Low boost/lack of power MC2-engine (MC dual knock)

[Andrew Dickinson]

I would not suspect a crack in the igloo myself.  The igloo is never
under boost pressure.  Unless it has been removed with little care,
leaned upon, or not reinstalled properly it is not likely to cause
issues in my experience.

Was there work done shortly before you noticed the issues?  Where is
your ECU located?  Is the vapor catcher cracked (in the line to the ECU
for pressure monitoring)?  Even a small leak can cause large issues.  I
agree that leaks in the pressurized part of the intake system can be
hard to find and cause hard to find problems.  BE systematic and careful
when checking.

Cheers;

Boxerfan

-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com]
On Behalf Of LL - NY
Sent: March 15, 2009 6:50 PM
To: Dag Bøsterud
Cc: quattro at audifans.com
Subject: Re: Low boost/lack of power MC2-engine (MC dual knock)

If boost builds to 1.0 bar (which is atmospheric) then quits, I'd
venture a
guess that you have a yet undiscovered system leak. Some of the less
obvious
ones (ask me how I know) would be the intercooler (yours is old enough,
they
leak along the end tank seams, and, unless you have the means to crimp
aluminum, it's not rebuildable), the lower intercooler hose (very well
hidden, and the only way to check it for leaks is to take it off
completely
and fully manipulate it, it's very heavy rubber) and the igloo over the
fuel
meter, which also needs complete removal and rather meticulous
inspection/manipulation to find leaks due to it's rather complicated
surfaces and hose connections. My former '89 MC2 had similar symptoms as
yours from time to time, and nearly every time it turned out to be a
boost
leak, although I was running 1.8 bar boost for a good part of the
"problem"
period.

HTH,

LL - NY

On Sun, Mar 15, 2009 at 5:25 PM, Dag Bøsterud <
dag.boesterud at consulgranada.net> wrote:

> I have a late 1990 Audi 100 TQ with the MC2-engine (also known as the
MC
> dual knock-engine).
> I have replaced all sensors including both knock sensor, the idle/full
> load-switch and the air filter.
> If I try to read fault codes, I get 4444 = no fault codes stored. I'm
quite
> sure I don't
> have any turboleaks or any major vacuumleaks.
>
> The car is in very good condition. The mileage is 131 000 miles. The
car is
> original, never had any
> modifications done to it in any way.
>
> The problem is that sometimes the turbo doesn't seem to boost at all,
or at
> least according to the
> gauge in the board computer. This occurs - if it occurs - after
driving for
> some time (30-60 minutes).
>
> Normally the gauge shows 1,4 at full boost, but when this occurs it
shows
> 1,0, and I can feel
> that the car feels more sluggish. Not that it is a monster when it
boosts
> 1,4 (0,4 bars), but when it
> supposedly doesn't boost at all? I'm sure it boosts something, but
it's not
> a lot..
>
> What could cause this?
>
> /Dag
> Norway
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