Coupe GT ignition cut out problems

[Ed Kellock]

I had the same cutting out behavior with my 87.5 cgt many years ago. 
I don't recall ever noticing anything unusual with the tach, but mine
is digital so not sure how that might manifest itself.

Anyway, my problem turned out to be caused by battery acid getting
down in the wiring loom which was eating away at the wiring harness. 
Some time prior to this I had had a battery with a broken post and the
battery acid leaked down along the firewall and into the open end of
the wiring harness behind/below the battery tray.  The cutting out
happened well after the battery finally died and was replaced.

It got so bad I gave up and took it to a dealer who figured it out
quite by accident.  They had the engine idling while they were
removing the glove box to get at the ECU and when they moved some
stuff around under there, the engine stalled.

I was more than happy to pay the $400 they charged to clean and splice
in new sections of wire.  Afterwards, I even had all my console
illumination lights working; ones that I didn't even know existed.

Anyway, if you had a battery with a broken post that would be an
amazing coincidence, but I would imagine the same sort of damage could
be caused by water getting down in the same place.   No matter what
the cause, it sounds like flakey or corroded wiring somewhere.

Ed

On Fri, 2 Jul 2004 15:19:53 -0400, Chris Hall <bad_comrade at megsinet.net> wrote:
> 
> Problem:
> 
> 1985 Audi Coupe GT.  Engine has been stalling due to some sort of
> ignition cut-out.  Tach would drop straight to 0, as if a wire on the
> coil had been pulled / thermo switch had been disconnected / hall
> sender plug had been disconnected.  First time engine stalled, I
> popped the hood, disconnected the ISV's electrical connection, car
> started on the first try.  Figured "that must be it".  Reconnected it
> a week later (after flawless performance) and a day later, car stalled
> in same way.  Popped hood, disconnected ISV plug, started and ran fine
> for a while.
> 
> Then, while sitting at a light WITH the ISV unplugged, car stalled for
> the third time.  I played with all the plugs / wires you normally
> would, connected and disconnected the ISV a couple of times, got it
> started and drove fine the rest of the day.  Cleaned up the manifold
> ground wires, put new connectors on the black wires connected to the
> coil (because it laters seemed that unplugging them and reconnecting
> them got the car to start right back up...)  Car ran fine for a few
> days until I started getting the tach cutting out to 0 with a now NEW
> engine hesitation and occasional BACKFIRE.
> 
> Decided I'd try a new ignition module.  Got one for $10 off ebay, a
> new "Lucas" brand module.  Installed it today.  Car started right up
> and idled great (which it usually would do with the problem...).  Took
> the car on a test drive.  5 minutes in to driving, came to a stop and
> heard a slight engine hesitation.  Watched the Tach, and all the
> sudden, the tach started wildly fluctuating between 500 to 2000 rpm,
> even though the ENGINE WAS HOLDING AT A NORMAL RPM.  Then the engine
> idle started changing... going up to 1200 or so and holding, then
> dropping to almost dying (but catching itself) then up to another
> random RPM, etc.  NOT in a "dirty ISV" way, either.  Did this while
> the Tach needle was still doing it's own odd little dance.  Then at
> one point, I gave it gas and got NO response from the pedal, it
> started to mis-fire, and then died.  Couldn't get it to restart until
> the 4th or so try, and I drove home (couple blocks).  Parked the car
> and let it idle, and the engine RPM held steady, but the tach needle
> started "Dancing" a bit.
> 
> So, I ask... Can someone tell me with 100% certainty (like... you're a
> BOSCH TECH haha) WHAT SENDS THE TACH ITS SIGNAL?  I've always thought
> it was the COIL, but obviously the ICM is connected to the coil and
> the hall sender in the distributor.  ALSO, can someone tell me what
> relationship the ECU and the ICM have with one another?  (I didn't
> wanna "unwrap" the wiring to the ECU to look at the coloring unless I
> had to).
> 
> Again, the "dancing tach needle" problem is *NOT* the "dirty ISV" one,
> because it does so with NO change in engine idle, and this problem did
> NOT appear until I switched in the LUCAS ignition module.  Oddly
> enough, when I bought the module, the cross reference the guy gave me
> was the SAME 3 sets of 3 digits, but it was "missing" the LETTER at
> the end.  I asked the guy if this meant it wouldn't work, and he
> claimed that this Lucas module cross references to my car / module.
> 
> So I'm wondering if the new module is working properly, and has
> uncovered a secondary problem (maybe with the coil?) since the engine
> hasn't stalled with the tach going straight to 0 like it HAD BEEN...
> The few times that it HAS died since installing the LUCAS module, it's
> just kind of sputtered out...
> 
> I've been trying to figure this out for a month now (and the new
> problem for an hour or so), and although a few people have described
> the ignition cutting to 0 engine stalls, almost no one has posted how
> they fixed it (I'm assuming people talking about this a year ago
> aren't still dealing with the problem...)  One post on Audifans
> mentioned my exact situation with the ignition cutting out, and he
> said that he swapped the ICM and that worked.
> 
> The hose near the ISV is collapsed BUT "inflates" when you give the
> car gas... and HAS been this way for well over a year.  ALSO,
> sometimes when I pull the "spare" fuse for the ECU, the car doesn't
> run any worse with it pulled... although SOMETIMES the engine runs /
> fires like garbage with it pulled (which I'm assuming should happen
> EVERY Time).
> 
> Hope someone here can help diagnose what my old (and new) problem is...
> 
> Chris Hall
> "making girls cry since 1974"
> 
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