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Unread 07-10-2007, 08:49 PM   #7

Name: minnie
Title: United Newb
Status: Offline
Join Date: May 2007
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Your Ride: m3
Hi everyone,
I live near San Diego and my 1998 Z3 CEL went on because of a low catalytic converter efficiency. Finding information about what you can and cannot do in California when this happen it has been quite a challenge. There’s a lot of confusion and incorrect informations out there so here’s what I learned on this project.
1) Yes, California is dictating standard on emissions (thanks God!!!!)
2) No, you don't need to buy the original BMW
3) Be very careful of what you buy on the Internet
The CARB (California Air Pollution Board) dictate standards about various devices that affect emissions; one of them is the catalytic converter.
CARB said that no catalytic converter other then the OE can be sold, UNLESS it explicitly complies with the regulation and it has been tested to work with OBDII. If so CARG grant the producer of such converter with an exemption.
Quote from the CARB web site
“Exempted parts are add-on or modified parts that have undergone an ARB engineering evaluation. If the part or modification is shown to not increase vehicle emissions, it is granted an exemption to emission control system anti-tampering laws. This exemption is called an Executive Order (EO) and allows the modification to be installed on specific emission controlled vehicles. Every Executive Order part or modification has an assigned number that can be verified by Smog Check stations, BAR Referee stations, or by the ARB.”
There's only 1 company for our BMW other then the OE that is legal: it’s called Miller Catalyzer Corp ( You can check their authorization here (
The catalytic converter for my 1998 Z3 1.9 will cost me $650 + $100 core I'll get back once I turn in my old cat. I believe the OE from BMW was probably somewhere in the upper $1,500.
All Miller converters come with the required 5 years/50K miles warranty.
Only Miller and the OE from the BMW dealer are legal: everything else is NOT legal in California.
There's actually a third option: there's a website called that sells converters legal in California. All they do is weld the universal Miller converter on the original pipes.
If you don't want to blow you new converter I would suggest changing both O2 sensors (they are responsible of the air-fuel leannes/richnes)
That's it. End of the story: is ether Miller or the OE BMW...

My only question based from your number 2 experience is, why not using original bmw catalytic converter since it is more advisable?

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