[urq] Re: Upper Wastegate Hose on '83 Ur Quattro

Brandon Rogers brogers at terrix.com
Thu May 6 11:26:58 EDT 2004

The boost pressure is regulated purely by pressure of the spring.  There is
no electronic control of boost, whatsoever.  I don't think it is possible on
WX for a vacuum leak to cause overboost, only "underboost" due to total lack
of electronic control.  If there is a leak in intake, it will bleed boost
off - and you should hear a hiss or whistle.  I guess there is a remote
possibility of a leak pre-turbo could cause some sort of overboost, but
personally I'd be surprised.  Is your wastegate cap modified so you can turn
down that screw? If so, maybe try backing the spring pressure off.  Yeah you
may want to check continuity of ATS wires to the ECU.  When mine were
properly soldered to the sensor, power was smoother through the rev range...


----- Original Message ----- 
From: "Ben Swann" <benswann at comcast.net>
To: "Steven. Buchholz (E-mail)" <Steven.Buchholz at kla-tencor.com>
Cc: <urq at audifans.com>
Sent: Thursday, May 06, 2004 7:44 AM
Subject: RE: [urq] Re: Upper Wastegate Hose on '83 Ur Quattro

[... are you still seeing 1.9 bar manifold pressure?  If so, that is
why your FP is shutting off.  I just checked the IST docs ... they indicate
that for any RPM at or above 2500, a pressure of 1.9 bar will shut off the
fuel pump.  At RPMs lower than 2500 the ECU will shut the FP off at even
lower pressures ... down to a minimum of a shade over 1.2 bar at 1000 RPM
and below.

Someone may have cranked down the adjustment on the WG spring perch ... but
I've got a pet theory I've never verified ... a theory that closes the loop
with your original report.  I am pretty sure that if you sealed that vent
line in the upper WG it would turn the air trapped in the upper WG chamber
into a parallel spring that would effectively stiffen the WG spring and
raise the max boost pressure.  Could that hose you have on the vent be
pinched by any chance?  I had a similar situation on a 5kT where the line
sealed the upper chamber and led to overboost shutdown triggers ...

Steve B
San José, Kaleefohnia (USA)
> Turns out, the overboost cutout, if that is what is happening is still
> there, just not as prevalent as before.]


This problem started happening after I did some minor service to fix an air
leak that I identified.  There is an o-ring seal around the bottom of the
IGLOO cover on the fuel distributor.  I repaired this air leak, as the
o-ring was broken.  I sealed with RTV fixing this air leak.  Car ran better
and started better, but then I noticed the cutout that I had not experienced

When I did the repairs, I had removed the turbo hoses, as I needed to
adjust/repair the idle switch too.  Everything is sealed tight now.

I read that the intake air sensor could cause this problem.

I think that I am still seeing 1.9 bar.  Wastegate diaphragm holds pressure.

I may still have an intake leak somewhere allowing the overboost.  I need to
understand how the boost gets regulated a little better, as it is a
different setup than the MC/5000 turbo which uses frequency valve to control
upper chamber and lower chamber pressures.

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