Boost Level?

Phil Rose pjrose at
Wed Apr 3 16:48:10 EST 2002

At 7:06 PM -0500 4/3/02, Jobe Tichy wrote:
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>Quick question...This is the first turbo car I've owned and I have yet to
>reach full boost (1.8 Bar).  I can hit 1.6 consecutively and with no problems.
>I am curious to see what everyone else gets.

Everyone? Nah! There are far too many of us for that. Would you
settle for knowing what you _ought_ to get?

Check here http://www.SJMAutoTechnik.COM/20vboost.html for the full
lowdown on low boost problems.

While the Audi boost spec is 1.8 bar max, it's quite common--in  a
perfect, stock '91 200q--for the in-dash LCD gauge to show only 1.7
bar (although many people can get 1.8). But if you are getting just
1.6 bar using that dash gauge, it's probably indicative of some
problem. Of course it matters how you do the test for maximum boost.
Requires very rapid application of (full) throttle in a high gear
(4th) starting at about 2000 rpm and reaching max boost by 3000 rpm.
Might be best to try it on a very slight uphill grade.

The throttle switch must be functioning and adjusted properly so that
the ECU sees the wide-open throttle signal.
That (switch) is sometimes the cause for less than expected boost.

>   I know that elevation is a
>factor and I live at 2,000 feet so is this a major contributing factor?

Certainly can't be blamed on being at a measly 2000 ft.

>   I
>don't think I have a leak.

  But what about your car? :-)

>  I blew a hose on a urS4, so I know what it feels
>(and sounds) like to have absolutely no boost.  Could I have a small leak?

see above (YES)

>Any places to inspect for small leaks?

Hah! Check every places where you see a hose clamp on a hose that
_isn't_ filled with water.

The turbo bypass valve (TBV) is a place where a small leak can occur
internally, and that cannot be cured by simply tightening clamps. If
it's  leaking, then you must replace TBV. Also--the TBV is activated
by a small vac hose which comes from the back of the IM-- running
along the passenger side of the engine and tucked behind a heat
shield just above the exhaust manifold. That small hose will often be
well-toasted from engine heat; it often is cracked and creating a
leak that reduces boost and preventing operation of the TBV.

Another cause of sub-par boost is a malfunctioning "multifunction
thermoswitch" (MFTS). In fact, I'm presently waiting to for my engine
to cool off so I can replace the MFTS right now. It's the second one
in a month's time!!! However the failure of that switch typically
limits the boost to no more than 1.4 bar.


Phil Rose				Rochester, NY USA
'91 200q	(130 Kmiles, Lago blue)
'91 200q   (57 Kmiles, Tornado red)
	mailto:pjrose at

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