A leak is also enough to fix enough! The Mercedes-Benz E200 accelerates sharply and has the sound of airflow

Symptom

A Mercedes-Benz E200 CGI sedan with a range of approximately 85,000 km. The customer reported that the vehicle heard the sound of air flow in the car when it was accelerating sharply.

Troubleshooting

Go out with the customer to test the car, confirm the fault phenomenon, and find that when the vehicle accelerates sharply, a “hoo, hoo” air flow sound will be heard in the car, and this sound will exist with the acceleration process until the speed is stable. In addition, through the inquiry of the customer, it was learned that the vehicle had been repaired by accident and the front windshield had been replaced, and the fault phenomenon appeared only after the accident was repaired.

After confirming the malfunction, based on the clues given by the customer, we first suspected that the front windshield was not tightly sealed, resulting in airflow during sharp acceleration, and the airflow sound heard during test driving looked like it was from the windshield on the passenger side. So we sealed the edge of the windshield with scotch tape on the outside, plugged the lower edge of the windshield with a towel in the car, and then went out to test the car, but the failure was still the same. We sealed the gap between the middle net and the bonnet, tested it again, and the fault still existed.

Could it be that there are some gaps in the chassis components, such as deformation of the heat shield, which causes the sound of air flow during acceleration to reach the cab? So we removed the bottom plate and inspected the chassis components, found no abnormalities, and went out to test the car, and the fault phenomenon was the same.

At this time, some colleagues asked whether it would be the sound generated by the air flow when the exhaust pipe accelerates sharply, but the fault phenomenon will only appear when the road is driven and the engine has a load change, and the emergency refueling in place will not appear, if it is caused by the exhaust pipe, it should theoretically appear when refueling in place. But at this time, we also had no direction for the time being, so we had to find another car’s exhaust pipe to replace it. After changing the test, the fault phenomenon is still the same.

After ruling out the possibility of poor sealing of the passenger compartment and the exhaust system, we again carefully analyzed the conditions for the appearance of abnormal noises. The car is equipped with an M271 EVO engine, as long as the speed changes, the engine load increases, even if the speed is low, abnormal noise will appear, and this is just the time for the turbine to intervene in the work, that is, when the turbine is working, the air flow sound will appear. Through analysis, we pinpoint the fault point in the engine’s intake system. So can valuable data be obtained by observing the actual value changes of each sensor of the booster system during the field test, which can be used to aid analysis? So we connected the diagnostic instrument to the road test, but the actual value obtained once again disappointed us, whether it was a sharp acceleration abnormal sound or a stable speed, the actual value of the booster system was normal, there was no abnormality. Although there is no data from the actual values that can help analyze the cause of the failure, we agree that the abnormal noise is generated by the engine intake system. Therefore, we intend to check the components of the air intake system one by one. No problems were found. Replaced with another turbocharger for testing, the abnormal noise is still the same.

Subsequently, we set the target for the charge air cooler, because this component was also involved in the accident repair, so we planned to remove the charge air cooler to check it. When we removed the front bumper, we finally found the problem! There is a cut in the hose connecting the turbocharger to the charge air cooler, just at an angle that is difficult to detect (as shown in Figures 1 and 2).

Figure 1 Hose position

Figure 2 Location of leakage

When the vehicle accelerates sharply and the turbo intervenes, the turbocharger transports a large amount of compressed air to the charge air cooler, at which time the compressed air leaks from the hose and impacts the outside air during driving, resulting in an air flow sound.

Troubleshooting

Replace the hose between the turbocharger and the charge air cooler.

Summary of failures

When dealing with this failure, we really couldn’t find our way at first and took some detours. After hitting the wall, and then carefully analyzed, the vehicle only appeared after the accident maintenance, and it was at the time when the turbine was working, and finally locked and checked the engine’s air intake system, and the damaged parts were found most and troubleshooted. It can be seen that when encountering some tricky faults, inquiring the maintenance history of the vehicle, and analyzing the working conditions of the vehicle when the fault occurs, will often give the idea of “mountains and heavy water doubts and no way”, bringing the effect of “another village”.

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