Advice needed; S6 engine problem

[Richard J. Andrews]

At 01:24 PM 4/30/01 -0500, you wrote:
get a fuel pressure gauge..
and run it with it connected and ziptied to the passenger side wiper blade..

this should help you see what exactly is going on..
possible it's a cat breaking up and plugging the exhaust?

HTH!
rich
'
>Okay, Guys...
>
>So I've got this "new to me" S6 avant, complete with RS2 turbo, manifold,
>injectors and an, as yet undetermined modded ECU (assuming MTM/Hoppen).
>Running smooth and strong for the first couple of weeks.  Then it starts
>intermittently "gagging" on itself.
>
>Pull up at a stop light and it's like it's missing on one or two cylinders,
>then crawling power only coming away from the light, which was luckily only
>two blocks down from the dealer, which is where I was headed for another
>reason.  Get my friend the service guy out and we repeatedly rev the engine
>and determine that it doesn't seem spark related, as it doesn't go away at
>higher revs, and are scratching our heads when it just disappears and
>smooths out.  Strange.
>
>Two days later, I'm headed home across the bridge.  Suddenly become aware of
>a strange resonance/vibration throughout the car, as if you're riding over
>soem bad stretch of road, but it can't be the road.  Try accelerating and
>realize, the engines crapped out again.  Downshift and try to rev it out; no
>go.  Proceed ahead (at the 9 mile mark on a 24 mile bridge) and realize that
>it's getting worse, but at least I'm still moving.  Nasty smell seems to be
>around.  Afraid I'm going to destroy the thing, but there aren't any real
>options at this point.  A guy in a pickup pulls alongside and motions me to
>roll down my window.  Says my car exhaust stinks to high hell, but it
>doesn't seem to be smoking.  Says it just started about a mile back. (No
>kidding!)  I continue like this for another 10 miles and...it just
>disappears again.  All smooth; full power.  Off the bridge and heading home
>on the backstreets.  A little over two miles away, here it is again...and
>then it's gone two blocks from my house, only to reappear as I pull into the
>driveway.  Unplugged the O2 sensor to check that and it was either unchanged
>or worse.  Sweet rich smell to start, immediately replaced with gagging
>sulphur fumes.  I'd had a pretty bad headache the last two days, so this
>could have been going on at a lower level for an extended time.  Normally, I
>don't get headaches.
>
>Having had a problem with water in the tank of the '85 urq recently, this
>possibility is also there.  Add dryer to the tank and try to drive it out
>again. No dice...until in sight of my house again and it's gone.  It was
>gone for the next three days until heading across the bridge this morning.
>It showed up five miles from the south shore.  However, this time I
>downshifted into fourth and brought the  revs up and then backed off a few
>times and it sputtered/spit and the problem was gone again.
>
>Been great weather lately.  Relatively dry for New Orleans and mid 70's to
>mid 80's.  Shell Premium in the car; filled up the day before this started,
>however.
>
>Any ideas or BTDT's?  Fuel, sensors, cats?
>
>TIA,
>
>Steve