I own a 2004 RX-8 MT and recently the CEL came on. I ran a diagnostic on it and came back with 3 Cat System errors. In addition I had a severe decrease in power in higher RPM's. It feels as if the second set of injectors are not kicking on at 3750 RPMs like they are supposed to in addition to the engine feeling like it is suffocating at certain RPMs. The engine is fine and in excellent working order, but I can't seem to get it to redline for the life of me. I read that in some cases the cat was the major factor for other people having decreased performance and fixing the cat through various means solved a lot of their problems. I took my car out last night and ran it at operating temperature for about 20 minutes to find out if there were some kind of unnecessary back pressure due to leaks or blockages which usually results in the cat glowing orand and when I got oiut to check the cat it was in fact glowing orange. I'm going into a muffler shop this weekend to have them VISUALLY inspect the cat and see if that is malfunctioning. I'm not sure if the cat is the reason for the decreased performance, but I was told putting a down pipe or straight pipe (whatever you prefer to call it) would be one way to eliminate this problem. Is that true? Or even an effective way to deal with the problem? I'm relatively new to the rotary scene and the components relation to their sensitive performance so any feedback just short of "you're an idiot" would be greatly appreciated.

 

My 04 had it's cat replaced 3 times in the first year. This was before numerous computer flashes and a engine replacement. I haven't had a problem since.
A bad cat will cause a reduction in performance and not allow enough exhaust flow to reach redline. There was never any visual indication, on my car, that there was a problem.
Even if your car warrenty is up, you should still be good with the emissions warrenty mandated by the US goverment. Get the cat replaced.

 

Take the car to the dealer - the CAT (and it sounds pretty much like what happened to me - I got a new CAT !and! as you are getting CAT CELs anyway) is a warranty item w/free replacment to 100K miles or so I believe.

 

Cat. And probably coils, too.

 

It has nothing to do with *rotary or not*

US laws required that auto companies to cover emission related stuff for 120K miles (I think, maybe 100, not 100% sure)

and next time, it will be better and faster to do a search, your problem has been answered like 10000000000000000000000000000000000000000 times.