My check engine light in my '03 Rubicon has been on for a while now. I have had it to the dealer and they keep saying it is the O2 sensor and replacing it and about two days later the light is back on. I had Auto Zone do a diagnostic test and they said it showed the O2 sensor, air flow sensor, and a missfire in the 3rd cylinder. It seems to be running fine. Any idea on what is really going on? I have a K&N cold intake air filter, 68mm borred throttle body and spacer, 190 low-temp. thermostate, a stage two jet performance chip, and a Banks Power header and cat back exhaust. I also notice I have dust collecting around the throttle body spacer where the gaskets are.  

You're messing with fire with all the intake stuff you have changed. None of it does anything good for you. Just puts money into other people's wallet.

All these changes makes it hard for the computer to make good decisions about fuel and ignition management. When it's not right it overheats the o2 sensors and the cats, eventually breaking down the catalyst.

There are two o2 sensors before the two mini cats and two after. They work in harmony to determine if the cats are effective. If the post o2 sensors read the same as the pre o2 sensors, then it is determined that the cats are not working. Since the o2 sensors are on different cylinder banks, they can also make a determination as to misfire.

Replacing the o2 sensors proves that nothing is wrong with them, and the problem lies elsewhere.

The engine temp is an important input to the computer. Why would you mess with that?

Open element filters take in more dust and heat than the stock element in an air box. It is this underhood heat that makes them such a joke as to improved performance. In the lab they produce MAYBE 5 hp. But in the real world, because of the heat, they are a waste of money. And even if it did get 5 hp real world. So what. You can't feel it and it won't increase your fuel economy because the 5 hp is acheived at wide open throttle. And WOT is not good for fuel economy.

Take off the Jet chip, reset the computer and see what
happens.  

Private message to ftgiles from flimmatt    Posted: 07/14/08 05:43 PM

JUST WANTED TO SAY THANKS FOR THE REPLY YOU GAVE TO THE 03 RUBICON .I HAD DONE THE SAME EXACT MODS TO MY 02 SPORT AND WAS HAVING THE SAME PROBLEMS.I couldn't fiqure out how to fix the problem with the o2 sensor and nobody else could help either. I tried your suggestion about the chip and my problem went away.         THANKS FOR THE HELP. MATT