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Thread: e36 m3 Post-cat O2 sensor replacement question

  1. #1
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    e36 m3 Post-cat O2 sensor replacement question

    I was out on a long drive last week, and ended up with what I thought was an exhaust leak; but in actuality I lost one of my post cat O2 sensors.

    I was going to replace it, and found that the midpipe has an o2 sensor adapter that unthreaded. Is this adapter piece common, and does anyone know where I can find a replacement?

    Mike

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  2. #2
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    Our cars came without any type of adapter on them. Check to see if the O2 sensor without the "adapter" fits. If it does, those may be "non-foulers" which move the sensor out a bit so they're not in direct flow of the exhaust (supposed to extend life), and you can safely run without the non-fouler, or pick up new ones. Often found at local auto stores or online if you search for non-fouler.

    If the thread is a completely different size, then I'm not sure. Only guess would be they're SAE adapting to metric, or the wrong size altogether. Maybe someone else knows.
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  3. #3
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    You can remove the non foulers, they aren't doing anything good. Drive it and see if any codes come up. If you do get a catalyst code you should then replace both pre-cat sensors (not the post cat ones).

    - - - Updated - - -

    Use anti seize on the thread, don't get any on the sensor, torque to spec.
    Avoid Vogtland Suspensions! Rusted then failed!

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  5. #5
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    The OEM replacement sensors just thread right into the bungs. Nothing else required. Just torque to spec, and apply some anti-seize if you like (though I think the new ones I did a couple years back came with anti-seize tape or something on the threads). You should be able to find the exact part numbers over on realoem. I did all four of mine not too long ago and have had zero issues since (and an improvement in gas mileage).
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  6. #6
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    Also when you re-connect the rear sensors and if you get a code, I would start with a can of injector or complete fuel system cleaner like one of Royal Purple's products and see if that clears the code. Because it will help clean the cats.
    Avoid Vogtland Suspensions! Rusted then failed!

  7. #7
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    Thanks for the help guys. I thought it was a different thread because it didn't seem like the O2 sensor was threading into the midpipe, but it was just a difficult angle to get at. It was a non-fouler....I removed it and I appear to be code free.

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