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Discussion Starter #1 (Edited)
Hey guys I had a set of headers installed recently and everything seems to be running great so far.

My question is in regards to the post cat O2 sensors... I'm throwing a CEL which I knew would happen, and I'm going to have the car tuned and the post cat sensors re-programmed so that they are fooled into thinking everything is ok (by raising the acceptable level of air vs emmisions) It is my understanding this will keep the CEL off. Is there anything else I need to be aware of? Will this have any negative effect on the car? Anything else I need to do?

I've read the entire header thread prior to buying the headers but I know that my mechanical knowledge is sub par so any help is appreciated. Also emissions testing is not a concern as my new address is just past the "border" of the emissions testing region and is no longer required. Basically just want to know my car is performing at optimal levels and not undergoing any undue stress because of something I missed or didn't properly comprehend.

Thanks
Cheers
 

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When Air/Fuel mixture ratios are computed by the O2 sensor to check if your car is running "optimum" they simply gauge if the car is running lean or rich. OEM headers have the ratio programmed. Since you are going to reprogram to bypass the light error, the only way you can answer your question is to go to an emission center and have them check your exhaust and tell you your numbers. Obviously if they state it is rich or lean, your mileage will not be as good as it was/could have been with OEM headers.

In Michigan, they have never had emission testing and some of those 60-70's American Muscle cars run so poorly you can faint with the smell of gas and lack of tuning. Its only going to affect your mileage since the combustion is already done and its only exhaust that needs to exit now.

Once you get the emission testing numbers, you will know if your car is running rich or lean, then you can check your mileage.
 

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Discussion Starter #3
Oh ok just wasn't sure if the engine would be put under stress from "starving" for fuel or "flooded" with fuel.
My mileage has improved if anything so I guess so far everything's ok. I just didn't now if messing with the post cat sensors would throw anything off once the values were tweaked.
 

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Well, its not to say that your engine is not running optimum. You should really get an emission testing done to verify that. Its all or nothing with those test results and you can see for yourself. If you see an extreme tilt to lean or rich your going to have to make changes. I don't think anyone can answer as to if your engine is suffering with your install, only way is to get it tested, worth the money!
 

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Post cat O2 sensors just measure whether or not the converters are working they have nothing to do with how the engine runs. Its only the front two that really matter. To ensure this get the code read (autozone will work for this) and it should read somewhere in the neighborhood of some catalytic efficiency code or maybe bank 1&2 sensor 2 rich codes

EDIT: On a side note after confirming what i said you can try to space you post o2 sensors to remove the code, will cost around $10 for parts. The DIY is somewhere on this site if you haven't found it yet.
 

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Discussion Starter #6
Post cat O2 sensors just measure whether or not the converters are working they have nothing to do with how the engine runs. Its only the front two that really matter. To ensure this get the code read (autozone will work for this) and it should read somewhere in the neighborhood of some catalytic efficiency code or maybe bank 1&2 sensor 2 rich codes
Thanks now that you mentioned it I remember reading that the post cat sensors only measures cat efficiency. I just wasn't sure if without the cats and the sensors reading abnormally high output exhaust levels if the engine would try to compensate somehow.
 

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Thanks now that you mentioned it I remember reading that the post cat sensors only measures cat efficiency. I just wasn't sure if without the cats and the sensors reading abnormally high output exhaust levels if the engine would try to compensate somehow.
No problem, always enjoy helping other car people out.
 

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I also just installed cat-less headers and while throwing a CEL I got 41mpg on a road trip from missouri to colorado. Thats running 70mph almost the whole way, easing into the throttle when needed to pass etc.
 
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