Wastegate, how does it work?

[Peter Berrevoets]

I detect a big leak in your high pressure side intake. The Michelin Man hose
is not likely the ciulprit because once gone if won't heal itself to give
you that overboost condition. I would check all hoses and clamps from the
turbo to intercooler, check the intercooler for separation of end caps (or a
crack that could have frozen over) as well as the big line that comes from
the intake manifold to the bottom of the wastegate.

I think you will find two problems;

1) that last line is shot

2) either you have a loose clamp or the intercooler end caps are not sealing
anymore under pressure

HTH

Peter Berrevoets
1990 200TQ
Toronto, Canada
http://frontpage.home.net/pjberr/



> >-----Original Message-----
> >From: quattro-admin at audifans.com
> >[mailto:quattro-admin at audifans.com]On
> >Behalf Of Smeins, Larry
> >Sent: Tuesday, February 20, 2001 10:46 AM
> >To: 'Audi'
> >Subject: Wastegate, how does it work?
> >
> >
> >My 87 5kcst has been suffering from low boost for a long
> >time.  I've gone
> >over the boost trouble shooting items on the web page
> >addressing boost to no
> >avail.  I even spent several hundred at the dealer and the
> >best they could
> >do was get the boost to 1.2 bar at 6000 RPM and that
> >improvement soon went
> >away.  Even with low boost, presently 1 bar at 5000 ft
> >altitude, the car
> >runs fine so I have been living with it.  I've always been
> >suspicious of the
> >wastegate or its control but haven't dug into that item,
> >yet.  A couple
> >weeks ago, on a very cold morning, I think the wastegate
> >stuck shut.  I left
> >my drive and as I pulled into traffic I gave it about 3/4
> >throttle and to my
> >amazement I felt my self being pressed back into the seat
> >like I'd never
> >experienced before in my Audi.  I looked at the instrument
> >panel boost
> >display and saw 1.6 bar at which point the engine cut out a
> >bit and recaught
> >again at 1.5 bar.  I think it was hitting the overpressure
> >cut out.  A few
> >miles down the road I turned a corner and when I pressed the
> >accelerator in
> >my normal fashion the front tires broke loose.  Wow, I guess
> >I'd forgotten
> >what these 5k turbos could do.  After the car fully warmed
> >up the boost
> >dropped back down to 1 bar max and is staying there again.
> >I think its time
> >to look into the wastegate, so, some questions.
> >
> >I believe the wastegate is controlled by a combination of
> >mechanical spring,
> >manifold vacuum/pressure, and pulse width modulated
> >electrical.  How do
> >these inter-relate?
> >
> >If I remove the vacuum line what will happen to the
> >wastegate operation.
> >Will it default open, close and become purely mechanical, or
> >something else.
> >
> >The same question for the electrical control.
> >
> >Is there some way to block the wastegate closed to verify
> >that my boost is
> >being limited by wastegate opening?
> >
> >Any other trouble shooting tips?
> >
> >Thanks for any help you can offer.
> >
> >Larry
> >