No start, no spark - 1987 5KS with NF engine

[Dave C]

 <200q20v at audifans.com>
Folks,

I'm about at the end of my rope in trying to find the cause of this no
start, no spark problem. This car is a 1987 5KS with NF engine and CIS E-III

The car always ran fine and then began to act up about a few weeks ago...
failed to start once or twice, but later would start and run as normal. Shut
it off and maybe it would start again, maybe not. Now for the past couple
weeks I haven't been able to get it to start at all. I checked for fault
codes several times and got none ... just 4444. The battery has lots of
juice and the starter cranks the engine nice and fast.

There is no spark from the coil. I tried various tests as described in
Bentley ... coil, power stage (ignition booster?), and a few other things. I
swapped various parts including:

Knock sensor control unit (aka ICU, aka electronic ignition control unit) in
drivers side footwell

ECU (fuel injection control unit)- in the passenger footwell

Coil incl power stage (ignition booster)

Distributor ... although I don't think that has anything to do with lack of
spark at the coil

I checked the grounds in the engine compartment, all looked OK, cleaned them
up anyway.

Checked all wiring connectors at coil, distributor, etc

Examined all related wiring that I can see/identify for obvious signs of
damage ... all looks OK.

Bentley's test of the ignition coil seems to indicate either a bad ICU, or
damaged wiring to the ICU. I checked for continuity in the wire between the
coil and the ICU and it's OK. I swapped the ICU with another one out of a
car that runs fine and the car still won't start.

The only remaining thing I can think of is a broken/damaged wire somewhere,
maybe inside the harness. But where to look?
I'm very close to giving up and having it towed to an Audi specialist.
Admittedly, I'm not a pro ... it's possible I'm not doing the tests
correctly, and my wire diagram skills are not the greatest.
Does anyone have a suggestion re: what I might have missed? A likely
location for a damaged wire? Anything at all?
thanks,

David Conner

Columbus,OH
87 5KTQ
89 100 NF engine
87 5KS NF engine