1.9 TDi, tech tip for freeing up VNT mechanism

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VAG Fan
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Location: Pretoria

1.9 TDi, tech tip for freeing up VNT mechanism

Post by VAG Fan »

This is a purely mechanical method for freeing up a VNT mechanism.

Disclaimers:
... this was done on a 2004 TDI, AHF engine; I can't say to which degree it applies to other TDIs
... "gentle force" may be subject to misinterpretation
... use at your own discretion.
[Edit, added 7/9/2018: this is really just a temporary fix. It doesn't address the root cause. Depending on the severity of the root cause, this fix would only last a few weeks to a couple of months. See today's post below.]

My overboost problem has been desribed here:
https://vwclub.co.za/forum/viewtopic.php?f=12&t=209015

When connecting and disconnecting VNT vacuum during idle, the lever on my VNT only moved about 3-4 mm. This should be more like 10-15 mm.

I was contemplating the oven cleaner method, but
... I couldn't get the exhaust off the turbo
... Stephan reminded me that the VNT mechanism sits behind the turbine, so chances for success are limited.

Rather, the idea is to gently pry open the VNT mechanism by working the lever to and fro. "Gentle force". Repeat: "gentle force".

I only had the car on ramps, so I was lying on my back while working on the actuator. I couldn't get a very close look, nor a very relaxed, controlled grip. So rather than disconnecting the actuator linkage, I left everything connected. I found that a 14 mm open-ended spanner fits on the VNT lever. With the engine off, I used this to gently pry open the range of motion of the lever. Then I started the engine and used the vacuum line to check how far the VNT would move. Repeat and rinse. In the end, I actually worked the spanner to and fro while the engine was idling (vacuum disconnected), to try and blow away some of the dirt. More repeat and rinse until I could feel proper mechanical end-stops in the movement, and until the vacuum and return spring could freely move the VNT through the whole range of motion.

Low vacuum = lever up = open vanes = low boost geometry for high revs ... this end of the motion range was completely fouled in my case.
High vacuum = lever down = closed vanes, high boost geometry for low revs.
Last edited by VAG Fan on Fri Sep 07, 2018 10:52 am, edited 1 time in total.
Mark R.
- - - - - - - - - -
2004 VW Golf TDI, type 1J, AHF, 317k (2016-current) --- daily
1990 VW Fox, type 16, HM, 304k (2005-current) --- spare runaround
Previous:
1992 Audi 500 SE, type C4, AAR (2001-2020) --- nice while it lasted
1983 VW Golf GTS, type 17, FR (1992-2005) --- most fun car I've ever had
1978 Audi 100 GLS 5E, type 43, WC (1991-92) --- died in the side of a Rekord who cut me off
- - - - - - - - - -
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WBN
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Membership No: 3056
Location: Durban

Re: 1.9 TDi, tech tip for freeing up VNT mechanism

Post by WBN »

Vag Fan....do you have a number I can personally contact you for regarding this ?
VAG Fan wrote:This is a purely mechanical method for freeing up a VNT mechanism.

Disclaimers:
... this was done on a 2004 TDI, AHF engine; I can't say to which degree it applies to other TDIs
... "gentle force" may be subject to misinterpretation
... use at your own discretion.

My overboost problem has been desribed here:
https://vwclub.co.za/forum/viewtopic.php?f=12&t=209015

When connecting and disconnecting VNT vacuum during idle, the lever on my VNT only moved about 3-4 mm. This should be more like 10-15 mm.

I was contemplating the oven cleaner method, but
... I couldn't get the exhaust off the turbo
... Stephan reminded me that the VNT mechanism sits behind the turbine, so chances for success are limited.

Rather, the idea is to gently pry open the VNT mechanism by working the lever to and fro. "Gentle force". Repeat: "gentle force".

I only had the car on ramps, so I was lying on my back while working on the actuator. I couldn't get a very close look, nor a very relaxed, controlled grip. So rather than disconnecting the actuator linkage, I left everything connected. I found that a 14 mm open-ended spanner fits on the VNT lever. With the engine off, I used this to gently pry open the range of motion of the lever. Then I started the engine and used the vacuum line to check how far the VNT would move. Repeat and rinse. In the end, I actually worked the spanner to and fro while the engine was idling (vacuum disconnected), to try and blow away some of the dirt. More repeat and rinse until I could feel proper mechanical end-stops in the movement, and until the vacuum and return spring could freely move the VNT through the whole range of motion.

Low vacuum = lever up = open vanes = low boost geometry for high revs ... this end of the motion range was completely fouled in my case.
High vacuum = lever down = closed vanes, high boost geometry for low revs.
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VAG Fan
Lieutenant
Posts: 1440
Registered for: 8 years
Location: Pretoria

Re: 1.9 TDi, tech tip for freeing up VNT mechanism

Post by VAG Fan »

I'll send you a PM.

But just to give some fair feedback, what I've described above is no permanent solution. The VNT mechanism keeps clogging up, and over time, it just becomes worse. I've done a couple of "treatments" since February, and at this stage, it only lasts couple of weeks, then the turbo goes back into overboost, causing limp mode. In fact, my "treatment" doesn't really free the mechanism any more, and the vacuum actuator can't move the VNT through the full range any more. Obviously the inside of the VNT is just completely filled with soot or tar.

After having read more on this issue, and consulting Stephan (panic-mechanic) and a few others, I realise that the proper repair is
1) to remove the turbo,
2) identify the root cause for the clogged VNT (either bad injectors causing soot, and/or oil leak in the turbo itself causing tar)
3) remedy this underlying problem
4) clean the VNT
5) reassemble.

Fortunately I already have a new turbo. So I can fit this and then fix the old one and/or attend to the injectors in due course.
Mark R.
- - - - - - - - - -
2004 VW Golf TDI, type 1J, AHF, 317k (2016-current) --- daily
1990 VW Fox, type 16, HM, 304k (2005-current) --- spare runaround
Previous:
1992 Audi 500 SE, type C4, AAR (2001-2020) --- nice while it lasted
1983 VW Golf GTS, type 17, FR (1992-2005) --- most fun car I've ever had
1978 Audi 100 GLS 5E, type 43, WC (1991-92) --- died in the side of a Rekord who cut me off
- - - - - - - - - -
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