RE: '98 A6 2.8 won't start- mechanics are at a loss...

["Paul Wilson" <pauldwilson@ne.mediaone.net>]

> I've never heard of carbon build-up in a properly set up Audi engine.

Supposedly, newer Audis do have problems with carbon buildup.

I recently put an APR chip in my A4 1.8TQ.  The car really takes off but I
can feel the knock sensor kicking in if I floor it.  According to APR this
is due to carbon deposits which the 1.8T has a real problem with.

Does anyone know how to do a service to eliminate the deposits?  Supposedly
if I get the right nasty chemical, I can spray it in either the air intake
or a vacuum line to the intake manifold and this will dissolve the deposits.

I'm going to try some stuff in the tank first.

> Supposing the phenomenon to exist, however, I find it vanishingly
> unlikely that all five cylinders would simultaneously be affected by
> lumps of carbon holding the valves open.  And even less likely that the
> car would pass any kind of compression or leakdown test in this state.
>
> Tom related a story about a car suddenly stopping on the highway and
> passing compression tests.  I suspect, in fact, that it actually passed
> _leakdown_ tests.  The key clue is the high engine revs on the starter.
>
> The condition is documented in the 20V (RR) manuals and the primary
> cause is given as incorrect assembly of the oil pressure relief valve.
> Obviously this isn't the cause if it happens out on the street - you
> have to postulate some other reason for relief valve failure, like a
> piece of crud or a broken spring.