strange noise when engine turned off

[mixskoda]

As the title says, when I turn off my engine it has now developed a strange groaning sound that starts about 10 seconds after you turn it off and lasts about the same. It still runs fine its just that it never used to do it so was wondering if something is on its way out ??

[Stu vRS]

Throttle body alignment noise maybe - if it is, this is normal.

[nick74]

It's very likely the EGR solenoid located within the black vacuum control block mounted on the bulkhead that is resonating as the vacuum pressure drops after engine shutdown and causing the noise.

 

http://www.ebay.co.uk/itm/GENUINE-VW-VOLKSWAGEN-SOLENOID-VALVE-BLOCK-6Q0906625E-/331149455243?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item4d1a0baf8b

 

Mine always did this, I tried cleaning it with compressed air, killed it completely, and had to spend £193 on a new control block.

At least with the new control block fitted the groaning noise stopped totally!

 

If I were you I'd either try and get a decent used replacement, or just live with the groaning noise (unless you've got £193.99 burning a hole in your pocket).

On mine the noise never caused any other issues in 4+ years, it was always louder in winter for some reason, and after spending all that money just to cure a noise I wished I'd just left it alone to be honest.

[mixskoda]

^{Thanks for that. Will I be causing any harm if I just ignore it ?}

[nick74]

No, no harm at all. I suspect if I'd left mine it would have gone on for years happily groaning/farting every time I turned off the engine. I only investigated it as the noise started to get quite embarrassing!!

Even if the solenoid valve failed completely it would just bring up the engine management warning light with a fault code for insufficient EGR flow (which is what mine did after I'd killed the valve trying to clean it.) The car would still drive normally.

[adfabia1]

Tandem pump leak?

[nick74]

Well, it definitely wasn't on mine. Replacing the vac control block silenced the noise for good. It seems fairly common for them to make this noise but it doesn't appear to mean impending failure.

A way of proving it one way or the other would be to unplug the electrical connector from the back of the unit and run the engine for a few seconds. When switching off the engine it should now be silent as none of the vacuum solenoids will have opened. Bear in mind though that doing this will very likely cause fault codes to be stored in the ecu.

[mixskoda]

_{Just took a picture of the noisy culprit under the bonnet and it seems to fit your description.}

[tamiyaandy]

Mine does this aswell, as people say it does not cause any issues so I just ignore it, sounds like a cow going Moooo from a distance!  LOL.

[nick74]

_{Just took a picture of the noisy culprit under the bonnet and it seems to fit your description.}

 

Yes, that's the one.

[Mando1214]

Mine does exactly the same noise, thanks everyone as i was getting worried about this too!

[nick74]

Mine does this aswell, as people say it does not cause any issues so I just ignore it, sounds like a cow going Moooo from a distance!  LOL.

 

Mine started as a distant mooing and over the years built up to sound like a nearby flatulent bull. On one occasion it caused a passing dog to turn and start barking at the car!

[tamiyaandy]

I have both of the well documented noises under my bonnet, The Moo Cow as we have discussed from the black vac box thingy, and I get the kinda fake dump valve / air release noise when I lift of the throttle / change gear.

 

One could say its almost orchestral under my bonnet!!

[Phil-E]

I have both of the well documented noises under my bonnet, The Moo Cow as we have discussed from the black vac box thingy, and I get the kinda fake dump valve / air release noise when I lift of the throttle / change gear.

 

One could say its almost orchestral under my bonnet!!

 

Is the turbo/dump valve kind of noise quite faint?

 

I get a similar noise although I never hear it while driving normally as the gear changes are so quick. I hear it more when sat still revving the engine in neutral.

 

Phil

[tamiyaandy]

Hi Phil, All depends if I try and "force" the noise, I.E if I accelerate hard but low down to produce the boost quickly ( Say 1200-1800 rpm in second ) then just lift off its loud enough to be heard inside with the Radio off.

 

But if I accelerate through to a normal gear change, Say 2200-2500 rpm then it wont do it.

 

But with the drivers window down, Low revs, Full boost, And snap the throttle shut, Its very clear kind of Fluttering air sound, as I say its like a quiet dump valve on a wastegated Engine.

 

no one seems to offer a clear answer why a VNT Turbo makes the noise.

[mixskoda]

Is this the turbo or the alternator slowing down again after the sudden deceleration of the engine and the alternator clutch pulley doing its thing ? Just a thought.

[tamiyaandy]

A good thought Mixskoda, But you can clearly hear its an air release so cant be the alternator, and at that point the engine is not decelerating as you have only just closed the throttle. 

 

Its clear its the excess boost that's been built up and has to go somewhere, I guess my question is, on a normal Fixed turbo with wastegate we know were the excess pressure goes ( The wastegate )

 

But on a VNT turbo there is no wastegate, pressure is regulated via the variable vanes, so when there is an excess of pressure how does it git rid of it? , Via the EGR system ? ?

[nick74]

A good thought Mixskoda, But you can clearly hear its an air release so cant be the alternator, and at that point the engine is not decelerating as you have only just closed the throttle. 

 

Its clear its the excess boost that's been built up and has to go somewhere, I guess my question is, on a normal Fixed turbo with wastegate we know were the excess pressure goes ( The wastegate )

 

But on a VNT turbo there is no wastegate, pressure is regulated via the variable vanes, so when there is an excess of pressure how does it git rid of it? , Via the EGR system ? ?

 

The idea of a VNT turbo is that there is no excess boost in the first place, the vanes of the turbo are constantly varied to provide exactly the correct amount of boost according to engine load, speed. If the vanes stick for any reason (eg accumulated carbon on the mechanism) and too much boost is generated the ECU immediately reduces fuelling to reduce the engine speed, i.e limp home mode.

 

I think the sound VNTs make on gear changes etc is probably caused by the changing position of the turbo vanes as the engine revs drop.

[tamiyaandy]

Nice clear answer there Nick, And your analysis sounds spot on, I think its the vanes closing back down flush after being fully extended to maximise the surface area within the impellor forcing the compressed air inside out.

[Dk21]

On 13/12/2014 at 16:16, nick74 said:

Well, it definitely wasn't on mine. Replacing the vac control block silenced the noise for good. It seems fairly common for them to make this noise but it doesn't appear to mean impending failure.

A way of proving it one way or the other would be to unplug the electrical connector from the back of the unit and run the engine for a few seconds. When switching off the engine it should now be silent as none of the vacuum solenoids will have opened. Bear in mind though that doing this will very likely cause fault codes to be stored in the ecu.

Hey nick! Buddy i just got cleaned my skoda laura egr valve cleaned after dismantling.. But no issue with pickup only creating a vaccum leaking sound when i deaccelerate it from arnd 2500rpm.Intake hose also getting puffy on accelerating high

Please suggest 

[nick74]

On 17/06/2019 at 14:17, Dk21 said:

Hey nick! Buddy i just got cleaned my skoda laura egr valve cleaned after dismantling.. But no issue with pickup only creating a vaccum leaking sound when i deaccelerate it from arnd 2500rpm.Intake hose also getting puffy on accelerating high

Please suggest 

Hey! 

I hardly visit this forum now as I sold my Octavia in 2014, but I got an email saying someone had quoted my post. 

Your problem sounds odd, particularly the intake hose getting puffy on acceleration. I wonder if you have a partially blocked intercooler? Or Perhaps the anti shudder flap is sticking partly closed? 

Edited 18 June, 2019 by nick74