time. Through the waveform, it can be found that the waveform of the crankshaft position sensor and the CMP camshaft position sensor is out of sync. Since the timing of the gas distribution is correct, the signal is not synchronized, and the cause of the failure is only mechanical components, that is, the sensor triggered flange finally discovered by the author. In this article, I feel that there are several contradictions. One is that the car has been replaced with oil and oil filter, and the car has been turned off on the third day. Why is the timing wrong? Second, the author adjusted the timing of the gas distribution to disconnect the faulty vehicle CMP camshaft position sensor G40 plug, and the vehicle still cannot be started. Compared with other vehicles, the G40 plug can be pulled out to start.
