speedshopmike

oh, PS:
like any transistor, injector drivers have a finite lifespan, esp if audi uses low impedance squirters.
seen scores of failed ecm's in my time; it's definitely possible.
be sure to meter that suspect injector; it could have been the root of a driver failure.

bjwhite

If by meter you mean check resistance across leads, then it's in spec...I got an exact reading to the published spec which I seem to remember is 12.1 ohm. I did that rather early on in the diagnostic...but yeah, I do agree that it could have been the root cause if faulty.

klimnick

I had the same problem with my 06 s4 with cylinder 2 misfire. I did change everything I could to fix it but no success. I checked last thing what came to my mine. I did compression test on catalytics and one of them was bad. Try to remove first o2 sensor from the engine and check compression with the same tool you used for cylinders. if it is more than 5psi on running car, it means it's bad. My one had 25psi and another 5psi. I changed the passenger side cat and my baby fly's again like before. I think you need to check driver's side. Good Luck I hope it will help you.

bjwhite

Really? Your #2 injector didn't fire because of your catalytic converter having slightly less flow?

klimnick

Yes, Sir!
I couldn't believe in it too but it helped in my case there was big difference in PSI between two cats.

bjwhite

No, I'm saying...did you actually test using a noid light on your #2 injector or were you just ASSUMING due to your #2 misfire findings. In my case, I get no pulse to #8...but I get fine pulse to #7--regardless of cat compression. See what I mean?

bjwhite

Hmmm...doesn't seem like the plug or the wiring. Testing the signal wire to pin 89 on the ECU...that looks fine. Then tested the black/blue wire (ground) to ground and also tested fine. Then hooked everything back up and still get pulse on Cylinder 7 but nothing on Cylinder 8.

So.....it's looking like a failed ECU oddly enough. And, I also read that only the dealer can do that work. Grrr......so annoying these "security" features on modern cars.

Unless anyone else has an additional idea...it's looking ECU related.

speedshopmike

this forum is basically a desert and i'm not audi proficient enough to offer anything further (i'm a domestic car guy).
you should seek out "jimmybones" on audizine/quattroworld/audirevolution if you need further tech advice.
he's a factory tech, knows his ****, nice & helpful guy.
those other forums have threads about the "good" independent audi shops in a given area; do some searching and you should be able to avoid the dealer.
good luck

bjwhite

Wow guys....what an adventure. So this absolutely turned out to be a failed ECU not firing the #8 fuel injector. I sourced a used ECU from a 2005 S4 (same part number as mine actually) and it's now all coded and matched and the car runs beautifully just as before. So...it was not the timing guides or a failed coil. It was not a clogged injector or a bent valve/no compression. Simply put, there was no injector pulse on injector #8 coming from the computer off pin 89 in the connector--so the injector driver (transistor I think) in the old ECU failed dead--as suspected in the diagnostics. We were spot on.

First off, thanks to all who offered advice and thoughts during the diag process.

Thanks to SpeedshopMike for initially pointing me in the direction that this could be the injector driver in the ECU itself. That thought it what sent me down the path of actually testing out the injector pulse with a noid light and sent me to the solution here.

Thanks to JimmyJones on AudiZine for many pieces of input during the diagnostic and troubleshooting process.

Thanks to my buddy Jason Harris who #1 sold me the car 3+ years ago and has loaned me his VAG-COM a few times during my ownership.

And last but not least, my god....SPECIAL thanks goes to Daz Dillenger on AudiZine. What an amazing guy who went out of way on MULTIPLE occasions to help me out. #1, out of the blue when reading this he was so kind to share with me the ECU pin outs (that I could not find elsewhere on the internet). That allowed me to do a wiring harness continuity test into the ECU connector to prove out that this was not connector or harness related. Then on top of that, worked to help find a replacement ECU.

THEN....and this was the CRAZY thing. When I sourced a replacement ECU locally, he jumped online with me on practically a moment's notice to help code the ECU to the car. I am in Seattle so I was on Pacific time and it was pretty late when he replied to the email. He still was unbelievably kind to jump on, even though it was closing in on 2am his time, to code the ECU so my wife could have her car back for this weekend. (She's going to a ski race about 6 hours away).

Thank you so much Daz....I appreciate your help.