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Headers/cats emissions question

This is a discussion on Headers/cats emissions question within the External Engine forums, part of the LSx Technical Help Section category; Bear with me as this might be long.... My car has been rejected by the Indiana emission test for the ...

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    Headers/cats emissions question

    Bear with me as this might be long.... My car has been rejected by the Indiana emission test for the last 3 tries with this "Incomplete monitor: catalyst" then all of a sudden right after the last test earlier today my Check Engine light came on. Of course it's the P0420 code for converter efficiency below threshold. As I see converters aren't cheap for my car, I was thinking of finally getting around to headers/y-pipe with no converters. Now, if I go with this setup with o2 sims this will pass the emission test, right? It won't show "Incomplete" again? Just wanna make sure I'm on the right path here

    Also I just put a Dynomax racebullet catback on my car for the stock exhaust, will this work with the y-pipe that comes with the headers? Thanks for any help with this.
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    She Moderator KahanaReef's Avatar
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    I'm not sure where you are located, but some states require you keep them and LT headers aren't legal like here in CA.

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    I'm in Indiana and as far as legal, I'm not sure either but I do know they don't do the "use a mirror to see a cat/s" thing like they do for older cars, only the gas cap check and computer.

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    I'm from Indiana and they do not do a visual inspection. Just OBDII plug in. I do not have catalytic converters and I have LT's installed and pass without issue.
    It's on jackstands.

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    You may just have a bad O2 sender. Any drop in mileage or driveability issues?

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    Nothing noticeable, I do have autotap as well as a predator programmer that'll give me voltages on them, what should I look for as far as knowing if I have a bad one?

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    I just checked voltages with my predator and here's what I got:
    Idle 2000rpm
    Short Term Bank 1 .78-1.56 0-4.69
    Long Term Bank 1 3.91 14.06
    Short Term Bank 2 .78-1.56 0-4.69
    Long Term Bank 2 3.91 17.97

    What do you think?

    Sorry, can't get the columns to line up.

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    You would have to look at Bank 1, Sensor 2, which is the rear O2 sender (after the cat, or on the cat -- I cannot recall) on the driver side. The front sensors are what help control fueling. The rear sensors simply tell the PCM if the cats are functioning correctly. You could also swap the rear O2 senders from side to side and see if the problem moves with the sensor, or if it stays on the driver side.

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    Quote Originally Posted by pajeff02 View Post
    You would have to look at Bank 1, Sensor 2, which is the rear O2 sender (after the cat, or on the cat -- I cannot recall) on the driver side. The front sensors are what help control fueling. The rear sensors simply tell the PCM if the cats are functioning correctly. You could also swap the rear O2 senders from side to side and see if the problem moves with the sensor, or if it stays on the driver side.
    Sorry for the late reply... was out of town. I'm going to try swapping them and see what happens. Thanks for the help with it.

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    02 simms will work. I used them back like 12 years ago. I had one of em go bad tho and had to get another. If you can find a tuner it's worth it to have him tune out all the emissions codes.

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    Will sims tell the computer they are "ready" That's the problem I'm having. Or if they were tuned out, will it show "ready"

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    Quote Originally Posted by 35th-ANV-SS View Post
    I'm from Indiana and they do not do a visual inspection. Just OBDII plug in. I do not have catalytic converters and I have LT's installed and pass without issue.
    Do your 02 sensors status show "ready" or "complete"? My autotap still shows the catalyst as incomplete.

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    Senior Member INMY01TA's Avatar
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    Quote Originally Posted by Dano 00TA View Post
    Will sims tell the computer they are "ready" That's the problem I'm having. Or if they were tuned out, will it show "ready"
    Yes.

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    I'm assuming yes as I have never had any issues with passing emissions. My rear O2 sensors have been tuned out for a long time now.

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    Well, I ordered a set of TSP 1 7/8 headers/ory and of course after they shipped I remembered about the A.I.R hookup which as my luck runs, have none. Might have to have these removed also now or see if I can find bungs to have them welded on.

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    Ditch the secondary air -- it's easy: Secondary Air: Diagnosing and Removal

    You'll want a tune anyway with the new headers, so have the secondary air code shut off so you do not end up with the SES lit up.

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    Thanks for the help with this! I'm gonna probably invest in HP Tuners now so I can get this all done.

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    HP tuners is something you really don't wanna mess with unless you know what you know what your doing. I would just get a mail order frost tune. It's cheaper anyway.

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    Quote Originally Posted by RONS98TA View Post
    I would just get a mail order frost tune. It's cheaper anyway.
    Yep!

    Pretty foolproof. I have had zero issues with my Frost tune and
    coincidentally i too have the TSP LT's.

    Bit of a story there about fitment... but all good if you get the correct
    headers!!!


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    Yeah, might just go with a frost tune then, was just thinking of more mods later and the ability to tune again w/o having to need another mail tune. Thanks

    I have been reading some horror stories with these headers and read some went pretty easy, hopefully mines the later.

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