B6 Misfire?

[newsh]

I've just had a drive of a friend's B6 S4

The car feels really good on a light throttle but seems to misfire when you put your foot down, Back off and it picks up speed more smoothly.

VagCom shows no fault codes.

Any ideas chaps? Any measuring blocks we can look at? does VagCom log misfires?

Or.. Is this what happens with the carbon build up?

[quattro-nick]

i had once a b6 s4 v8 with simular problems,only the engine was running on all 8 cilinders.
it had sometimes a vibration that came and went away.
i thought it was a coil so replaced all 8 coils but it was not solved
the problem was the dual mass flywheel

[Monkeymagic]

You can log misfires in windows 15 and 16 may run into 17 on v8

[Monkeymagic]

Is this a direct injection engine? If so carbon build up is a major pain in the arris

[Monkeymagic]

Just checked it is measuring blocks 15 16and 17. B6 is not direct injection so unlikely to be carbon build up. Start with obvious things like plugs/gaps I say.

[Monkeymagic]

Check blocks 90 91 92 for evidence of tensioner /chain stretch..

[Error404]

MPI so no carbon buildup problems to worry about. The tensioner issues normally show up as a VVT actuator adjustment code, misfires should throw a code too.
Does it have standard downpipes on there?

[Monkeymagic]

I'd expect it to throw a misfire code in seconds if it is actually missing too.

[newsh]

Thanks for the info Monkey I'll pass it on to him. I was told on SRS that coilpacks can be a problem and there was a recall, sometimes they don't show a code.

It might not be a misfire, maybe just goes flat as you give it more throttle, quite odd. I'm always suspicious of cars that seem sweeter at part throttle, my ur did this when the FPR was seized up.

[newsh]

MPI so no carbon buildup problems to worry about. The tensioner issues normally show up as a VVT actuator adjustment code, misfires should throw a code too.
Does it have standard downpipes on there?

Standard car AFAIK although he said it had had some sort of software upgrade..

[sam80quattro]

as per monkeymagic.. gotta be worth changing plugs 1st?

[Monkeymagic]

I believe Alex owns,one of these so probably knows his way round these engines.
However watching measuring blocks for misfires would be a good start. I may be wrong but I have heard about the precats falling apart and blocking the exhausts and causing running issues. It may be why Alex asked the question?

[newsh]

I suggested looking a plugs so I think he will do that first.

[newsh]

So misfires in 15,16,17.
Wish I'd known that when car was here.

[1781cc]

I had a major misfire problem on my first B6, I replaced all the coil packs (which can be a pain removing all the airbox and stuff) and it was still there, took it to 3 places and no-one found a solution, eventually ended up at MRC and Doug found it was a problem with inlet air flap which moves as you go past 4K revs.

He cable tied it as he said it was pointless anyway and I did another 12000 miles over 2 years in the car with no misfire before selling it on so I could buy something else

Don't despair yet, have a look at the flap!