# 99 C5 A6q Audi Avant; persistant misfire --> no start



## vortexblue (Jan 27, 2001)

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.


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