Misfire under high engine load - help!

[Toymad]

I've been chasing a misfire for about a year, and two different garages haven't been able to sort it and the local rolling road flat out refused to look at an RS4:( Any input gladly received, these are the symptoms:

Misfire under high engine load, ie 6k revs and booting it in 3rd, will deliver power for ~1-2 seconds and then stutter. Off the gas (eg to change gear) and then back on the power and it will be fine for another 1-2 seconds before misfiring again.

Variations: Sometimes will misfire at lower revs, eg lugging in 4th at ~4.5k revs. Raising revs gently to the red line doesn't result in a misfire. Seems to be better after a really good blat and worse after sitting on cruise at 60mph for an hour or whatever.

Possibly related, possibly not: Idles and runs a bit rough and cranks longer before it starts when its cold.

Changed fuel filter
Changes spark plugs
Inspected fuel tank for crud, blockages.
Carbon clean approx 10k miles ago
Changed some vacuum thingie, sorry can't remember what the garage said it was.

It really feels like fuel starvation to me, anyone else had these symptoms?

[QuRace]

It really feels like fuel starvation to me, ...

That's what I immediately thought, too: LPFP/HPFP. Did you check for any related codes?

[Toymad]

It's not throwing any codes out, at least, none that my cheap code reader sees.

[12th]

Fuel pumps? There are two.

[Covkiller]

Have you checked your coil packs?

[jack_hamlett]

Did you find the problem in the end?


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[TrevoRS4]

Did you find the problem in the end?


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This!!?

[rshales007]

An old thread now, but RE Performance did a couple of videos on an RS4 with a similar sounding issue.

Part 1 :- https://www.youtube.com/watch?v=KwVihDuVwSs

Part 2 :- https://www.youtube.com/watch?v=CkX2RtNIbdU

Well worth watching.