Need some help with my E39 540i

Hey wanted to try here also to see if you know whats going on.

If you drive normal the car drives fine.

As soon as you use the kickdown or just start to go fast (high rpm) then it suddenly starts acting like its misfiring, shaking alot and not taking throttle very well. As soon as you turn of the car and start it again it goes away until you goes fast again.

The dealer read out the errors and said it was a coil. So he replaced one, and the same day it started doing it again...... So he replaced another coil, and guess what.

I dont really trust that Dealer so if you got any suggestions please let me know. Unfortunately i dont have the codes. But i have read that this is a well-known fact for BMW's with the BREMI coils but i dont know if my car has them or not. Just want to be sure before i go ahead and order 8 new coils.

sounds like clogged cats, take o2 sensors out which should ease any back pressure on the cats and the car should stop misfiring

Not a bad idea, its also making a little rattling noise from the exhaust.

Okay guys i FINALLY got the codes read. It is misfiring on cylinder 5,6 and 8, and a bad Catalic converter (02 sensors are reading bad A/F Ratio).

So, what would you guys check/change first? I am leaning most towards the cats being causing the major problem because the problem is only when you drive fast/high rpms, and no problems when your just going easy/slow.

It was the cat !!

I am glad everything was sorted out for you!