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      06-03-2021, 04:35 PM   #6
bmwlover0725
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Drives: 2008 M3 Coupe
Join Date: Jun 2015
Location: Syracuse, NY

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Quote:
Originally Posted by dpaul View Post
Question 1) when did the O2 problems start relative to the hard start problem?

Question 2) who did the O2 sensor replacements? Was the joint between exhaust header and catalytic converter disturbed during that process?

Here's something you can do right now - get under the car and look very carefully at the joint between the exhaust headers and the catalytic converter for bank 1 (passenger side). See if there is any carbon residue or other signs that might be interpreted as a leak. If you're uncertain, compare it to the driver side where sensor function seems to be normal. It doesn't take much of a leak to cause a problem.

While you're under there, carefully inspect the condition of the wires and connector. Often you can't tell a thing but sometimes a problem is obvious.
One thing I also left out, I have no cats and a BPM tune. There are no leaks whatsoever after thoroughly checking though. My guess on wiring is that it's completely fine given that every sets fine at first until the O2 sensor goes bad.
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