[urq] More Weird UrQ Behavior

[urq]

... you can leave the car with me for a few years and I'll get to the bottom
of the problem for you!  :-)

The good thing about newer motors is that they detect most operational
problems; to my mind the fact that you aren't getting any codes is telling.
I suspect some sort of fuel delivery problem.  How much fuel is in the tank
when the cut out occurs?  Does there seem to be any correlation between the
amount of fuel you have and the cut out?  

I was thinking about ways you could check for the lack of fuel, and was
thinking a pressure gauge on the fuel rail would help ... you'd have to
figure out how to plumb it in, and then find a place you could drive the car
to test.  That is why I was thinking it might be interesting to run a test
on a dyno to see if you can repeat the condition.  I don't know how
expensive the dyno time would be, but it would allow you to instrument
things like fuel pressure and watch it during the run.

I've always wondered why Audi switched to pumps inside the tanks in the
mid-80's, and suspected that it was to provide pressurized fuel from the
tank and not depend on the suction through the feed hose from the tank.
I've read from a couple folks that cavitation in the feed line to the
external pump becomes problematic at higher power.  You may have another
reason to find a way to fit that A8 fuel tank into the trunk somehow after
all!  :-)

Good luck Andrew!
Steve Buchholz

-----Original Message-----

So, at the past 2 track events I've attended with my V8 UrQ I have had a
weird issue with engine cutout at high rpms, usually in 3rd gear, but on the
straightaways in 4th gear. They seem to occur during any throttle position,
like cresting a hill, or accelerating out of a corner, which is somewhat
unnerving. There are no fault codes thrown at all, which makes me think it's
a fuel supply issue. Here's the weird thing, I would say it a fuel pump
relay issue, but wouldn't the engine stall (that's what my old UrQ and Coupe
GT would do on the highway), but in this case there's no power until I
depress the clutch after slowing a little and downshifting, then the power
is all back. The engine never stalls and shuts off! I confirmed it's not a
rev limiter issue by redlining with moderate throttle input and no issues
occured. It's definitely at higher RPM though. Does anyone have a thought? I
thought about relaying the fuel pump, but wouldn't the engine simply stall
with no fuel supply, or will it simply keep running with the car in motion
and clutch out without shutting down or turning on all the warning lights on
the dash?

Any help is appreciated. Thanks.

Andrew Finney
1985 UrQ 4.2L ABZ