Passat AVF: Squealing or Hissing Noise?

Dear community!

First of all, I'd like to mention that this is my first post, and I'm just a beginner. So please bear with me if I make mistakes from time to time, and everything I explain might be very basic!

Regarding my issue:

"The car makes strange grinding or hissing noises when accelerating, specifically in second gear from approximately 1200 RPM to around 2600 RPM, where the noise is very noticeable. The noise increases with acceleration. My initial thought was a turbocharger! A friend of mine checked the turbocharger, and he confirmed that there's no play in the turbine and no damage on the intake side. So, I don't think it's the turbo. Also, I've been driving with this noise for about 30,000 kilometers now. Furthermore, it doesn't consume any oil. Please correct me if I'm wrong."
Furthermore, I checked the intake side for leaks to identify any issues in the system, but I didn't find anything.
Another phenomenon with this noise is that when you accelerate fully, you suddenly hear a louder hissing or scraping sound, and then the noise completely disappears! This actually happens in all six gears, within the same speed range. Of course, you don't hear anything when the vehicle is stationary and you give it gas.
Another tip I was given was about the dual-mass flywheel (DMF). However, I don't think that's the problem because the noise seems to be coming from the driver's side, and also, it's difficult to check the DMF, or am I wrong? Besides, I don't experience any jerking when shifting gears.
Ein weiteres Phänomen ist, dass als mein AGR defekt war, das heißt der Motor hat Wellenförmig beschleunigt und dass Geräusch ging auch mit dieser Wellenbeschleunigung mit! DahThe new AGR.
Furthermore, the turbocharger hose once ripped (from the turbo to the metal pipe under the water cooler). The engine then went into limp mode, and since I was on the highway, I had to drive a few more kilometers; of course, with only about 50 horsepower. However, the noise that I mentioned disappeared!
I was also told that it might be the freewheel of the LIM (Linear Induction Motor), as the noise seems to originate from there. I checked the freewheel, at least it rotates and isn't stuck or anything like that!
I'm at the end of my rope with this problem. Could it possibly be the N18 or N75 valves?
I should also add that there are no errors in the memory, the gauges seem to be working as usual, it's not consuming any more fuel than before, and it's not producing any excessive smoke!
I've been following the discussions in this forum for over a year, but I haven't been able to solve my problem. I hope that maybe one of you can give me some advice !

Thank you.


Data: Passat 3GB 4motion (96 kW); Engine code: AVF, Year of manufacture: 2004, approximately 130,000 km.

Have you driven a turbodiesel before?

Can you rule out the possibility that this is just normal turbocharger whistling?

Yes, I've always used Turbo Diesel fuel! It's definitely not the turbo whistling sound; I hear that too, but it's normal for any AVF engine. So, everything is fine on that front!

It might be the electronically controlled throttle (AGR) that isn't working correctly. When you accelerate fully, it closes completely, which could be an explanation. Perhaps the control valve is faulty...

So, should I replace the N18 valve? I'll go to the to get a new part!

Thank you in advance!

I have now replaced the valve, but the noise is still there . I should also mention that the noise is present even when driving at a constant speed of 2000 RPM, but it's not as loud. It sounds like a grinding bearing. When accelerating from around 2300 RPM, you hear a hiss, and then it disappears! If you take your foot off the gas from 2000 RPM, the noise also becomes quieter, or sounds like a failing bearing that is running down until just before 1200 RPM, and then it disappears as well. Does anyone else have any ideas ?

Based on how you're describing it, the noise is most likely coming from the turbocharger itself. Are you absolutely sure there are no leaks in the boost pressure system? Is the turbo's wastegate valve functioning correctly, and does the linkage move freely?

I completely depressurized the intercooler piping with approximately 1.5 bar; there was no hissing or any other noise! The rod moves up and down when you apply a bit more pressure; I can't really say how easily it should move. I'm not entirely sure what you mean by "tack valve"! Are you referring to the N75 boost control valve?
I've also been suspecting it might be the turbo for a while now, but as I mentioned at the beginning, I've definitely heard this noise for over 30,000 km. I've already checked the turbo from the intake side to see if there's any play, both axially and radially. There's no noticeable play. No oil leaks and no soot! So, if it really is the turbocharger, shouldn't it have failed by now? Also, I haven't noticed any loss of power at all!
If I am wrong in my assumptions, please correct me! Thank you.

skydiver_001 wrote:

I've also been suspecting for a while that it might be the turbo, but as I mentioned at the very beginning, I've definitely heard this noise for about 30,000 km. I've already inspected the turbo from the intake side, checking for play both axially and radially. There is no noticeable play. No oil leaks and no soot! So, if it really is the turbo, shouldn't it have failed by now? Besides, I don't notice any loss of power at all!

Loud turbos can sometimes last surprisingly long before they completely fail.

The noise source "charger" (with definitely tight intake passages, including a normally closed EGR valve ) can be identified quite clearly as follows:
Drive in the highest possible gear within the vulnerable RPM range, and gently adjust the accelerator pedal while listening for noises. If the noise changes almost immediately and clearly with the movement of the pedal, then it is a noise related to the turbocharger or its speed.

Thank you, Ulf, for your bike!

I followed your advice! I think the sound changes depending on how much you press the accelerator. You hear it very faintly, but when you give it more gas, the noise gets louder and shifts from a scraping sound to more of a hissing sound. When you floor it completely, the noise disappears!
If it's truly the turbocharger that's failing, and it has lasted this long, how would it fail? Would it simply result in a loss of power, or would it completely disintegrate, causing parts to end up in the intercooler?

skydiver_001 wrote:

The sound, as I think, changes with the accelerator pedal movement. That means you hear the noise very quietly. However, if you give it more gas, the noise gets louder or changes from a grinding sound to a more hissing sound, and when you floor it completely, it disappears!

It really sounds like a turbocharger noise. If it only occurs below a certain RPM, it could theoretically still be pump noises, which should then appear as pressure fluctuations in MWB11 logs or on an LDA.

Quote:

If it's indeed the turbocharger and it has lasted this long, how would it fail? Would it simply cause a loss of power, or would it completely disintegrate, leading to parts entering the intercooler?

Turbocharger noises that vary with engine speed usually (always?) originate from imbalances in the rotating components. If the resulting forces eventually break the turbocharger shaft, small pieces will be produced.
Below the wave breaking load, a loud loader can run for a very long time without any problems.

Thanks again for your reply, ULF!

Does the "Kleinholz" only affect the loader or the engine as well? So, I'll keep driving until the loader gives up!

I had the exact same symptoms and now I've found the cause. It was a faulty gasket on the pipe connecting the exhaust manifold to the EGR valve. The soot buildup was only visible from below. I then temporarily held a cloth in front of it (it got very hot) and had an assistant give it some gas, and the noise disappeared. I replaced the metal gasket and that fixed it.

For the sake of completeness: In engines with a DPF, temperature sensors or the oxygen sensor may also not be properly tightened, which should be checked. The AVF engine does NOT have this issue.

Hello,
We're now experiencing a noise – a whooshing sound – in our Passat 3BG when accelerating, and it seems to be coming from the front right side. It's likely one of the hoses.
He's also making some noise while doing it.
I have already removed the thick hoses; they are dirty, but apparently leak-proof.
Now, directly behind the turbocharger is a pipe connection to the exhaust system, which is covered with a flexible joint and steel cables. I can move this back and forth, and it's definitely not sealed. Should it be sealed, though?
Does anyone have an idea/picture of what other hoses those could be? The turbo has been working reliably so far, with 430,000 km on it - we would like to reach the full 500,000 km .
Thank you.

The flexible part should naturally be airtight; if it is not, you will hear the noises that I described.