Any ideas why both of my cats failed?
 

2018 BRZ, MT, ~36k miles, JDL UEL catted header, OFT stage 2 tune, 93 octane gas, K&N drop-in filter

So a few weeks ago my car started exhibiting a huge loss of power, and also had an odd drone in the exhaust note. It felt like anything over ~20% throttle was ineffective. On the highway I'd lose speed when going uphill, and couldn't regain it until going back downhill. No CELs. I cleaned the MAF sensor and PCV valve, and also found that the clamp connecting the intake tube to the air box just after the MAF was loose and tightened it. I measured the resistance between the various wires on the two O2 sensors, and found 2.5 ohms between the two black wires on the upstream sensor, and 5.8 ohms between the two black wires on the downstream sensor, and no connection between any other combination. No changes in power yet.

I also took a look at a spark plug (photos attached). I chose plug #3 because several months ago I had a #3 misfire CEL pop up out of the blue while on the highway, but after clearing it everything seemed fine. The tip looks a little black, but it didn't wipe off on my finger like if it were soot. I went ahead and got some replacement plugs but haven't installed them yet.

Next I found an exhaust leak at the header, and ordered all new gaskets. When I installed them I took a look inside the header, and found that it was now catless. So I also removed the front pipe, and saw that it too was now catless. The remnants of both cats were crammed inside the front pipe where the diameter gets smaller, mostly blocking the exhaust. Removing all of that (and loading the stage 2+ tune) fixed the power issue, but now my big concern is finding and fixing the original issue before replacing at least the second cat. From what I've read, it sounds like an excessively rich fuel mix or unburnt fuel reaching the cats is what would cause them to fail, but I'm still not clear on why or if that's my case.

Here's a log from back when the exhaust was clogged:
https://datazap.me/u/kambroso/log-16...0?log=0&data=1
And here's a log from the other day:
https://datazap.me/u/kambroso/log-16...7?log=0&data=1

Any ideas of what could have caused my cats to fail, and whether I still have that issue? Let me know if I didn't log the proper items to diagnose this issue. If that spark plug does look bad to you guys then I'll go ahead and get those changed out, and let me know what else I should check. Thanks in advance!

The cats in JDL products are low quality, I had mine rattling in the front pipe after one track weekend...

I have a AFE catted header and the cat went bad after throwing a rocker arm. I had to drive 30 miles to get home. I was told running rich will kill a cat. I knocked it out. I replaced the secondary cat with a Nameless 2.5" catted front pipe with a Helmholtz resonator. Been living happily ever after.

JDL cats are known for being low quality and dissolving. Combine with a stage 2 tune that is designed for catless headers, and you probably killed them.

log doesn t tell us much about your fueling since it s all closed loop
the trims in those anyway is acceptable
You should log a full throttle pull to redline and maybe modify the tune to suit your car better if it that will be the case

The OFT Stage 2 hardware requirements call for a catted header, but you're saying it's still bad for that cat? I've also run the E85 tune during track seasons, which says catted or catless header, perhaps that tune isn't great for the cat either?

I'll post a new log as soon as I can.

Intake leaks and exhaust leaks cause the sensors to read inncorrect data and make fuel adjustments incorrectly. You were likely running pig rich due to the leaks that killed the cats, plus E85, plus lower quality cats, plus a shelf tune....values were probably all over the place.

Nobody asked.
Pop tune?

I'm not sure what that means. A tune that makes popping sounds in the exhaust? Does that work by letting unburnt gas into the exhaust? If so I image that would ruin the cats quickly. The tunes I use are the regular ones downloaded directly from the OFT site.

So I broke it? That sounds about right.
Well the leaks are fixed, and tomm.brz has offered to help customize my tune, so hopefully I'll be in better shape soon.

Yes they are a horrid tune that some use to sound "cool". They will blow cats away. You would have know if you had them!

Don't worry, worst case scenario is: de-cat the header or maybe work with Jesse at JDL for a replacement if you are the original owner.

Here's a 2000 rpm to redline WOT pull in 3rd:
https://datazap.me/u/kambroso/log-16...zoom=2990-3140

tune is much improveable
but i don t think it killed the catalyzer, i think was because of unluck/bad quality