T6.1 engine noise and poor dealer service

[Pedro20001]

Hi all, after advice with an intermittent engine noise (see YouTube below) which is heard after driving, engine warm at idle for about 10 seconds then stops. After a slight rev increase it goes and may not come back. It has been into the dealers 3 times; I did have an engine light on with code P0325 knock sensor which has been replaced today. The dealer has also left me with a bad vibration when engaging reverse so back again for that and the noise in the YouTube link is still there! Has anyone any idea of this noise as it is not only worrying but the dealers are unsure too. Thanks in advance. edit...apologies for the rubbish YouTube link! Update - the AA chap who came out last night to investigate the vibration listened to it and said possible fuel pump? Anyone got any suggestions as I am rapidly losing faith in MOTUS Derby

 

[bluezie]

Sounds like a noisy tappet, but hard to tell as it's gone by the time you're filming in the engine bay. Whatever's causing it, it's upper engine, because the tapping is at half engine speed, ie cams, pump, injectors.
A sticking hydraulic compensator can make tappet noises come and go, when the oil is gradually squeezed out, then it suddenly pops back again, and the noise disappears.

 

[Pedro20001]

Thanks for the reply, certainly makes sense. I sometimes get a ticking noise on a cold morning from the top end which goes after a few seconds which does sound like a hydraulic lifter. When the above noise happens it will always do 4 taps then pause and then repeat 4 times then stop. It is quite bizarre! Surprisingly VW haven't heard it before so are reluctant to investigate, unless I pay of course but as it's got 2 more years warranty I don't see why I should.

 

[DXX]

Maybe a defective auxiliary belt tensioner?

 

[mmi]

Got a bit curious so made a couple of plots - not sure if they are useful but anyways here they are...

Repetition interval of tapping​

In the picture on top spectrum plot, below signal amplitude (youtube sound track) graphed.
Highlighted portion (2.585 - 3.017 seconds) contains three full cycles = 432 ms. Thus repetition interval is 144 ms which gives us 417 taps/minute - which matches engine idling at 834 RPM.

When the above noise happens it will always do 4 taps then pause and then repeat 4 times then stop.

That's quite interesting - indeed there are 4 (and some) taps and a fade between. However, a spectrum plot below seems to suggest there might be actually more but some just not clearly audible. See orange vertical lines on purple background.

Spectrum plot - count of taps​

As the tap is actually a short impulse type of signal it will spread out all over the spectrum - which is easier to "see" in frequency domain. Below plotted signal spectrum from 0 Hz to 19 kHz. The impulses/taps stand out can as orange lines on purple background. Amplitudes are scaled by colour - yellow (high)-orange-purple-black (low).


As it seems that Forum shrinks image-files, attached the spectrum plot also as PDF for better viewing.

[Amplitude plotted on linear scale, spectrum plot on mel scale]

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What's the engine code - it's printed on configuration sticker under dash in driver's footwell.

 

[Pedro20001]

I'll post it monday, it's back in the dealers as when they changed the knock sensor they haven't done up the engine mount correctly so that's the cause of the vibration sorted. Not a happy bunny. Spoke to the master technician! Says could be dual mass related as if the engine detects a vibration the ecu will inject more fuel in the engine to try and counteract it. Does this make any sense or is it crazy talk? I do suffer from occasional clutch judder and vibration.

 

[Pedro20001]

I'll post it monday, it's back in the dealers as when they changed the knock sensor they haven't done up the engine mount correctly so that's the cause of the vibration sorted. Not a happy bunny. Spoke to the master technician! Says could be dual mass related as if the engine detects a vibration the ecu will inject more fuel in the engine to try and counteract it. Does this make any sense or is it crazy talk? I do suffer from occasional clutch judder and vibration.

I really appreciate everyone's replies and help in this, hopefully it will be sorted soon

 

[Simondo]

Sounds like the dual mass flywheel Death rattle to me.

 

[Fozzer]

Just a question what age is the van, mileage, have you had it from new ?

 

[Salty Spuds]

Got a bit curious so made a couple of plots - not sure if they are useful but anyways here they are...

Repetition interval of tapping​

In the picture on top spectrum plot, below signal amplitude (youtube sound track) graphed.
Highlighted portion (2.585 - 3.017 seconds) contains three full cycles = 432 ms. Thus repetition interval is 144 ms which gives us 417 taps/minute - which matches engine idling at 834 RPM.

View attachment 179680


That's quite interesting - indeed there are 4 (and some) taps and a fade between. However, a spectrum plot below seems to suggest there might be actually more but some just not clearly audible. See orange vertical lines on purple background.

Spectrum plot - count of taps​

As the tap is actually a short impulse type of signal it will spread out all over the spectrum - which is easier to "see" in frequency domain. Below plotted signal spectrum from 0 Hz to 19 kHz. The impulses/taps stand out can as orange lines on purple background. Amplitudes are scaled by colour - yellow (high)-orange-purple-black (low).

View attachment 179684
As it seems that Forum shrinks image-files, attached the spectrum plot also as PDF for better viewing.

[Amplitude plotted on linear scale, spectrum plot on mel scale]

---

What's the engine code - it's printed on configuration sticker under dash in driver's footwell.

It never ceases to amaze me the skills & knowledge of some people on here. Kudos

 

[Pedro20001]

Hi all, it's a 2021 with 25k , had it from 9k . Dealer said it will have to get worse before they can claim under warranty. I understand dealers are stuck in the middle but it still doesn't make it acceptable to me as the driver experiencing clutch judder albeit intermittently

 

[Simondo]

That noise along with clutch judder?. been there done that . Seems early at 25k but thats dual mass flywheel I reckon. Dealer surely knows that noise.

 

[Denisky]

Hi,
i have the same bad sound
with jolts in the clutch and more difficult gears to shift, a different sound when pushing the clutch pedal, the vehicle has had this problem since its 600 km.... and now 1100 km
it is going to the garage on January 11 to probably replace the flywheel.

 

[Denisky]

 

[david steven]

Hi Denisky

Have you managed to get your van sorted as I have the same issue… new flywheel and clutch and it’s back after 1000 miles. Mine is a 2021 with 19k on the clock had it from 5 k