vortexblue

Our A6 has been acting up, it's now a non-starter; here's the details:

*very intermittent stumbling and rough engine under throttle or idle. Brief flashing CEL and misfire code 16687-- cylinder 3.

-I changed the plugs with factory NGK's and it came back a few days later. I swapped the plug wires to see if I could get it to change cylinders, but it stayed consistent with cyl 3. Suspecting the coil pack, I installed a new one.

*a few days later, the misfires become more frequent and more intense. Flashing CEL and misfire codes 16684 (multiple cyl misfire), 16687 (cyl3), 16687 (cyl5), 17708 (misfire detected, probable reason low fuel).

-Wife says she thinks it's only happening below half tank of fuel. I changed the fuel filter, added injector cleaner, had her change gas stations and keep the car above 1/2 tank. I removed all the vacuum lines and replaced them. I changed the coolant temp sensor. I also replaced that problematic suction Y pipe while I was in there.

*issue returns, but now with all the previous codes plus 16688 (cyl4), 16686 (cyl2), and 17746 (camshaft position sensor g40, open or short to plus p1338-35-10). The car stalled at an intersection and took a bit for her to get it off the road. I picked up the car to bring it to my garage and it fired right up, idled smoothly and pulled away with no issues. About 5 minutes into the drive it felt like it was on 3 cylinders... Then it was fine again... then it stopped completely about a block from my garage. I finally got it started and into the driveway.

*I parked it for a week or so. I stopped by to get something out of it and it fired up and idled smoothly-- but I couldn't work on it that day. Next weekend the car would not start. The engine would spin and spin and it would start to smell of gas. One time it actually started, but it felt like it was just dieseling and the throttle had no effect... it quickly died again. The only code it's getting now is 17746 camshaft position sensor g40, open or short to plus p1338-35-00. (the description for this code is slightly different than the first 17746 code for some reason)

-I read that camshaft position sensor usually shows up when the timing is off... I put the car into service mode and checked the timing. I did not have the correct tools to lock it, but I used a straightedge to see if the marks were level or if I killed the tensioner... but it all looked OK.

*The car has not started since the day it idled smoothly in the driveway...

Do you think the next step is ECM?

Control Module Part Number: 4D0 907 551 AH
Component and/or Version: 2.8L V6/5V MOTR AT D04
Software Coding: 06252
Work Shop Code: WSC 02325


Thanks for any help.

sheeppig

Oh, poor man, like me, give you a huge......My 99 A6 c5 2.8L quattro put me almost exactly the same situation like yours did (My wife was stuck at an intersection too)! Anyway, my experience might help you a little bit.

*Check the coil pack again, it might fail again. Pull the wire out and put a spare spark plug back on and hold the gound-end to the gound of the car, then start the engine shortly to check the spark. If the spark is not strong enough, then it means something (short?) killed your coil pack again. You smell the gas means it does't has combustion in cylinders.

*ECM should work fine, I tried this too, bought an ECU and still be the same.

Peter Badore

You should do a compression test to see if the source of your problems is a skipped timing belt and bent valves.

vortexblue

Thanks for sharing your experience, it does sound similar.

I do have the original coil still--- if my new one is completely fried, the original coil should still be *slightly* ok, since it was changed out when just cyl 3 was misfiring. It would be worth a shot to swap it out to see if it will at least start.

I had planned on doing a compression check soon-- I kept putting it off because the car started and idled just fine, then the next turn of the key was a no-start. No noises or drama. But, like the timing belt check, it's worth checking.

vortexblue

I popped the old coilpack (with only the intermittent cyl 3 misfire), and the car fired right up and idled smoothly.

Good call!

Was a short in the wiring what killed yours? My next step is to trace the wiring, I guess.

Thanks for the help!

sheeppig

Haha, happy to hear that, looks we are on the same track. Check this as well:

1. Check the voltage between the engine (focus around injector pipe) and the negative terminal of the battery to see whether has any current goes throught it.
2. disconnect the harness from the coil pack and check the voltage between the terminals in harness and negative terminal of the battery.
3. If yes, disconnect both terminal of the battery and test it again. See what happen.

Sounds silly, check the voltage between ground to ground, but I found mine has 0.5 voltage current goes throught it even I disconnected the battery entirely. Next I am going to do some better grounding for the engine and see what will happen.

Share you more what happened on mine and something I thought:
Fault coding
18010 16795 16825 18032 18014, (others like 16684 Random/Multiple Cylinder Misfire Detected would disappear when your engine goes smooth again)
I have no clue about how to check and narrow down the issue about those codes right now. I suspect that the 18010, 16795 and 16825 are main reason makes coil pack goes wrong.

Hope those could give you some hints and let me know what you found. My email: leeyuyang@hotmail.com
Thanks.

Mr. Timewise

I'm somewhat hesitant to just throw another theory out there, but...

There might be an intermittent internal short or open circuit within one or both of the "Ignition Control Modules" of your engine. On the 2.7T these ICM sit right on top of the air intake duct at the right side of the engine below that pop off plastic cover.

There are two electrical connectors attached to each ICM. The ICMs are held in place with two bolts, and there is a coating of white thermal transfer paste between the module and the top of the air intake.

Unfortunately these parts are expensive. The part number for a 2000 A6 2.7T is "4A0 905 351 A". I think the 1999 would use the same part, but you must check with the dealer...or read the part number off the part now in the car. The letter at the end of the part number is important.

Here's a photo taken by AudiWorld member sanchir82. Look in the classifieds for his "Audi C5 A6 Ignition Control Module 4A0 905 351 A" ad.



I have a spare ICM as pictured here. Want to try it? Where are you located?

SloopJohnB@mac.com

I won't say WHY the white thermal paste was gone between the IC and the heat sink, but one theory is that it got washed out when someone whø shall not be named cleaned the engine with Gunk or some other engine cleaner.

SloopJohnB@mac.com

Expensive when new, used on ebay, not so much.

Mr. Timewise

Are you point three of your fingers back at yourself?