BMW 4.6 is poor acceleration and hesitation

[Aman]

Originally Posted by sethhatfield

It's the catalytic converters are clogged and broken apart inside their shells. I had the same problem and had mine replaced with a pair of universals for $364 and I got all the power back. I wouldn't rev past 4000 rpm when flooring it. The muffler guy cut them off and chunks of crap fell out of them.

Thanks for your input.
Did you have the rattle like the one in my video on page 2?
Do you have a 4.6 too?
What made you suspect the cats rather than coils etc?
Many thanks for your help

[sethhatfield]

I had bizarre seemingly unrelated codes also. Misfires on #8 and such.

[sethhatfield]

I had a rattle but the material was so crammed in there by the end it stopped and was plugging up the exhaust. Yours is probably moving around in there still which is why it gets better occasionally. Mine is a 4.4 but I doubt the cats are different. My engine has 130,000 so we're not far apart.

I knew the coils wasn't it because I swapped them and the misfire stayed put. I also swapped plugs around.

I'm afraid it will come back after the crap in them blocks the exhaust again.

[Aman]

Originally Posted by sethhatfield

I had a rattle but the material was so crammed in there by the end it stopped and was plugging up the exhaust. Yours is probably moving around in there still which is why it gets better occasionally. Mine is a 4.4 but I doubt the cats are different. My engine has 130,000 so we're not far apart.

I knew the coils wasn't it because I swapped them and the misfire stayed put. I also swapped plugs around.

I'm afraid it will come back after the crap in them blocks the exhaust again.

Thanks for your help.
Suspecting the cats is seeming more likely now
Is there any chance you could have a look at the video of the sound I posted on page 2 and let me know what you think?
Many many thanks

[sethhatfield]

Originally Posted by Aman

Thanks for your help.
Suspecting the cats is seeming more likely now
Is there any chance you could have a look at the video of the sound I posted on page 2 and let me know what you think?
Many many thanks

Yes that is the material "honeycomb rock" inside the steel can shells banging around in there I'll bet.

Worst case, you change the cats a year too soon because they are going to need replacing anyway.

[Aman]

Originally Posted by sethhatfield

Yes that is the material "honeycomb rock" inside the steel can shells banging around in there I'll bet.

Worst case, you change the cats a year too soon because they are going to need replacing anyway.

Hi just wanted to check, did you ever find something wrong with the engine that caused the cats to fail, or did they just fail without anything from the engine causing them to fail?
Thanks

[sethhatfield]

Originally Posted by Aman

Hi just wanted to check, did you ever find something wrong with the engine that caused the cats to fail, or did they just fail without anything from the engine causing them to fail?
Thanks

No just time and mileage.

[bcredliner]

Originally Posted by Aman

Thanks for your help.
Suspecting the cats is seeming more likely now
Is there any chance you could have a look at the video of the sound I posted on page 2 and let me know what you think?
Many many thanks

[sethhatfield]

...And BTW any universal 2 or 2 1/4" inch inlet/outlet catalytic converter will work fine. There is absolutely no reason to spend a ton of money on original ones unless maybe you're in emissions free California.

Mine look great and there are no codes. Performance is better than I ever remember. It revs all the way to 6000+ under full throttle in every gear.

[sethhatfield]

I've got a E39 M5 and I swear my wife and I are going to line them up and race.