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VW B5 Passat TDIs This is a general discussion about B5 Passat(>98 (2004-2005 in North America)). Non TDI related postings will be moved or removed.

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Old January 22nd, 2019, 08:53   #16
mikko.rantalainen
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Join Date: Apr 2014
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Quote:
Originally Posted by imo000 View Post
Or sticking turbo vanes
I would guess the cause is sticking turbo vanes. Our old TDI Golf with AFN engine had sticking turbo vanes. I never put the turbo to pieces put it felt like the turbo vane ring had rust pieces or big sooth particles that caused it to move erratically. I had adjustable one way valve from boost pipe to turbo control vacuum pipe (T-fitting directly to the pipe that went to turbo). The idea is to configure to valve no not put any air unless the difference between the control pipe and the actual manifold pressure is too high (around 2.0-2.5 bar) and if that is exceeded the manifold pressure is leaked to control pipe to practically push the VNT mechanism closed (the push will obviously stop once the boost pressure drops to sensible values).

Before going with the valve I tried to manually move the turbo vanes back and forth every time the system seemed to have issues. The sticking does not always mean frozen in one position but just having problems with smooth operation. If you move the VNT mechanism manually over the full movement range for say 10 times and the movement is not smooth all the time you have sticking turbo vanes. The problem with the Audi/VW implementation in these cars is that the ECU will try to adjust the vacuum in the control pipe assuming that everything will work. The ECU does not know if the VNT mechanism moves at all, it does not know the rpm of the turbo. And still it tries to use vacuum solenoid to control the turbo rpm! The only feedback is has is the manifold pressure and there's pretty strict limits when it considers that the manifold pressure does not follow the assumed behavior (=everything works). The VNT mechanism does not need to be stuck for more than 0.5 seconds around 3500-4000 (engine) RPM and the ECU will enter limp home mode.

In our car, the colder it was outside, the more sticky the turbo got. I guess it was just thermal expansion in cast iron turbo housing causing already too small tolerances to get sticky.
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Old January 22nd, 2019, 09:01   #17
mikko.rantalainen
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Quote:
Originally Posted by mikko.rantalainen View Post
I had adjustable one way valve from boost pipe to turbo control vacuum pipe (T-fitting directly to the pipe that went to turbo). The idea is to configure to valve no not put any air unless the difference between the control pipe and the actual manifold pressure is too high (around 2.0-2.5 bar) and if that is exceeded the manifold pressure is leaked to control pipe to practically push the VNT mechanism closed (the push will obviously stop once the boost pressure drops to sensible values).
The thing was called Dawes TDI valve, similar to https://dawes-devices.com/products/d...ost-controller

Note that the valve is pretty hard to configure correctly. If you allow it to leak too much, you never get high boost and the acceleration will suffer (I never got limp mode so it's a start). If you set the limit too high, the device will do nothing. After I had used it for around half a year, I removed the device and the car seemed to continue to work nicely. I guess the device caused the VNT mechanism to move more than previously and it luckily cleared the particles that caused sticking. The car will be better without this kind of hack but it will help with the limp mode as long as the VNT mechanism is not totally frozen.

Be warned that this may cause turbo RPM to drop pretty rapidly once the valve opens which will cause drop in performance and some claim that it might be bad for the turbo bearing. I don't believe this to be bad for the turbo but performance drop is never a bonus...
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Old February 4th, 2019, 00:48   #18
kaneelschep
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Join Date: Nov 2017
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what about cleaning the turbo with mr muscle?
I see a lot of happy times about it.
https://www.youtube.com/watch?time_c...&v=56oIU-sF7d0
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Old February 10th, 2019, 23:11   #19
kaneelschep
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I really wanted to mr muscle this weekend, but then I had to find the hole in/and fix the fence cause the dog kept escaping to the street.
And sort all the cables in the living room, cause our little girl started walking.


I am definetely getting a can today.
Its so easily accessible in the b5 audi! Cant go wrong.
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