Catalytic Converter replacement

[cel0202]

Hi folks,


It looks like both my catalytic converters are in need of replacement. It has been suggested that the entire OEM system is not worth the money, and that an after market pair for $300-400/ea with at least 2 yr warranty, some splicing and welding via a trusty muffler shop, would be wiser. Thoughts?


I’ve read through some older catalytic converter specific posts here on the E31 forum and many have spoken about getting rid of them completely and/or replacing the system with Magnaflows. Being in California, I would assume deleting the cats completely would result in failed smog tests. Is this correct? And with regard to Magnaflows, I’m at that age where I prefer a quiet ride.


My question is.. are there any specific after market / third party catalytic converters that is recommended? Or would any “universal” cats work? Or are there any recommended Magnaflow systems that run as quietly as a factory exhaust system that will pass smog tests in lieu of the splicing and welding option?


Much thanks as always.


CEL

[rjbaren]

I removed my converters on my 95. In IL we don't test 95 and older cars. The car ran the same and it was not any louder. The down side was the smell. My wife made keep the garage door open for 15 minutes after I drove the car. I just had a single cat installed with two in and two out. The performance is still the same and there is no smell.

[m6bigdog]

FWIW,
If your emissions test show excess NOX, you might want to replace the O2 sensors before you go to all the expense of replacing the CATs. The M60/M62 is notorious for running lean from the O2 sensors output drifting above 60k miles and the leaner mixture prevents the CATs for converting the NOX. Yep, the O2 sensor voltage will look perfectly normal but the Air Fuel Ratio has drifted leaner than normal hence the CATs do not work normally.

[cel0202]

Fortunately I passed my last smog test in Aug 2014 (and 2012, '10 and '08 with no issues) and am not due for another one until Aug 2016. It's only recently that my catalytic converters failed. I also replaced my O2 sensors 6 years ago (seems just like yesterday) and have driven approximately 23,000 miles since then.

My goal at this point is to weigh out my options regarding the failed cats:

- replace with after-market brand rather than OEM. If so, what brand and model? And is cutting old and splicing new into the existing pipes common or even recommended with the E31?

or

- replace entire system w/ Magnaflows? If so, I would want "quiet" ones that will not cause a fail during my next emissions test in 2016.

Cheers,
CEL

[wokke]

I recently had a customer with an extremly nice '99 840Ci with broken (yes, phyically broken) ceramic internals in the cat converters.
He didn't want any after market stuff welded in as he wants his car to look original. So I opened the original cats and emptied them entirely.
Then I took two Magnaflow cats, cut them open, removed the monoliths and inserted them into the original cat housings.
Has been a bit of work but now it looks original again and will pass smog tests even easier than before because of newer cat technology.
If needed I can suppyl the exact Magnaflow cat model plus more info on how to do the conversion.

[thelongeride]

Now that's commitment.

[mattsimis]

Ive been catless for years on my CSi but was getting sick of the smell and some smoke puffing. Put in some universal cats, quite small and high flow (they were expensive, like $90 each) and they work fine. I put them in with exhaust clamps though the piping was only 1/2mm larger than the pipe I was sleeving it over so the clamps are probably unnecessary. Sounds better (more low down rumble) and runs better (more responsive from pickup and smoother). I have Dbilas Cams too which IMO were pushing it over the edge and the cats helped the ECU get back in control fueling wise.

[tvjake2]

- replace with after-market brand rather than OEM. If so, what brand and model? I replaced my cats with aftermarket units for $200 each and they have worked well for 2 years. I'll know more at the next smog check.

or

- replace entire system w/ Magnaflows? If so, I would want "quiet" ones that will not cause a fail during my next emissions test in 2016.
My understanding is that the Magnaflow cats will not add extra sound and are a good replacement.

[72tpik5]

Magnaflow and plenty of others make aftermarket cats. Have a look on Ebay.

[cel0202]

This is amazing and your customer is definitely a committed owner. I'm curious if re-housing an after-market cat into a factory housing is acceptable in California. FYI, here is a list of approved cats for California: https://www.magnaflow.com/02catalyti...&splityear=PRE

I recently had a customer with an extremly nice '99 840Ci with broken (yes, phyically broken) ceramic internals in the cat converters.
He didn't want any after market stuff welded in as he wants his car to look original. So I opened the original cats and emptied them entirely.
Then I took two Magnaflow cats, cut them open, removed the monoliths and inserted them into the original cat housings.
Has been a bit of work but now it looks original again and will pass smog tests even easier than before because of newer cat technology.
If needed I can suppyl the exact Magnaflow cat model plus more info on how to do the conversion.

Were your old cats cut and new cats welded in to the existing pipes?

- replace with after-market brand rather than OEM. If so, what brand and model? I replaced my cats with aftermarket units for $200 each and they have worked well for 2 years. I'll know more at the next smog check.

or

- replace entire system w/ Magnaflows? If so, I would want "quiet" ones that will not cause a fail during my next emissions test in 2016.
My understanding is that the Magnaflow cats will not add extra sound and are a good replacement.

[rockytt]

I'm curious if re-housing an after-market cat into a factory housing is acceptable in California

Can't imagine that it would be - there's no way to pass a visual inspection with such a setup...

[olinjohnston]

Can't imagine that it would be - there's no way to pass a visual inspection with such a setup...

They don't look under the car, just at the EGR stuff and air intake...and if it were in a factory housing, how could they tell anyway?

[rockytt]

I hope I stand corrected!

[olinjohnston]

I hope I stand corrected!

I "passed" the visual inspection three times at two test-only stations with a freakin' superchager, but they did still look at the vacuum lines and EGR stuff...ha

[rharris99]

I haven't been as lucky...at a Star certified station 2 years ago when I was getting a smog check they pulled out the mirror on me to check for the "cat stamp" on my cats.

My registration is due next month so we'll see if they do it again.

[tvjake2]

I haven't been as lucky...at a Star certified station 2 years ago when I was getting a smog check they pulled out the mirror on me to check for the "cat stamp" on my cats.

My registration is due next month so we'll see if they do it again.

I've never had anyone look under the car for a smog inspection.

[72tpik5]

God bless the Midwest. Smog inspection? What's that? ��

[TedBobo]

I haven't been as lucky...My registration is due next month so we'll see if they do it again.

I'm up for Smog in August.....passed two years ago by a single point! Not looking forward to this years results. At the last test the tech said the cats were the culprit. Heidi only has 155k on her.

[rharris99]

I'm up for Smog in August.....passed two years ago by a single point! Not looking forward to this years results. At the last test the tech said the cats were the culprit. Heidi only has 155k on her.

I replaced my cats in 2011 and I only had 4K on the cats when I failed smog in 2013. They said the cats were the problem again so I got new cats and barely passed. I'm going to try the Seafoam that seems to work for everyone and hopefully that will make the difference.

Mangaflow will probably give me a hard time again if I say their cats are bad after 4K again.

[Timm]

I replaced my cats in 2011 and I only had 4K on the cats when I failed smog in 2013. They said the cats were the problem again so I got new cats and barely passed. I'm going to try the Seafoam that seems to work for everyone and hopefully that will make the difference.

Mangaflow will probably give me a hard time again if I say their cats are bad after 4K again.

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

[olinjohnston]

I replaced my cats in 2011 and I only had 4K on the cats when I failed smog in 2013. They said the cats were the problem again so I got new cats and barely passed. I'm going to try the Seafoam that seems to work for everyone and hopefully that will make the difference.

Mangaflow will probably give me a hard time again if I say their cats are bad after 4K again.

When my 840 failed smog, I was told the (original) cats were bad too, but I wasn't buying it, so I just did the test again, but revved up the motor and made sure they were as HOT as possible after driving 30-40 minutes before the test - passed with flying colors. Did not do anything else...

[toomanyparts]

When my 840 failed smog, I was told the (original) cats were bad too, but I wasn't buying it, so I just did the test again, but revved up the motor and made sure they were as HOT as possible after driving 30-40 minutes before the test - passed with flying colors. Did not do anything else...

The correct way to pass a smog test.

[TedBobo]

When my 840 failed smog, I was told the (original) cats were bad too, but I wasn't buying it, so I just did the test again, but revved up the motor and made sure they were as HOT as possible after driving 30-40 minutes before the test - passed with flying colors. Did not do anything else...

I did the exact same thing for my test and still only passed by a single point. I damn near drove to San Diego & back so I know the "cats" were good & hot! Can you get me a set of "loaner" cats?

[rharris99]

When my 840 failed smog, I was told the (original) cats were bad too, but I wasn't buying it, so I just did the test again, but revved up the motor and made sure they were as HOT as possible after driving 30-40 minutes before the test - passed with flying colors. Did not do anything else...

I tried that too...drove from Culver City to Anaheim and back and still failed... It will probably fail again so that's why I'm going to try the Seafoam and then make a long drive before testing.

- - - Updated - - -

God bless the Midwest. Smog inspection? What's that? ��

Every 2 years after the vehicle turns 6 (or transfer ownership) you have to get an emissions test (AKA Smog Test) to keep your registration current. It's basically a California scam to get more money from vehicle owners as we just in LA County alone have more cars than each state (except for Florida, Texas and NY). The only difference between the cats they sell in California and the other 49 states is there is a certification stamp on the cats (which can be seen if the smog station breaks out the mirror)

I must say that I think it has helped because when I was a kid a remember looking towards Downtown LA it used to be a orange haze on warm days...now its just a haze.

...this is probably more that you wanted to know about this.

[olinjohnston]

I tried that too...drove from Culver City to Anaheim and back and still failed... It will probably fail again so that's why I'm going to try the Seafoam and then make a long drive before testing.

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.