I feel sorry for convertibles, motocyclists, bicyclist, EV drivers stuck behind a decatted rotary. The irony with the latter category is especially hilarious.

 

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, 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!

 

Have you actually had a look inside the cat? It can be causing damage without glowing.

 

Continuing this discussion. I started data logging obd2 cat temps and am seeing temps as high as 1730f just driving around. I understand this may not be the actual temp of the cat as the ecu uses multiple sensors to “calculate” the temp data.

Can this data point be used to determine cat function or condition? From what I can tell the functional max range seems to be around 1600-1800f. Interestingly I noticed reports of even catless pipes registering similar temps.

So does this data tell us anything usable?

 

Took my midpipe with working cat off a few years ago just after purchase. Lives on shelf in shed just in case its needed.
Every time i drive the car i see EGT temps via OBD up to 1750 (950C plus for me), this was the same for both the old tired engine and fresh engine.
This car does not see any tracfic at the 100km speed limit that i always do! 😉
Can't help you with data of those temps being detrimental to cats as i only drove a few times with cat installed. Im more of a dog person! Very likely though.

 

If your cat were to clog you might see higher temps than that. By itself the temperature doesn't say much, although I did find it interesting that the temperature climbs when you're in low regimes and decreases when you open up. At least that looked like the pattern. Possible it was shedding heat better with speed.

 

Interesting that you mentioned that. I noticed the cat temps can be maxed out by driving at medium/low load on the highway. 80mph in 6 gear about a 1/4 throttle. Max temps will be around 1750. If I got WOT, the temps actually drop to about 1680 and stay there until I let off.

I guess at least I know the current functional range of temps under light duty driving. I know if temps spike from there on track to shut it down.

 

Exhaust temperatures are highest near the stoichiometric mixture ratio. At high load, the ECU will switch to open loop enrichment (you will see that in the AFR from the wideband O2), which cools the exhaust. It is commonly noted that the stock tune is very rich near the max rpm - I think this is done to prolong the life of the cat.

 

The logic follows since temps seem to drop when going to WOT.