Motoring Discussion > Carbonisation of VVT Miscellaneous
Thread Author: Rudedog Replies: 17
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 Sun 2 Feb 14 09:35 
 Carbonisation of VVT - Rudedog
I've had a search on the net and can't find anything on the subject.

I'm not talking about the turbo bearings but the black crud that adheres to the vanes and can stop the variable vanes working properly, I guess as it's using exhaust gases that it must be something in that, and if so is there anyway of reducing the build up?
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 Sun 2 Feb 14 10:13 
 Carbonisation of VVT - madf
I take t this is A VW turbo?

If so a common fault...
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 Sun 2 Feb 14 10:35 
 Carbonisation of VVT - NortonES2
This? tinyurl.com/ofpgqfj
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 Sun 2 Feb 14 20:41 
 Carbonisation of VVT - Rudedog
Thanks to both of you. Yes I've had three episodes of overboost resulting in limp-mode (Golf GT TDi). I was just wondering what causes it? Once it's fixed how can I try and prevent it happening again, I've always run it on good diesel (I know some people don't think it makes a difference).
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 Sun 2 Feb 14 21:10 
 Carbonisation of VVT - Mikhail Ribbendik
You could always do some research on a product like:

www.forteuk.co.uk/product.php?id=62/Diesel_Turbo_Cleaner

to see if it's worth throwing any money at.
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 Sun 2 Feb 14 22:03 
 Carbonisation of VVT - Rudedog
I'm guessing you add this to the diesel? I still would like to know what causes it, is it the hot soot in the exhaust gases and if so don't all of these additives just try and improve the burning power of the diesel.
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 Mon 3 Feb 14 11:16 
 Carbonisation of VVT - DP
Low quality (supermarket?) diesel is implicated. As is not "exercising" the VNT mechanism frequently enough. Gently driven cars that are ambled around town suffer much more than those driven harder.

Flooring the throttle from 1500 RPM right round to 4k will ensure the VNT mechanism cycles through its entire range of movement.

Ours is run on decent fuel, and gets regular exercise. We have not seen the issue yet (touch wood).

Internet folklore suggests that a can of strategically directed Mr. Muscle oven cleaner is all that is needed to "unstick" the mechanism and restore normal operation. A dealer will replace the turbocharger, which is completely unnecessary.
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 Mon 3 Feb 14 11:26 
 Carbonisation of VVT - NortonES2
"Low quality (supermarket?) diesel is implicated. As is not "exercising" the VNT mechanism frequently enough"

That's my impression too DP. A while since I had a VAG diesel, but I took into account some advice from Fred's TDI site, on the need for VNT exercise. They suffer (or did) more from low fuel quality over there. Thus the advice to do the "Italian tune-up". There were a couple of places on the M58 and M6 where I could give fully welly in third, on a warm engine, up to and beyond 4000 rpm! The Audi ran to 70k as did the following Passat before I changed, with no hiccups.
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 Mon 3 Feb 14 11:30 
 Carbonisation of VVT - Mapmaker
>>The Audi ran to 70k as did the following Passat before I changed

You had barely run them in!
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 Mon 3 Feb 14 13:30 
 Carbonisation of VVT - NortonES2
Exactly. Cam belt change looming: policy to get rid before hamfists get to work.
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 Mon 3 Feb 14 14:15 
 Carbonisation of VVT - DP
>> Exactly. Cam belt change looming: policy to get rid before hamfists get to work.

Ours is due a belt in 5,000 miles. No immediate plans to move the car on, so we will get the water pump done at the same time as is recommended on these engines.

The camshaft drive on the ASZ variant of the PD fitted to the Golf is very well engineered, and the VW tech who has serviced the car for the last 5 years reckons that belt failure on these engines is "almost unheard of*"

*typed with a large pinch of salt :-)
Last edited by: DP on Mon 3 Feb 14 at 14:16
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 Mon 3 Feb 14 22:29 
 Carbonisation of VVT - Rudedog
Well I always feed mine on a diet of Shell or BP and I did try and give it full throttle on many an occasion but believe me even with only 140PS I was very quickly nudging three figures. I've now spent the money on getting the turbo fixed, I was at the point of changing cars but I really wanted a GTD and I just couldn't find one with the options I have on my present car for less than 20K.
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 Tue 4 Feb 14 08:34 
 Carbonisation of VVT - Old Navy
>> ......... but believe me even with only 140PS I was very quickly nudging three figures>>

Try a lower gear. The plan is to use the full rev range, not to go fast. :-)
Last edited by: Uncle Albert on Tue 4 Feb 14 at 08:35
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 Tue 4 Feb 14 12:15 
 Carbonisation of VVT - Rudedog
Message understood, I'll flick it across to manual and hold it in third for as long as I can, just got to find a suitable road otherwise I'll have the same issue, it does have a lot of mid-range punch which very quickly winds the speed up.
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 Tue 4 Feb 14 12:43 
 Carbonisation of VVT - RichardW
What you need is load not speed. It will have spooled up to full boost above about 2.5k rpm as long as you are working it hard - ie climbing a hill in 2nd or 3rd.

The soot is an inevitable part of the diesel combustion process. You can't really avoid it. Minimise by decent diesel, working it hard occasionally to help burn it off, and getting anything that causes it to smoke (eg EGR valve) fixed. Soot reduction technology (ie particle filters) are downstream of the turbo.
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 Tue 4 Feb 14 15:19 
 Carbonisation of VVT - Old Navy
>> What you need is load not speed. It will have spooled up to full boost
>> above about 2.5k rpm as long as you are working it hard - ie climbing
>> a hill in 2nd or 3rd.
>>

Agreed, A better explanation than mine, A long uphill motorway slip road is good, but as Scotland is a bit undulating with the odd one or three mountains it is not a problem loading an engine, and they thrive on it.
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 Tue 4 Feb 14 15:28 
 Carbonisation of VVT - Rudedog
Strange thing is that a I've never really suffered from a smokey exhaust even under hard acceleration, the EGR valve was deemed to be OK as part of the health-check before the turbo was changed.
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 Tue 4 Feb 14 15:35 
 Carbonisation of VVT - DP
'Italian tune ups' are good for diesels.

Thanks to serious roadworks en-route, the 320d is spending a heck of a lot of time ambling along at walking pace since Christmas. 20 mile commute now taking anything up to 90 mins which says it all. I took a solo run up to Oxford at the weekend on near empty roads, and gave it a proper pasting. Plenty of full chat acceleration up towards the redline, and a sustained cruise on the motorway at "making progress" speeds.

The difference in responsiveness and general smoothness before and after this treatment is marked. SWMBO drove the car today for the first time in about a week and commented on it.
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