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  1. #1
    FEP Power Member fgross2006's Avatar
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    Default placement of downstream O2 on 96 Yukon custom exhaust

    Does anyone know if there is a standard length for placing the bung hole for the after cat O2 sensor in a custom pipe build?

    In a stock set up, the replacement Cats would come with pipe and bung holes already where they should be. But I had custom 2 1/2 pipe bending done to my 96 Yukon a few years back, from the exhaust manifolds to the tail pipe.

    I never had codes before but right after having the custom job done I started getting bank 2 sensor 2 codes. Sometimes it says too rich, sometimes it says catalyst not functioning.

    I had custom piping, two brand new high performance magnaflow cats and a hi-perf magnaflow muffler.

    I changed the bank 2 sensor 2 O2 last week and so far no new codes, but that doesn't mean anything yet. This random code issue pops up sometimes 3 weeks later, sometimes 6 weeks later. Until I stop seeing it for maybe 2 months I wont be satisfied. I ordered 3 more O2's just for good measure and I hope to have them in this weekend.

    But I did notice that the downstream O2 on bank 1 is further away from the cat than the downstream O2 on bank 2.
    I assume the crossmember got in the way so it was a choice of 4 inches after the cat or 16 inches after the cat. Is there a standard distance before/after the cats for optimal O2 sensor readings?

  2. #2

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    The after cat O2s are only there to prove the cats are working. They aren't used to control mixture refinement. Basically just to meet emissions standards.
    I don't think the placement would matter. This far down the exhaust, the temps are way lower than up by the exhaust manifolds.
    I know you bought a name brand cat, but the easiest answer is one isn't as good as the other. That's why the sensor is setting codes
    If the o2 wiring had to be modified from stock, maybe something is wrong there
    Also, maybe consider an obd2 scanner that shows live data. So when the code reappears, you can look at things in real time
    I know you can buy/ make, a plug in way to remove the obd2 mustang's 2nd o2 sensors. maybe there's a similar thing for chevy.

  3. #3
    FEP Power Member fgross2006's Avatar
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    Default

    Quote Originally Posted by boboli View Post
    The after cat O2s are only there to prove the cats are working. They aren't used to control mixture refinement. Basically just to meet emissions standards.
    I don't think the placement would matter. This far down the exhaust, the temps are way lower than up by the exhaust manifolds.
    I know you bought a name brand cat, but the easiest answer is one isn't as good as the other. That's why the sensor is setting codes
    If the o2 wiring had to be modified from stock, maybe something is wrong there
    Also, maybe consider an obd2 scanner that shows live data. So when the code reappears, you can look at things in real time
    I know you can buy/ make, a plug in way to remove the obd2 mustang's 2nd o2 sensors. maybe there's a similar thing for chevy.
    Funny you should reply now.

    Last weekend I changed all my O2 sensors with all AC Delco's As soon as I did that I started getting thick white smoke and it stinks of unburnt gas. Stupid me, I threw away all but one of the originals and all the boxes they came in.

    I have a OBD2 scanner and pulled up a real time reading and saw 3 of the O2's seem normal with voltage but bank 1 sensor 2 has whacky voltage readings. I ordered 1 upstream O2 to try to replace it. I'm hoping thats the issue because I cant leave it like this.

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