[s-cars] Boost leak - update, what am I missing here?

[Mike Claire]

A bunch of you guys replied to me last week with ideas, and I appreciate the
help.  I've gone through everything suggested, and have read everything
about these issues I could find on Scott Mockrey's site,and STFA with
abandon.  I'm pretty much tapped - nothing to show for it.  I was distracted
this week by new symptoms - and ultimately #3 coil just failed entirely.
Dead short.  That's fixed now and the car runs great again - except it's
still low on boost.

(subject is a '93 S4, MTM 1+ (Pastore) chip.  Used to indicate 22 lbs on
A-pillar gauge.  Now it peaks at 16 or 17, and backs down from there.)

I'm either losing boost - or not making enough of it.  I don't know where
else to look - what am I missing here?

1.  Pressure tested main intake plenum to 15 lbs with a compressor and PVC
cleanout plugged into the intake boost.  Closed off Samco where it enters
the intake, and the ISV - PASSED

2.  Pressure tested all the small hoses in the PCV circuit, water trap, ECU
connection, boost gauge connection, etc. etc.  PASSED

3.  Removed BPV, plugged the Samco, plugged vacuum line (eliminate
possibility of BPV leaking pressure).   PASSED

4.  Removed silicone line from wastegate, plugged it shut (to test for
possibility of wastegate opening prematurely)  PASSED

I can only think of two possibilities - either the turbo is no longer
capable of building normal boost, or the intake plenum is leaking at
pressures higher than 15 lbs.

Could the turbo be failing?  It sounds the same and drives the same as ever


I can take the Samco off the turbo outlet and pressure test from there, but
I don't have compressor plug handy for that.


Before I do that - any ideas?


Mike