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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Thu, Sep-30-2010, 02:05:38 AM   #1
FLBMWM3
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Default Post cat O2

I had a shop install my headers. Now I live in a state that enforces emissions testing so I have installed cats in the section 1 mid pipe.

My questions is how do I determine which O2 sensors are the post cat sensors so I can move them to after the cats?

Thank you
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Old Thu, Sep-30-2010, 11:51:17 AM   #2
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Are your precat O2's not in place? If so, then the two leftover are your post cat O2's.
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Old Fri, Oct-01-2010, 02:17:20 AM   #3
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Right now on the headers all four bungs have O2 sensors. I would assume that the two highest bungs are the pre cat and the two lower bungs are the post O2.

I didn't know if there was a way to pop off the engine cover and check the wires to see which was post or pre, or is I could see which o2s were the longest and that may tell me?
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Old Fri, Oct-01-2010, 02:27:18 AM   #4
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Quote:
Originally Posted by FLBMWM3 View Post
Right now on the headers all four bungs have O2 sensors. I would assume that the two highest bungs are the pre cat and the two lower bungs are the post O2.

I didn't know if there was a way to pop off the engine cover and check the wires to see which was post or pre, or is I could see which o2s were the longest and that may tell me?
There is a difference, I believe they wire colors are different front to back. I read it somewhere on the forum. I did a quick search but I will check all data tomorrow at work.
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Discussing Post cat O2 in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)