catalyst system below threshold but no cat
 

I have a greddy catback exhaust and it has a resinator but no cat. would that be my o2?

Well not having any cat would put the CATalyst system below threshold. But the CAT back on and that CEL should go away. What did you think would happen once you removed the cat, the car does monitor things like that.

will not having a cat on hurt the engine?

No it will not effect your engine, it might be an issue noise wise with local police and if your state inspect cars.

oh, so i dont need to worry about the code? the CEL goes off every once in a while but comes back on later

Not having a cat causes you to lose backpressure .... mazda designed the renesis with this in mind and it recycles some of the exhaust gas back in the engine (The last part of the exhaust stroke, right before intake, some exhaust gas with unburned fuel gets sucked back in as the rotor is moving). This will cause you to run slightly leaner than stock, especially at WOT. However, there is such a large safety margin built into the fuel maps, that it is not really something to worry about, especially with long term fuel trims factored into the equation.

In the future, make sure you look into all of the effects of a mod before installing it


this code is simply telling you that your cat is bad ... since you do not have a cat this makes perfect sense

Where did you get this crap from ;) There is no overlap in a Renesis........And the rest is well....made up :)