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420/430 code after header install

This is a discussion on 420/430 code after header install within the External Engine forums, part of the LSx Technical Help Section category; I just installed a set of MAC mid length headers with a catted Y-pipe and my check engine light came ...

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    420/430 code after header install

    I just installed a set of MAC mid length headers with a catted Y-pipe and my check engine light came on. I went to Autozone to have it scanned and it read the P0420 and P0430. The reason I put new headers on was b/c I pulled a 420 code earlier so I figured I had a bad cat. My passenger side O2 should be the same one I used before which wasn't throwing any codes, but I changed out the drivers side with one that came with the y-pipe ( I bought the header/y-pipe used with less than 1000 miles on it and it came with 2 02 sensors in it).

    Any ideas?
    '99 Trans Am WS6
    MAC mid length headers, catted y-pipe, Flowmaster muffler, cut out, FRA

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    Slow'er'Ass Mr. Luos's Avatar
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    Get them tuned out.


    The problem is that while a high flow cat works, it doesn't work 'well' enough to keep the codes from popping up.

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    Does it hurt anything by driving the car like this? I haven't noticed my fuel economy being any worse, but this is also just a weekend car.

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    Slow'er'Ass Mr. Luos's Avatar
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    Nope. Hurts nothing.

    The ONLY thing those rear O2's do is compare levels to the fronts. To determine if the cats are working 'properly.'
    The fronts assist in the control of the A/F.

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    Quick question. I've gotten my pacesetter headers ordered along with the ORY. The headers will have a place for the O2 sensor? Do I have to go to a dyno shop to get the rears tuned out, or can I get a handheld unit to tune them out?

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    Quote Originally Posted by Speed_kills_WS6 View Post
    Quick question. I've gotten my pacesetter headers ordered along with the ORY. The headers will have a place for the O2 sensor? Do I have to go to a dyno shop to get the rears tuned out, or can I get a handheld unit to tune them out?
    The headers will have a place for the 02 sensor. I don't think any handhelds can tune out the rear codes, you need HPtuners, LS1edit or something along those lines to turn off the rear codes.
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    The Bandit Wesman's Avatar
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    Quote Originally Posted by Speed_kills_WS6 View Post
    Quick question. I've gotten my pacesetter headers ordered along with the ORY. The headers will have a place for the O2 sensor? Do I have to go to a dyno shop to get the rears tuned out, or can I get a handheld unit to tune them out?
    Yes, the headers will have primary O2 bungs in them.

    You can delete the codes either way. Some handhelds can do it, but you are better off just having a tuning shop do it so they can tune the car and delete the codes all in one shot.

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    Member Speed_kills_WS6's Avatar
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    Thanks for the info guys. Just hope I'll get ample performance out of it.

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