Wastegate, how does it work?

[Peter Berrevoets]

Don't touch the wastegate, it isn't likely to be faulty. If the wastegate
fails, it is a broken diaphram causing overboost all the time.

Under boost is generally ECU/ignition system related (sensors, wiring, fault
conditions), or faulty hoses.

The big hose to the wastegate and the intercooler itself are my bet on the
sources of your problems. The big hose died first (a long time ago) and an
overboost cracked the intercooler end cap(s) loose. You may never have
noticed because the overboost may have resulted from a pressure spike at
throttle closure.

HTH

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



> >-----Original Message-----
> >From: Smeins, Larry [mailto:lsmeins at ball.com]
> >Sent: Tuesday, February 20, 2001 12:30 PM
> >To: 'Peter Berrevoets'
> >Subject: RE: Wastegate, how does it work?
> >
> >
> >Peter,
> >Thanks for the tips.  The Michelin man hose has been checked
> >many times.  I
> >haven't checked the intercooler but discounted that
> >possibility because the
> >car has never exceeded 1.3 bar at full throttle as long as
> >I've owned it,
> >over 210k miles and 10 years, so the 1.6 bar at 3/4 throttle
> >was indicative
> >of something drastic happening.  I will check it.  The
> >manifold to wastegate
> >hose hasn't been checked recently and I will do that, too.
> >
> >My questions were directed at use in trouble shooting to
> >determine if the
> >wastegate was functioning properly or not before ripping it apart.
> >
> >Thanks again,
> >
> >Larry
> >
> >> -----Original Message-----
> >> From:	Peter Berrevoets [SMTP:pjberr at home.com]
> >> Sent:	Tuesday, February 20, 2001 9:55 AM
> >> To:	'Smeins, Larry'
> >> Cc:	1 Quattro List (E-mail)
> >> Subject:	RE: Wastegate, how does it work?
> >>
> >> 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
> >> > >