Pls help. I have the aftermarket headers and no catalytic converters. The computer/ECU is not getting the exhaust data that it wants and is forcing the engine to run pretty rich. Is there any way to bypass this or am i looking at getting a new ECU just so I can program it to run correctly again? Thanks. Rich

what makes you think your running rich? I called NExtGen about that and you may not be running rich but rather what you smell and your mufflers turning black is just the crap that the catalitic convertor should be catching. But since you don't have one its all coming out.

edit: also just as long as the top two o2 sensors are plugged in you are fine. the bottom two are just for emissions and don't have anything to do with the air/fuel mixture.

Yeah, I would also like to know what makes you think it is running rich. I doubt very much that removing the cats would cause this.

possible, but doubtful, there have been way to many peeps to install hneaders, and none have been running any Richer than the stock hyundai richness, which may be the proglem you are facing, My suggestion, Apexi SAFC or MAFterburnewr from TC @ next generation Motorsports

what makes you think your running rich? I called NExtGen about that and you may not be running rich but rather what you smell and your mufflers turning black is just the crap that the catalitic convertor should be catching. But since you don't have one its all coming out.

edit: also just as long as the top two o2 sensors are plugged in you are fine. the bottom two are just for emissions and don't have anything to do with the air/fuel mixture.
Can you give us some more info? I don't understand what the bottom sensors do for emissions without affecting the air/fuel mix.

The top sensors are what the ecu uses as a feed-back mechanism to adjust the A/F mix for anything but wide-open throtle. The ecu uses the bottom two sensors to check how well the manifold cats are working. It does not use this information as a feed-back mechanism for the A/F mix. So your engine is not running "rich" because the fuel injectors still have the same duty cyle as they did before your headers. The ecu uses the first set of injectors to keep the same fuel mix. As long as you have the first set of O2 sensors in, the ecu really doesn't know the difference of whether you have headers or not.

The first set of O2 sensors reads the exhaust and tell the ECU to adjust the mixture if needed. The second o2's simply tell the ECU whather the cats are still working properly or not. Since you no longer have the cats the rear O2 thinks that the cat has gone bad.

Mine don't think didly cause I have them in and they don't read any CELs.

Had all 4 of mine in for a month with no cells but i still removed them anyway. Still no cells. I agree with the statement about no cats so yours smelling what they use to burn up. Tibs run rich anyway so not to worry.

i just cleaned my mufflers yesterday. after two months of not having any cats they were black, completly and utterly black. got a cat put on thursday so i cleaned them yesterday and they are so shiny. it really makes a diffference.

Thanks Dingleweed and AdRock. After reading you replies I went to the webtech site to try to figure out how that could work. I didn't realize there are 2 catalytic converters in the exhaust, so now it makes perfect sense. That made me think of another question. When people talk about catback systems, are they talking about replacing the exhaust after the manifold converter or the one downstream?

okay.. so what would happen if you had the wrong 02 sensors plugged into the headers? Like didn't plug in the top one... and used the bottom ones instead?

okay.. so what would happen if you had the wrong 02 sensors plugged into the headers? Like didn't plug in the top one... and used the bottom ones instead?

That probably wouldnt be good, because it would try to sense an AF ratio and not get anything


And JS, they are referring to the downstream cat

i just cleaned my mufflers yesterday. after two months of not having any cats they were black, completly and utterly black. got a cat put on thursday so i cleaned them yesterday and they are so shiny. it really makes a diffference.

What headers and exhaust do you have?They started emissions in my state this year and i preferr either keeping my cats,or buying a hi-flow cat.Anyone know if there are any fitment/performance issues with using a cat instead of the race pipe with nexgen's headers?

What headers and exhaust do you have?They started emissions in my state this year and i preferr either keeping my cats,or buying a hi-flow cat.Anyone know if there are any fitment/performance issues with using a cat instead of the race pipe with nexgen's headers?

I have the NextGen headers and the KORE exhaust. The cat that I bought was 14in long and the guy at the shop had to add about 2in on to it to make it fit in place of the race cat. Performance wise, theres probably a small decrease but it got rid of a buzzing sound during acceleration and of course the whole thing with emissions.

And JS, they are referring to the downstream catThank you Ron

Had all 4 O2 sensors in for 2 months, no issues.

Thanks for the input guys. Really appreciate it. Sorry it took so long to respond, been in Jersey for a week. Thanks again, Rich.


Edit: Oh and by the way, I am putting the catalytic converter back into my exhaust setup. I have the SSautochrome headers, (Hi-Flow on the way) 40 series flowmaster, 2.25" all the way back, and Magnaflow stainless steel tips. Sounds more like a muscle car than an import, a loud muscle car.