Re-birth of my '90 200 tq

urq urq at
Mon Nov 23 11:26:23 PST 2009

I had an odd failure which created an overboost situation you may want to
check for ... 

On my car the line from the WGFV to the upper chamber of the wastegate was
done with doubled hose, that is the standard diameter line was run inside a
larger diameter fabric braided line; I assume it is some sort of a strain
relief.  Well, the larger diameter line ran up to but not on the wastegate
fitting, creating a stress point right at the fitting, causing the smaller
diameter line to get pinched right at the wastegate fitting.  

What this did was turn the area above the wastegate into a spring which
parallels the wastegate spring, making it stiffer, and thereby allowing
higher boost before the wastegate opens.  

It was a useful find for me as it greatly simplifies implementation of a
"Schrappnell Knobben" style boost enhancement mechanism.  The maximum
enhancement occurs by capping the upper wastegate chamber; if that gives too
much boost you can run a line some particular length with the end plugged.
If that is too much you can add a small chamber to the end of the line.
Since I already had the pressure regulator apparatus I never really had a
need to test further.  

Steve Buchholz

-----Original Message-----

Brian K. Ullrich wrote:

I do have a couple of issues with the driveability of the car. Two areas
concern me, and they are likely related.
First, the idle is a little rough once the car is warm, and it is prone to
stalling at idle then.


Have you checked your wastegate diaphragm? Sounds like you may be hitting
the overboost cutout, which is very violent. I am suspicious because you are
getting such high boost occasionally - the only time I have seen that
level is when my WFG diaphragm went.  The other telltale is if boost is
building very fast - it tends to (unfortunately) build la little more slowly
with the WGFV is working.

You can check by hooking a mity-vac to the WG diaphragm port.

90 200 QA
quattro mailing list

More information about the quattro mailing list