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

[LL - NY]

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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