BMW 4.6 is poor acceleration and hesitation

[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]

...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]

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.

[sethhatfield]

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

[bcredliner]

Originally Posted by Aman

Thanks for your help
After I took the car to the garage again today they reset the engine management light
Now when the car idles there is no misfire again
It seems me making the car go to 4000 rpm causes a misfire at approx rpm, if I do it enough times the EML stays on and the misfire stays, until the EML is reset... so it seems...

Your are correct, it will come back because the the computer will get the same signals that caused the EML to come on previously.

Are you still at the shop or is that all the shop did?

[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

[Aman]

Originally Posted by bcredliner

Your are correct, it will come back because the the computer will get the same signals that caused the EML to come on previously.

Are you still at the shop or is that all the shop did?

That's all the shop did as they were only open half day
They didnt charge me though!
Should I take my car back to the BMW specialist and let them investigate or just go to an exhaust place and get the cats looked at?

[bcredliner]

Originally Posted by upallnight

Sound like your converter are busted up inside and choking the engine because it can't exhaust the gas fast enough. There was another guy that had the same issue.

Here's the link http://www.xoutpost.com/bmw-sav-foru...der-fixed.html

Before buying new converters, here's a video link on how to test the converters.

https://www.youtube.com/watch?v=9TlygJMxTps

If the exhaust place has the capability to run the test of back pressure (see video in the above) or similar appropriate test, yes, if not, there is a chance you will be buying a new cat that you don't need (I don't think that will be the case but it could).

If you replace the cat and it goes away, one of the two shops you visited that has the capability to run engine tests should test if there is still something going on that caused the cat to fail. Assuming the coils that were replaced were actually bad, the fuel not completely burned could have destroyed the cat.

To be sure it won't happen again, the engine should be checked to see if the root cause has been eliminated.

[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

[bcredliner]

Just thought of something else. If you are looking to increase performance and get a louder sounding exhaust---

Assuming you need to replace a cat(s), and you have the budget and likely can wait a few days as they won't be in stock, consider a low restriction cat. It would be necessary to replace both sides. You need to be careful that they will still pass any emissions test there but--just something you should know.