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new ss slp headers and high flow cats p0420?

This is a discussion on new ss slp headers and high flow cats p0420? within the External Engine forums, part of the LSx Technical Help Section category; hey guys i just got a 01 SS today i am very stoked to be in the ls1 group now ...

  1. #1
    Junior Member bigjohn450's Avatar
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    ONYX BLACK
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    new ss slp headers and high flow cats p0420?

    hey guys i just got a 01 SS today i am very stoked to be in the ls1 group now
    but the guy i bought it from was from back east and dosent have emissions there and he put on a whole slp kit, lt's ,high flow cats and mufflers so i need to get it to pass smog here but it has the check engine light on with a p0420 code i havent been able to get under it yet to check all the o2's yet but from what ive been reading on here is that is a bad drivers side cat issue? but he said these are less than one year old. so i need to get the light to go off so i can get driving it. so im looking for some suggestions? ive searched tons of info but havent found any with my situation.
    thanks for any info in advance!
    this site rocks everyone is so knowlegable on here!

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    Member 98 Stang Killer's Avatar
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    congrads on car and welcome to the site not sure about the cat problem

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    Member slpdablueZ28's Avatar
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    im assuming thats the lean mixture code for one of the banks? happens to me every once in a while too. normally goes away though, usually goes off when i messed around with something in the car

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    Junior Member bigjohn450's Avatar
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    according to the guy i got it from its always on, i read the code and cleared it today and after about 10 miles of driving it came back on and it is the same code.

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    cutting and welding mark21742's Avatar
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    hugger orange
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    its your low catylst code, you can either leave it on or get the rear o2s tuned out. this happens alot of times when you run high flow cats. it wont hurt anything....but will fail emissions test with the light and code popping up

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    Member slpdablueZ28's Avatar
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    yeah thats weird it could be an o2 sensor. i changed mine the first time i got the code. kept getting it. but like i said its like a little gremlin that keeps popping up. itll come on then after driving a couple miles, or usually by then next time i start it up it goes away. the guys at autozone said that it could also be the injectors being dirty.

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    cutting and welding mark21742's Avatar
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    hugger orange
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    the high flow cats, by flowing better just dont do as good a job at cleaning the exhaust as a stock cat. lol what do you really want, more power, or cleaner exaust?..... i went for more power and hae cats at all

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    Junior Member bigjohn450's Avatar
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    yea im not worried about the light being on but it wont pass emissions with that code in the comp. so i need to get rid of it even if its temporarily. but it would be nice to have it gone. if i tune off the rear o2's would it still pass emissions?

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    cutting and welding mark21742's Avatar
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    hugger orange
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    Quote Originally Posted by bigjohn450 View Post
    if i tune off the rear o2's would it still pass emissions?
    yup, thats the best way to do it. if you use hp tuners, i know you uncheck ses/mil light and set it to (3 no error/no report). im not sure hotuse the other programs (ls1 edit, diablo) but im think they can do it too.

    if you dont plan on do alot more mods anytime soon id just take it to a tuner and have them take care of the light, tune the car, andtake your torque management out. you will notice a big difference

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    Junior Member bigjohn450's Avatar
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    ill have to look around for a local tuner, but my luck there wont be any in my neck of the woods

  11. #11
    cutting and welding mark21742's Avatar
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    Quote Originally Posted by bigjohn450 View Post
    ill have to look around for a local tuner, but my luck there wont be any in my neck of the woods
    lol yeah you are kinda out there in the middle of nowhere arent you. you could always buy the HPtuners program for $649, then charge a friend or two to tune theirs too. lots to learn but you can do alot with it

    or one more option is a mail order tune. you send your computer out express mail and they send it back in a few days....if your car can be down that long......frost on here does it that way and heard lots of good things about him

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    Member BlackSS1's Avatar
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    Quote Originally Posted by bigjohn450 View Post
    ill have to look around for a local tuner, but my luck there wont be any in my neck of the woods
    I had the same experience - after hiflow cats immediately it starts throwing codes. You need a mail order tune and it will turn off the light permanently.

    If you have OBD2 testing in Utah, even if you temporarily clear the codes with a handheld, your readiness monitors will not be ready and you will fail emissions until you tune those trouble codes out. Mail order to Frost is much cheaper than buying HP tuner software.

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    Junior Member bigjohn450's Avatar
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    thanks, maybe ill have to chat with him about the mail order way.
    also i was thinkng about maybe doing some o2 simmulators? just to get rid of the light and pass emissions. and do the tuning thing later when i get some cash.

  14. #14
    cutting and welding mark21742's Avatar
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    hugger orange
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    Quote Originally Posted by bigjohn450 View Post
    thanks, maybe ill have to chat with him about the mail order way.
    also i was thinkng about maybe doing some o2 simmulators? just to get rid of the light and pass emissions. and do the tuning thing later when i get some cash.
    I'd stay away from the simulators if I were you , I tried them....worked for about a week and they got hot as hell and burnt themselves out then started poping codes again

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