[s-cars] Ignition Problem?

[manuelsanchez at starpower.net]

S-heads,

I have been experiencing what I initially believed was an a
problem somwehere in the ignition system.  Patient is a 95.5
UrS6 Avant with 
-Bosch 3 Bar, Mihnea custom software north of the 20 psi mark
and RS2 like upgrades for that setup (injectors, turbo,
exhaust manifold), 
-Tom and Marc FMIC, 
-Samco hoses, 
-a relatively new WGFV (10,000 miles), 
-Forge 007 BPV, 
-5 Beru Coils (now have about 5,000 miles on them-soldered to
old wires after exiting the coil cover, new plug boots that
came with the new coils,
-original as far as I know POS's, 
-relatively new plugs (I have not checked them to see their
current condition though). 

Car has 118,000 miles on the odometer. I thought I had
replaced the fuel filter recently (within the last 18,000
miles, but I can't find the receipt.Original fuel pump as far
as I know.

I think it is a misfire that began first as a stumble.

It first occurred while at a driver school event this past
november.  The 2 variables just prior to it's first
occurrence, I filled up with 104 Octane leaded (at the time I
was running the test pipe sans kitties) and I pulled the
coilpack and laid it upside down on the fuel rail/intake to
check plugs for tightness after a run session.

What I originally felt at the track was an occassional
stumble, separated by a few seconds between stumbles, at
seemingly certain parts of the track. It was always at WOT.
What was strange is that in other parts of the course under
WOT I would not get this stumble.  I originally thought that
when I disturbed the wiring when I checked the plugs something
happened, an pinched wire, cracked insulation, who knows.  I
burned thru the tank of 104 and replaced with 100 unleaded and
then of course 93 since then, and the problem persisted on WOT
runs. 

Over the months the separation between stumbles has become
almost nil. I'll start a WOT run (the car is brought up to
normal operating temp first) I'll reach a few seconds of full
boost glory and then I'll get the misfire/stumble. If I back
off the throttle the stumble disappears. The stumble now is
more like a machine gun sound, a braaappppp, until I lift off
the throttle.

I have done the following:
swapped coilpacks with another car that was working, although
the other car was essentially running stock programming,
although I think the coils are on the older side

changed channels on my POS's - same problem

swapped both POS's with used units that were thought to be
good - same problem

Swapped ECU's - One out of Uncle Bob's Avant - same problem

The few codes that have come up are (sorry can't remeber
exactly at this moment what they are)

-some intermittent Oxygen sensor code (I had replaced the
Oxygen sensor with a oem unit about 10,000 miles ago and did
not have a problem back then) Occasionally while cruising with
about 0 boost the O2 light will come on for about 5 seconds
and then go off.

-only until recently, we have received the engine speed sensor
fault code (again can't remeber it exactly at this time), but
it was the "intermittent" signal code.  Codes I think have
always been checked with engine off, ignition on. I have read
some old posts in the archive that say you will always throw
this code if the engine is not running when you are checking
codes, but I don;t seem to remeber this code showing up in the
past, even with the engine off? 

Checked continuity in the spark plug boots they were all
within specs except one which was just a hair outside of spec.

This sensor is about $100USD.  I am reluctant to buy that
sensor since I have had this ignition problem in the past
without having that code thrown.  I am also looking at
possibly buying new POS's.

Someone has posted on Audiworld that they replaced both knock
sensors and their misfire problem went away.  Thoughts? Would
bad knock sensors throw a code?

I didn't think it was a fuel issue, but what do I know?

Any thoughts are appreciated, as I now have I week before the
next school and I would hate to cancel.

-manny
95.5 UrS6 still with stumble