1983 Audi Coupe GT - Engine stalls on quick acceleration

[Ben Swann]

Oxygen Sensor. First,try unplugging it and seeing if that helps - you should see an
immediate improvement. IIf it has not been changed out in awhile, do it.  O2 sensor does
not come into play until system warms and goes into closed loop operation.

It could be something else throwing off your mixture - going lean on accel, but next
thing to try is O2 sensor - BTDT/seen it before many times.

If that is not it, suspect sticking air flow sensor plate.  Otherwise you have a major
air leak that you have not found yet.

Clogged fuel filter problem would happen at WOT.  You might be experiencing some sort of
fuel pump cut - the relay might be dropping out - you can bypass with a jumper or Orange
relay.  The pump itself may be loading up or failing, but your problem sounds to
consistant.  Relay the pump if you have not yet - will help save your wiring
harness/fusebox for when the pump does inevitably fail.

Don’t stick in any forks or thrown in a towel - you are close to finding the problem.
Everything else you did can only help.

Ben

[Date: Mon, 17 May 2010 17:07:22 -0400 (EDT)
From: AUDICPGT at aol.com
Subject: 1983 Audi Coupe GT - Engine stalls on quick acceleration
To: quattro at audifans.com
Message-ID: <334f6.2e168a48.39230a0a at aol.com>
Content-Type: text/plain; charset="US-ASCII"

1983 Audi Coupe GT 2.2L I-5  Miles = approx. 220K
 
What started out as a random issue has now become a constant problem... as
follows:
 
Engine starts fine cold, idles fine also.  Upon quick acceleration,  engine cuts-out, as
if complete loss of fuel pressure, ignition spark or  engine vacuum dropping the fuel
metering plate.  If I stay in the pedal,  the engine will die... if I jump off the pedal
and feather it, it will stay  running.  
On very easy acceleration, it will rev up normally to the  redline.
 
I checked all my vacuum lines for leaks - cracks - looseness, sprayed some  
starting fluid around connections... all seem fine, no spikes in idle.   
Removing oil filler cap does make engine die.
 
I suspected plugged up fuel filters since I have been there before on another vehicle of
mine.  I knew it had been at least 5 years,  so I replaced both filters, and also my
fuel pump that has been louder  as of late since everything was disconnected anyway. I
don't have a CIS fuel  pressure test kit, 
so I had no problem shot-gunning these replacements.   Also, while I had 
the filters disconnected, I checked the free-flow out of the  fuel tank... it was
strong, no obstructions there.
 
Testing upon reassembly = No change!
 
I was advised to replace my fuel distributor (it had been seeping), so I did w/ a
rebuilt unit from Python.
 
NO CHANGE!
 
I suspected stuck open fuel injectors causing fuel pressure drop in distributor... so,
since I had never had them cleaned I decided to take them in to Doctor Injector.  The
guy said that they were gunked up, but sprayed  fine now.  I was optimistic.
 
Reinstalled injectors (new seals too) = NO CHANGE!
 
I wanted to check and see what happens with spark during the event.  I hooked up my
timing light, find steady strobe on idle... rev'd up the engine slowly, strobe sped up
normally.  From idle, quickly opened the throttle, the strobe sped up, and when engine
cut-out the strobe continued to  pulse... 
SO, I surmised that the ignition system is NOT the  issue.  Spark is being generated at
time of stall.
 
 
I next considered waving the white flag and taking it to a shop  that had the proper
fuel system diag equipment I didn't have... BUT  FIRST...

 
Years ago, I had another car that the Cat convertor disintegrated & plugged up, creating
huge back pressure to the engine.  That car acted  similar to my GT's problem, and I
wondered if this was the case, it could be  causing back pressure that would affect the
fuel metering plate.  I  disconnected the exhaust to inspect the Cat... it looked fine,
I could easily  see right through it.  Discouraged, I decided to run open-header to
eliminate any questions about the entire exhaust system...
 
NO CHANGE!  Engine roared to life, idled fine, BUT cut-out on the snap accelerations!
 
At this point I've reached that PUT-A-FORK-IN-ME-I'M-DONE stage.  I  feel beaten (which
rarely happens to me with my vehicles).
 
I found this forum, and decided to give it a shot before limping it to the shop.  The
old GT has been a reliable commuter (keeping miles off my Infiniti G35 Coupe), so I can
only hope it is something simple I have overlooked, and not expensive as to be cost
prohibitive in fixing.
 
I thank you for withstanding my saga, and also for any ideas you may have for me.
 
Christopher]