I have an '85 760 turbo that is having a problem with the turbo system.
Whenever the gauge goes into the boost mode, you can hear a whistling noise
that gets louder with increased boost.  It is pretty obvious the turbo is
spinning up and providing boost.   The gauge shows plenty of boost--almost
goes up the red, but stays in the high yellow (ok boost) zone.  When it is
in this mode, the engine is running very rich, pouring out lots of black
(gasoline) smoke.  And when this is happening, the car can't get out of its
own way!  Drive it very lightly and it runs OK.  The problem has been
getting progressively worse over the last several months.

What I am pretty sure is happening is that there is a major leak somewhere
in the compressor output (boost) side--the turbo runs up, moves plenty of
air, the mass airflow sensor thinks it is really putting lots of air into
the engine, so it delivers the appropriate large amount of fuel.  Problem
is, the engine isn't getting the air--it is leaking out.

My problem is that I cannot find where such a leak is!!  I've tried soaping
down the entire boost side of the turbo system and putting it into its
failure mode, but did not see any bubbles, though I had to run it and look
when I stopped.  I also removed the intercooler and pressurized it with my
shop vac while soaking it with soapy water--still no symptoms.  The
intercooler had several tablespoons of oil which would indicate some
compressor seal leakage, but I think it has been some time since it was
drained.  I've checked all hoses, etc.--No signs of tears, leaks, or
looseness.

Any ideas?  Has anyone encountered this problem in the past?

Thanks in advance.
Lew Barton