Hi, putting this out there for some ideas or feedback.
I have a 2000 A6 2.8 quattro, 250000 kms.
Been getting P0300 - Random/multiple cylinder misfires, P0304, P0306 & P0305 since purchasing vehicle with 234000 kms.
Timing belt done at 198000 kms (Audi dealer).
Replaced since purchase:
- spark plugs, wires, coil pack.
Been diagnosed by Audi mechanic, no definitive answers.
I bought Ross-Tech cable and software - no other engine fault codes than those mentioned above.
Fault is triggered only above 3000 rpm, under either moderate to hard acceleration or at highway cruising speeds when rpm's reach above 3000 rpm. Fault will also appear if car is in park and I rev the engine above 3000 rpm.
Overall the car runs very good, easy starting, very good fuel economy, shifts very good but I can feel the miss or hesitation with moderate to hard acceleration just before throwing the MIL light.
Any thoughts or ideas? I am still getting familiar with the Ross-tech software. Anything I can use in this software to diagnose?

Thanks!

 

hi there i saw your post and it is related verry well with my problem , did you find what was wrong ?

 

No answers yet.
Had the car in at an Audi shop (not dealer but is a former audi dealer mechanic) and he is the second mechanic to suspect that the timing belt might be off for the left bank (cylinders 4,5,6). There are no other diagnostic codes. Just the random cyl. misfire and than misfire cylinders 4,5,6. He also did throw out possibly a plugged catalytic converter for the 4,5,6 bank.
If I wanted him to investigate further, he would fist drop the exaust to check the catalytic converter before taking apart the front end to check the timing.

Have you had any engine work done recently (i.e. timing belt) that you have had the light come on after or has this been a longer term thing?

 

What about the cam chain tensioner, with what you describe, the tensioner may not be able to do it's job under varying oil pressures

 

The cam adjusters are mechanical on the 1.8T, 2.7T, 2.8's etc.

3.0L / 4.2L among others use solenoid actuated cam adjusters that regulate oil pressure for controling cam timing.

Sounds like your mechanic knows what he is doing. Restricted exhaust or Timing issue are the two prime suspects and I'd lean towards Timing based on symptom you describe.

 

My engine is 4.2l and i had work done on the timing belt but,i get missfires on cyl 5,cyl 7 and cyl 8,never on the 6th .this is the second time i do the timing belt on the car first time i did it without the tools and now i replaced all the parts related and used the tools +bentley ,consulted also the alldata manual .before i did the job the second time i started with sparkpulgs and ignition coils , vacuum hoses Maf .After i did the Tbelt i also got the same cyl missfire but the car is not stalling anymore .right now i suspect that the chain tensioner maybe has worn it's pads ,or it is not good anymore (but i cecked it ,it's in specs of resistance !) ,or i have stuck lifters or bent valves ,the last one i doubt cause i cecked compression and i got 180 psi .in your case i think as your mechanic that the timing is off on that bank but is just a thought not a warranty .I read a while ago that you can ceck the cat to see if you hear rattling noises when you bang on it with your hand ,never tried it myself .i will keep you posted if i find something about the matter ,and i appreciate your response .

 

MIL light update - the mechanic cut out the catalytic converter to inspect, all is clear.
Next step is the timing belt check. Will check back in.

 

Update #2 - timing belt checked and everything is okay.
A little more head scratching and the mechanic is thinking cam tensioner follower (this would at the back of bank 2, cyl 4,5,6). I hope I have the right term.
I would further describe the problem with the car as not a miss but a hesitation, as if something is trying to play catch up to when I push the thottle harder. Acceleration seems flat then as if a turbo kicks in.
Still throwing the same codes.
I would like to better understand the operation of the mechanical internals of this 2.8 (i.e variable intake, layout of the cam and associated hardware, etc...) My Bentley service manual does not really touch on this.
Any goods links out there?
Thanks.

 

I was looking and asking alot about this ,in my search i came across some videos on youtube regarding chain tensioner on audi's engines ,the tensioner (not the mechanic one ,the hydraulic one ) causes some diesel like noise when idling with warm engine ,try to look on youtube , i do not have a link handy.A friend of mine told me the mechanic replaced only the pads for the tensioner ,you could find those on ebay ,costs between 49 to 79 $ a pair alot cheaper than replacing the whole tensioner about 600$+ labor ,but in order to change it you have to remove the cam followers ,some procedures say that you could do it by removing only the intake one if i don't mistake .I will replace mine in a couple of months because i tried all the rest ,i also want to use vag com to log my engine and find out more about the possible cause .Meanwhile i seafoamed the car and it runs sooth but i still get the missfire on the three cylinders (5,7,except the cyl 6. I'll post any new findings and help if i can .

 

I think you are looking at the Moon for something that is on Earth.
Check your spark plug wires and replace them first. They are deep inside the engine, get hot and the rubber gets bad. When you accelerate the coils give more voltage and you get shorts.