Actually i think i've found the solution to cat failures on the RX-8. I recently experienced the glowing 02 sensor, thinking it might be clogged catalytic converter, plugs, coils etc, also had the "marbles in a can sound". It turns out it was the type of gasoline i was using. Here in Europe its normal to fill with 95 octane, which is also what is recommended for the RX-8. After i switchted to 98 octane from Shell, the cat stopped glowing!! I tried to abuse the care many times, but cat still not glowing . Try some proper fuel, i bet it fixes the issue! Is the RX-8 ment to be fuelled with 98 octane? I think so. Feel like suing Mazda right now.

Can anyone else confirm this?

 

I bought my car is the US, in the US 91(95 for EU) and above is recommended and you can use a 87
which is regular with a decrease in performance, in EU unit it might be 92 or something.
The MIAC sounds like you are experiencing engine knock, or missing the heater core orifice.
The most significant difference between a 95 and a 98 is the octane level, 98 is more resistant to detonation than a 95. You might be experiencing engine knock that the knock sensor is pulling timing.
if I am correct, retardation of ignition timing will raise EGT and that’s why your cat is glowing.
But since our car will take 95 without any problem, is it bad fuel? Running super lean+detonation?

 

I dont have MAIC on 98 octane, like i said all problems went away, including powerloss after fuelling with Shell EU 98. Can someone with same issue try higher octane fuel(US 94), thanks!

Yes US 92 is EU 96. US 94 would be EU 98.

 

Like Brettus mentioned, if you are detonating with 95 your engine have a problem, switching to 98 is just a band-aid, you need to find why is your car detonating when using 95.

 

It's not the gas. Check your cat, don't just assume it's suddenly fine or switch back to 95 and see if the issue returns.

 

Its amazing how change of fuel can totally change engine characteristics, its a HUGE AMAZING improvement. Before it was like a slow donkey now its feels like max power. How can this be if cat was damaged?

I still think 98 octane(94 us) is the best fuel for the car and anyone filling lower will get damaged cat/coils/plugs, bad recommendation from Mazda. I have to add i also changed 02 sensor some time back because Mazda put 2011 sensor last time which would not communicate properly with the ECU. After changing to 04 version Denso DOX-1449, it worked perfectly.​​ I agree i still might have a damaged cat, but i suspect wrong 02 was the reason. Seems to be really important on this car!

With 2011 O2 sensor(Denso)

With 2004 Denso DOX-1449

 

Change back to 95 and see if the issues return. Gas octane just doesn't make that much difference, so by jumping to conclusions you're ignoring the real source of the problem.

Which O2 was it? If it's the front then yes that would cause all kinds of problems, it's really important on any car this side of 1992.

 

Yes it was front o2, can it be that many owners have wrong 02 sensors, like some oem garbage, making it one of main culprit for cat failures?

 

Unlikely? They rarely need to be replaced. By the way the readiness state your screenshots show takes time and drivecycles to be set after the battery is disconnected. It doesn't actually show a failure like the sensor is malfunctioning, it's showing that it hasn't completed the checks yet.

 

No in this instant i drove several hundred miles with the 2011 sensor and it would never complete, after i put 2004 sensor it took 15 minute drive, i do have 2004 car. The reason i changed it is because i suspected it was wrong model, i knew Mazda messed up like usual. I will change cat either way and stay on 98 fuel forever, the car loves it.