Cat issues , any thoughts??

[RFaber]

Hello crew! Well, I have been chasing down, what my wife was certain was , a heat shield rattle in my rear header (I have the m54b30 3 litre engine)
I couldn’t find anything that would rattle while I was underneath, no steering lines, no pebble stuck on a muffler, no nothing!!!
Last night I pulled the top o2 sensor and saw that the top of the cat was nearly covered ( maybe 80% covered) with this white hard crust! I attached the camera to a pic, and tried to pick away at it, but it was pretty solid!!
I’m figuring the cats are toast (after 350,000km!!!)
Probably going to get an aftermarket set odd eBay or so!!
Is my predicament normal?? Any other ‘high milers’ have to replace the headers??
My fuel mileage is consistent around 12-12.5 litres per 100km
I’ll attach photos once I resize them

[Effduration]

If you are not getting a code related to cat efficiency I would not replace a cat. My e39 with same engine has 400k miles. I am getting occasional Cat error codes, but I will try the rear 02 threaded spacers to solve that problem.

I suppose if the rattle was loud and obviously a piece of broken cat material, I might replace it.

[RFaber]

Here is a photo of what I’m looking at, this is the cat as viewed through the o2 sensor hole

[srmmmm]

I'm at 590,000KM on the original convertors with no error codes on them. But I only use Shell gasoline and no fuel system additives.


2002 X5 3.0 367,000 miles
2014 428i 65,000 miles


2004 325i Sold at 123,600 miles
2001 325i Sold at 66,000 miles


1970 Firebird Under restoration

[bcredliner]

When is the rattle heard? Over bump, accelerating, etc. There should be error code for bad cat. Have you checked for codes?

[RFaber]

No codes, I had a misfire code last summer, while hauling my trailer up a pretty good size mountain pass. Changed plugs and all the ignition coils. It’s been good since! O2 sensors seem to be outputting proper values, I use mid grade - 89 or premium -91
The rattle is at startup, and while idling, I don’t hear it during highway driving,
I’ve gone underneath and it’s coming from the rear cat just before the pipe bends to travel to the rear. It’s not a heat Shield, I’m suspecting the packing material around the cat has shifted and allowing the rattle, the cats looked plugged. So I’m changing both! And I may do my valve stem seals, and possibly the head gasket depending how the exhaust bolts come out!!!

[oldskewel]

Originally Posted by RFaber

No codes, I had a misfire code last summer, while hauling my trailer up a pretty good size mountain pass. Changed plugs and all the ignition coils. It’s been good since! O2 sensors seem to be outputting proper values, I use mid grade - 89 or premium -91
The rattle is at startup, and while idling, I don’t hear it during highway driving,
I’ve gone underneath and it’s coming from the rear cat just before the pipe bends to travel to the rear. It’s not a heat Shield, I’m suspecting the packing material around the cat has shifted and allowing the rattle, the cats looked plugged. So I’m changing both! And I may do my valve stem seals, and possibly the head gasket depending how the exhaust bolts come out!!!

Definitely possible to get the exhaust manifolds off with the head still installed. I did that on my M54B30 last summer. That task was one of the tougher parts of the whole experience, but definitely done. If you search for posts of mine, I think I mentioned the difficulties, and maybe tricks I did to get it done. So I would definitely not be looking to do a head gasket just because it's tough to get the exhaust manifolds off.

Good luck on the work.

[RFaber]

Thanx, I did read your posts, I figure if I break a bolt or two, the head will probably have to come off for me to drill out the broken bolts!! I’m no stranger to this sort of work, I would just rather not have to!! Unless of course the white residue is caused by a coolant leak into the exhaust! Wish me luck! My new cats/headers are on the way!!! I’ll post ability my experience once I’m done! Thanx!!

[Effduration]

Are you using stock, OEM cats/ exhaust manifolds?

[iansanderson]

Originally Posted by RFaber

Here is a photo of what I’m looking at, this is the cat as viewed through the o2 sensor hole

Based on that pic, that cat is becoming clogged from what looks like deposits. Misfires, and low engine output are in your near future. Rockauto has a bunch of aftermarket options. My cats on my 04 went around ~150K mi with a P0422 catalyst inefficiency. I think I paid $800/ea for OEM, and just did both "while you're in there" since they both had to come out anyways