No offense intended, but I really hate how many people first assume many problems are vacuum leak related. No, it is most definitely NOT a vacuum leak, not plugs, not coils, not ignition...Runs like it has a 'hot' cam, also gets about 5 MPG less than it should...like a cam with higher overlap...(also, correct me if I'm wrong, but how would an intake vacuum leak cause misfires?, and then, on top of that, on only bank 2 of cylinders?)

 

You can get misfire due to vacuum leak. Incorrect fuel and air mixture will not detonate correctly. And the reason that I am suspicious of vacuum is the fact that the car runs good at high RPM. Typically a small vacuum leak becomes irrelevant at high rpm due to high volumn of air required. As for the question about affecting only bank 2, who knows you might have a crack in bank 2 intake or something. In addition, if it was timing related, it would run crappy all the time. Timing problem will definitely throw a timing related code as well, which you do not have.

Also as I mentioned earlier, check ignition related issues. If your car is ABZ, then you have 2 control modules and failure in one will kill one bank. Simple way of checking is to swap the control modules and see if the misfire locations change.

My rule of repairing car is that, unless you know the exact problem, repair the least expensive related option first.

 

I already swapped the ignition modules and even purchased a new one to be sure. No change. My question would be then: Where could a vacuum leak possibly be located that would be so bad to cause a whole bank of cylinders to misfire, but without a sound, and doesn't affect idle RPM, just low RPM power? If you had that kind of vacuum leak wouldn't you obviously hear it? / wouldn't it cause a severe lean condition so that you would have a fast idle or a lean related code? I've even created a vacuum leak just to see the results...nothing like what I'm experiencing.
Can you just assume it's not a leak and suggest what timing issue for me to check? The previous owner indicated the belt had been recently changed, but he wouldn't supply documentation, so I believe he may have done it incorrectly himself!

 

First of all, for your future referernce, you will get a lot more input if you start a new thread instead of attaching on an old thread.

Now to your issue... Lets start from the beginning. You are saying that your car idles fine. Miss fires during low rpm and runs fine once again above 3000 rpm? You bought the car the way it was... Also it is giving you some bank 2 misfire codes. Can you start by giving us the exact year and engine code? Also what are the exact OBD codes you are getting? Also what have you tried so far? Sounds like you bought an ignition module but didn't work?

 

It's definitely seems to be a mechanically retarded timing issue, hence the low vacuum at lower RPM. I took it to local shop and they confirmed, no vacuum leaks, but they don't do timing belts for A8s. (Also, the misfires MAY? be unrelated to the timing issue?...)
It's a 1997 A8 engine code (?where do I find it?). It seems to miss only at idle and low RPM (under 2000 RPM), high load.
Codes: P0300, P0305, P0306, P0307, P0308
Stumbles a little / lags, if in 3rd or higher gear between 1000 - 2200, when you step on it. Gradually gets better between 2200 - 2800. Pulls harder once it gets to about 2800 and above, but still doesn't have all the power it should, due to the retarded timing...

Have you ever performed a timing belt change on an A8? All I was asking is whether it sounded like the timing belt is incorrect, or if it indicated a cam chain, int/exh cam timing problem. I guess it's more likely the timing belt, since most people wouldn't have any reason to mess with the chain. I have the timing belt procedure and tools now, and will check the belt timing when I get some time in the next couple of weeks or so...

 

Your car is ABZ. That wast the only 1997 US spec 4.2 on A8. (S8 was AKH). Odd thing is that you are not getting any timing related trouble codes... You usually do if the timing is off.

So going back to your question, (First of all, I have not personally changed any timing belt on 4.2. but on a few 2.8.) the reason that I am trying to stop you from assuming the timing belt is that it is really complicated to deal with, and you need to have special tools. Since that there is no vacuum leak, and you confirmed that the ignition source is fine, I suggest checking couple of things prior to opening up the car for the timing belt. 1) Do you have properly working EGR system on bank 2, including valve, solenoid, and oxygen sensor? 2) How about fuel rail? Is the line feeding bank 2 in good shape?

Other than those two options, I don't have any more suggestions. You may find this website helpful for working on timing belt.

http://www.audipages.com/Tech_Articl...breplace0.html

 

op: im almost sure your timing chain is off. I have been rebuilding a set of heads for my a6 (aha engine). I just finished one head and starting taking apart the second head. I decided to count the rollers and found there were 14 rollers between the marks. MY HAYNES MANUAL SAID THERE SHOULD BE 16!! at first i thought, maybe they were simply mis timmed but the engine the heads came from ran perfectly and have no faults. I also had another set of aha head laying around so i checked me also. 14 ROLLERS AGAIN!

So now im alittle confused. it seems my manual is incorrect and ive checked two sets of heads and both have 14 rollers, not 16. i found this thread very interesting:

http://forums.audiworld.com/showthre...+chain+rollers

i know this is a 2.7t engine but they two engines are very similar.



this hand drawn picture from that thread LOOKS EXACTLY LIKE MINE before i disassemble the heads.


I have come to the conclusion that my Haynes manual is incorrect. I have two set of heads with 14 rollers between the marks. To be sure, tomarrow im going ot go to the junk yard and pull the valve cover off another engine to triple check.

 

Sorry for the long delay in posting (back from Jan '09), but I did solve the timing issue I had with my '97 A8 back in March, I just forgot to post the answer. As I suspected, the mechanical timing was off! The outer ring of harmonic balancer (which has the TDC timing mark) had spun about 30 degrees relative to the hub (which has the keyway), so what obviously happened was when the previous owner changed the belt (just prior to selling it to me), he put it together wrong, because the TDC mark on the crank was not accurate. So beware that those harmonic balancers can fail/ be incorrect. Double check the crank is truly at TDC mechanically.

 

hey guys, i figured i would follow up just for future reference with anyone else who has the cam timing problem.

This was a very confusing experience for me. It turns out that on the 2.8 and 2.7 engines there should be 14 rollers between the cam marks NOT 16. I set my cams with 14 rollers and i just started the car today. It runs perfectttttt. No check engine light, No pending codes, Idles and rev like a dream. I hope that clears it up as I'm sure there will be allot of people with the same confusion that i found when setting the timing on these heads.