Well I'll try to make it brief:
did a timing job & a valve job which turned back into a timing job (due to a broken tension pully bolt) and back on the road.
Had lots of carbon build up on the head due to the timing being off from the first timing job - was off a few teeth.
Ran some lucas through the system and now I'm getti becasue I'm an idiot and didn't rent the tools.
Now I'm getting an occasional mis-fire (more like it runs with bad wires) and then it runs fine. does not seem to be tempature related. can happen after a mile or two or twenty and only last for ten seconds or so then runs again. took it in for emissions and it passed everything but the nox. can't run a scanner because I've tried 4 of them over the last couple of months and always get "communication error".
any clues?
thanks!

 

figure out why the scanner wont work..... this literally could be 100 different things causing this

 

let me do this again as it got jumbled when I posted it:
98' A6 2.8 Qttro 30V

I did a timing job & a valve job which turned back into a timing job (due to a broken tensioner pully bolt) and back on the road.
Had lots of carbon build up on the head due to the timing being off from the first timing job - was off a few teeth because I'm an idiot and didn't rent the tools.

Ran some lucas through the system and now I'm getting an occasional mis-fire (more like it runs with bad wires) and then it runs fine. does not seem to be tempature related. can happen after a mile or two or twenty and only last for ten seconds or so then runs again. took it in for emissions and it passed everything but the nox. can't run a scanner because I've tried 4 of them over the last couple of months and always get "communication error".
any clues?
thanks!

 

well I don't think it could be a hundred different things and if I could have gotten the scanner to work I would not be asking these questions. There really can not be very many scenarios for a car running perfect and then misfiring and then running perfect again after a timing rebuild and with high nox emissions.
any one else have an actual guess or suggestion?
I took it for a long drive today (about 120 miles and never once did it misfire) and then stopped to fill up before having it re-tested. as soon as it got the new gas it ran like crap for about 20 min and then ran fine again. It failed the emissions again
(2.2132) vs. the first test of around 2.4.
Thanks!

 

With all due respect I think Audifield has a point .. you are to close to the situation .. take a step back .. deal with what you know

you had lots of carbon build up on the head .. that are facts.. whether it was due to a timing issue is supposition on your part.

think this is due to timing may be related but does not make it fact. if you had the head off you were fairly deep into the engine and it could be many things. it is hard to diagnose without facts " guessing" wont get you anywhere except for an empty wallet.
You could possibly have unmetered air entering the system and throwing off your mixture. I have done many Audi timing jobs and it is fairly mechanical .. if it is set it is set. it is kind of like the RONCO sytem .. " set it and forget it" I guess oyu could have an issue with the VVT with the hydraulic tensioners but i doubt it . Is your car throwing any codes at all ? If the timing is even off one tooth on that cam you will throw a code .. if you aren't getting codes i would go back to basics and check for vac leaks good ignition wires etc,

Good luck

 

Thanks Airbag, yea I was thinking vac leak, dirty maf , etc.
I don't think the timing is off due to the intermittent misfire.
I would think perpetual misfire but I'm no mechanic by any means.
I have owned foreign autos for about 35 years and have always tried to work on them myself. I have read and read on high nox and it seems it could be several things ie: vac issues, egr (kombi)valves, bad o2 sensor and bad cats. The mystery is that I had it back togehter and it ran perfect for about a month until the bolt on the tensioner broke in half (bizzare circumstance where a lost bolt found it's way into the timing area and logged into the TB tensioner - in my driveway while idling to leave !) and almost f'd up the whole car. I did the whole TB thing again (could now do it in my sleep) and retooled the block but did not touch the cylinder head again. I was expecting the valves to be toast again but a visual inspection ( air intake removed) and compression test showed no ill affects. I am wondering if using the LUCAS blew so much crap out of the engine that it is now running too rich. Plugs are all burning perfect and to me that says most things are OK in the firing process. So off again to look things over and I'll post. What sucks is now colorado will not give you any more temps to "drive and fix" after the initial 10 day temp. They will only give u one day temp and you are suppose to have it towed to a dealer to fix. I told the gal at the registry "so what now fixing your own car in these economic times is illegal? How do I drive it for testing and How do I get it to the emissions?" she had no answer. Is it just me or is this county PHUCKED_UP?

 

Is there one or two knock sensors on the V6?
If you can get to the connectors, it's easy to check them.
My 2K4.2A6 V8 had two sensors, under the intake manifold. You don't want to have to replace them!
Maybe the V6 is different.

Anyway, Bentley says to test the 4.2 sensors by continuity between any of the three terminals. Any combination of two should be an open circuit. A short means a failed knock sensor.

If you get the scan running or another one used you might get a knock sensor reading when the engine is running crappy. I finally got a bad knock sensor reading with a running limp engine WITHOUT a CEL.

 

well I traced all the vac lines and found the one going into the right (not sure what the little deals all the vac lines connect into are called) "box" had broken free. It goes under the coil pack and into the plunger (again have no idea what this unit is called) in the center front of the air intake. I had to pull off the coil and the plunger unit to take off the frayed end and
reconnect. I also found a loose vac line to the drivers side kombi valve. I wish I had taken some pics (mmmmm next time) of all the vac lines. I'm going to start a new post in hopes someone has the diagram or is doing similiar work now. I'm possitive this has to be the culprit of the intermittent and occasional misfire as well as the high nox readings!
will check all vac lines and have emissions re-done and post.

 

do oyurself a favor . go to ecs tuning get some new braided vac lines and redo the whole thing. You really should have done this when you had it apart . those things see a ton of heat and the fire shield braid is probably disolving to as well as the brittle plastic bits if you have any left ..