Catalytic Converter replacement

[rharris99]

You could try that, but what is the condition of the air filter, fuel filters, spark plugs, O2 sensors, and commonly-air-leaking intake manifold gaskets? If any of those are bad, you could see an improvement by changing them.

Sadly, it seems very common to have replacement/aftermarket cats offer only a small (or temporary) improvement on emissions test figures.

I changed everything in 2012-2013...the only thing I didn't check is the intake manifold gaskets (after reading Timm's write up this may be the culprit )

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Cats can be killed pretty quickly by an over-rich mixture - and the V8's are notorious for it due to multiple vacuum leaks that skew the adaptations. Have a read of this:

http://www.meeknet.co.uk/e31/BMW_M60...cuum_Leaks.htm

Great stuff as usual...and it has to be one of these (I'm guessing the gaskets) that is the problem.

Thanks for the link!

[Wuffer]

For what its worth, my local exhaust specialist, who is also a Magnaflow Dealer will not install Magnaflow cats on any car as he says they don't last even for a year. Right after install, they are fine enough to pass aircare/smog testing but will fail within 3-6 months. This is based on his personal experience (he is considered the best custom exhaust shop in the lower mainland) and having to re-do the job over again under warranty. He will now only install Walker universal cats - and guarantee them. YMMV... but I wouldn't install Magnaflow cats on my car.

[rjbaren]

Where I live in the Midwest, cars 1995 and older do not have to go through a smog test. I removed my Cats, since they were rattling, per my dealer mechanic's advice. I have since replaced them with an aftermarket single converter 2 in 2 out, due to the smell my wife complained about. I am not sure what converter was installed, but the smell is gone. Now after reading this I am wondering if I should do the manifold nuts. What are the symptoms of the intake vacuum leak? My car seems to run well, but maybe it could run even better. Is this a maintenance item on these engines, or do we wait until symptoms occur?

[cel0202]

Thank you for this information. After reading this, I feel so fortunate passing all 4 of my smog tests since 2008. Fortunately I have some time until the next one... August 2016. I'll have to give some local muffler shops a call and see what brand they recommend and what type of warranty the cats come with.

Pardon my lack of knowledge, but does anyone have insight as to why the stock cats are so expensive and come with the entire exhaust system?

For what its worth, my local exhaust specialist, who is also a Magnaflow Dealer will not install Magnaflow cats on any car as he says they don't last even for a year. Right after install, they are fine enough to pass aircare/smog testing but will fail within 3-6 months. This is based on his personal experience (he is considered the best custom exhaust shop in the lower mainland) and having to re-do the job over again under warranty. He will now only install Walker universal cats - and guarantee them. YMMV... but I wouldn't install Magnaflow cats on my car.

[german wannabe]

Anything stock or dealer is more expensive but going back to what Wuffers mentioned and to explain further ....aftermarket cats have less precious metals and tend not to last as long as factory ones. This what I've been told by my smog shop.

[Timm]

Both my catalytic converters failed on my 840ci, one had started to melt, then other disintegrated:



In my history file was a bill from BMW for replacement of both cats four years ago - total cost of replacement £1700

I had both replaced by a custom shop with 200 cell Longlife units - total cost of replacement £500. I've passed two MOT's (UK smog test) with them fitted. Performance was noticeably better than when I first had the car due to the better gas flow. My feelings are obvious - I could have them replaced another couple of times and still have £200 in my pocket!

[Prometheus]

I've had great luck with using Random Technology brand catalytic converters on race cars (for street class compliant cars) and miraculously it passed a sniffer test on a rotary that was pre mixing 2 stroke oil into the gas.

http://www.randomtechnology.com/products.html

[slickbeamer]

if anyone else replaces your stock cats please save them don't let the exhaust shop take them i will buy them from you! pm me if you do!

[Litman]

For what its worth, my local exhaust specialist, who is also a Magnaflow Dealer will not install Magnaflow cats on any car as he says they don't last even for a year. Right after install, they are fine enough to pass aircare/smog testing but will fail within 3-6 months. This is based on his personal experience (he is considered the best custom exhaust shop in the lower mainland) and having to re-do the job over again under warranty. He will now only install Walker universal cats - and guarantee them. YMMV... but I wouldn't install Magnaflow cats on my car.

Any chance you know or could get the Walker model number your local specialist uses? The Walker website states #15022 as a direct replacement however the dimensions (width) seem too big plus it has an air pump port. In the course of building a new exhaust I found that the OE cats in my (your old) '91 850 6MT are one their way out, literally. Looking for a reliable weld in replacement. Walkers seem reasonable if I can get the proper configuration.

[cartoonz]

The Walker #80832 are 50 State compliant and do not have the stupid air bung on them...

[tvjake2]

[QUOTE


Were your old cats cut and new cats welded in to the existing pipes?[/QUOTE]

No they were new, aftermarket cats.

[Hyper]

...aftermarket cats have less precious metals and tend not to last as long as factory ones...

Magnaflow had at one point divided up their catalog into economy/ceramic, heavy metal, feature engineered, and California. California versions may-or-may-not be different from the 49-state version, but it is tracked and can be more expensive by far.

Faced with restoring a rare 30-year old, I spent money on the better materials rather than market/regime.
A Magnaflow heavy-metal was walked in from out of state, side-stepping the ban on sale, and installed personally, side-stepping the ban on shop installs and assuring a quality level.
It is not regime stamped, but neither were cats from 30 years ago.

[mattsimis]

The Walker #80832 are 50 State compliant and do not have the stupid air bung on them...

This one? Its 1 in 2 out and appears to have a O2 bung hole?

[cartoonz]

No, you need the O2 bung... the other Walker part# mentioned earlier has a pipe that extends from the side of it, then crooks at a 90 degree angle for use one some kind of air pump that none of our cars have. Sure, you could use them I suppose, but you'd have to cap that off. The part# I gave (and you displayed above) doesn't have that appendage

[slickbeamer]

if anyone else replaces their cats PLEASE SAVE THEM! I can pay you up to $250 for your old stock cats!! even if they are bad!

[vet73]

Slickbeamer: sorry I didn't read this earlier. Just let shop throw away. Had my cats replaced by straight pipes as I was told my cats were blocking flow.after removal, inspection revealed NOTHING left in cat housing, absolutely nothing, inside. Just were empty cans. Guess all precious metals and other internals were blown out tail pipe. Intake rebuild and resealing and new O2 sensors took care of CE lights on cold mornings. Can't really tell much sound differences or smells either. Just runs better than ever. No smog tests on any cars, so that is not a problem for us here.

[slickbeamer]

damn that sucks exhaust shops LOVE taking advantage of people who don't know. the really dishonest ones will tell you you need new cats just to recycle the old ones that are worth more than the new ones! haha. PLEASE anyone reading this contact me before giving an exhaust shop your cats!

[ChrisFuture8]

I had to replace both cats in 2013. The OEM cats were replaced with Magnaflow's. Just had another smog check a couple months back and passed fine. The only thing I don't like about the Magnaflow cats is that they have a raspy sound under hard acceleration. As for longevity of the Magnaflow cats, I'm not arguing with Wuffer as I haven't really driven the car much at all. Probably less then 1500 miles in the last 2 years so can't tell.

[cel0202]

Reviving this thread... my apologies.

Well, it's been a year and it's finally time to replace the cats in order to pass my smog test by August. Based on this thread, it looks as if Walker cats are the way to go. Was #80832 the correct or incorrect part number? I did a quick search on Walker's website and it mentioned #80811 would be the correct one, and on Autozone, it would be #15196.

Any other recommendations that may have been discovered over the last year?

Thanks all!

[mojocoggo]

Not sure how much the Walkers are, but I've always used Magnaflow cats for CA smog. They're $198 each from pretty much any place that sells them:

https://www.summitracing.com/parts/m...FUdlfgodUeMGGg

Also I'm curious, how did you determine that you need new cats? They will last for 250k miles easily if they don't get soaked in oil, fuel, or coolant due to engine issues.

[cel0202]

My mechanic and I noticed heavy rattling about a year ago and I've been putting off the replacement until my next required test.

From what I keep reading, the Magnaflows will add a bit of growl to my car, but I'm looking for more of a quiet ride much like the OEM. Also, i've read that the Magnaflows don't last quite as long. How many tests have your Magnaflows gone through?

Not sure how much the Walkers are, but I've always used Magnaflow cats for CA smog. They're $198 each from pretty much any place that sells them:

https://www.summitracing.com/parts/m...FUdlfgodUeMGGg

Also I'm curious, how did you determine that you need new cats? They will last for 250k miles easily if they don't get soaked in oil, fuel, or coolant due to engine issues.

[mojocoggo]

I've never noticed a change in sound going from OE to Magnaflow cats. I also only want a quiet OEM exhaust sound so I've always paid attention to any changes. I can't say I have any long-term experience with Magnaflow cats, and I wouldn't use them on my own car personally.

My 850i had no cats when I bought it. I ended up just getting a used set of cats from a 60k mile car that was wrecked. I verified the smog history of the donor car (you can do so for free here: http://www.bar.ca.gov/pubwebquery/ve...pubtstqry.aspx) and it had passed every time it was tested, so I figured it would be a good bet.

I would go with OEM on a car you plan to keep for at least 2-3 more smog tests.

It all fit in my E24 pretty well.

IMG_0881.jpg

[TedBobo]

My 850i had no cats when I bought it. I ended up just getting a used set of cats from a 60k mile car that was wrecked. I verified the smog history of the donor car (you can do so for free here: http://www.bar.ca.gov/pubwebquery/ve...pubtstqry.aspx) and it had passed every time it was tested, so I figured it would be a good bet.

I would go with OEM on a car you plan to keep for at least 2-3 more smog tests.

What he said.

I did the same thing last year...bought a set of low-mile OEM cats from Walter (former owner of the super-charged 850 now residing in NorCal). Passed SMOG with flying colors. My old cats had about 155k on them and I passed the previous SMOG by a single point!

[cartoonz]

The Walker cats I posted above (#80832 is the one you want) are easier to mount than the magnaflows, imo.
That said, I have a pair of brand new Magnaflow cats in the garage sitting on a shelf that I'd sell for $125/ea, bought for a project I never did.

As for swapping in a used OEM set... its a crapshoot, at best. All of them are 20+yrs old at this point. Sure, they might work for a few years, but usually the cost vs aftermarket doesn't seem to pencil out.

[dragon850]

Do NOT use Magnaflow, you will regret it at the next smog test!
USE WALKER only!