BMW 4.6 is poor acceleration and hesitation

[pezho405]

Could you maybe get under the car and bang on the cats to hear for the rattles?

Sorry for not being of much help

[Aman]

Originally Posted by pezho405

Could you maybe get under the car and bang on the cats to hear for the rattles?

Sorry for not being of much help

Any help is much appreciated - thanks for your advice

[Aman]

Update: started car just now, and it misfired at idle (engine light is off)
Drove car gently, and misfire went away

[bcredliner]

Find someone with a gauge to measure back pressure.

[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.

[Aman]

Just out of interest, is each tail pipe for a separate bank or do they join together?
It's just that I notice more noise and steam out of the right one, the left tail pipe has a lot less steam and noise

[sethhatfield]

Mine are separate so yours probably are too. Both mine were bad but the driver's side was worse.

[Aman]

Originally Posted by sethhatfield

Mine are separate so yours probably are too. Both mine were bad but the driver's side was worse.

Update:
Hi I got under the car today.
I thumped the left cat with my fist (the same side as cylinders 5,6,7,8) and I could hear stuff rattling around inside the cat
I thumped the right cat, but no noise from that one
Further confirms your suggestion

[Aman]

Originally Posted by pezho405

Could you maybe get under the car and bang on the cats to hear for the rattles?

Sorry for not being of much help

Got under car today and bashed cats with fist, left one rattles, right one is ok
Cheers

[upallnight]

Is the cat on the same side of the engine that you are having the misfire issues? If so, the cat was probably destroyed due to running too rich on that side of the engine. Unburnt gasoline enter the cat from the cylinder (s) that were misfiring resulting in the cat over heating and self destructing. You need to find out why you have the misfire or else the new cat will suffer the same fate as the old one.

One place to look is the DME. There was a guy on another forum with a BMW 540 M62 engine that had a misfire until he looked at the DME. The ignitor circuit was toast.