EJ22 Catalytic converter(s) and O2 sensors?

[bodhicheetah]

Any info specific to the EJ22 catalytic converters and O2 sensors from those with experience and/or knowledge... much appreciated...

I have a '97 OBS, EJ22EZ, apx 340,000 miles on it. Had a blown HG and recently re-sealed just about the entire engine (HGs, valve covers/stems, rear main seal, oil separator seal, oil pan seal, oil pump seal, yada yada yada). And of course the intake and exhaust manifold gaskets.

Had the P0420 code before I re-sealed the engine but didn't really care. Now that I did all that work, I want it gone

I know I could have done a bunch of testing... but.... I was just going to start with replacing the front sensor to see if that was the problem. However, the old one is seized good and proper. Now that I have to drop the front Cat to try and get the old O2 sensor off (A/F sensor? people seem to call it both...), I'm going to order a new Cat to have on hand in case the old Cat is indeed bad. 

Questions are:

• Aftermarket part number for the front Cat? Or both front and rear for that matter? OEM is discontinued.  This one from Eastern Catalytic seems like the right one for the front, but I guess I'd have to plug the downstream sensor hole as the OEM one doesn't have that hole.
   
• Should I bother replacing the rear Cat? How often do they go bad? Or even if they do, if the front one is working, does it matter?
   
• Are the upstream and downstream sensors the same for this model year? They look the same, but I can't find a definitive answer on that. I'll probably replace the rear sensor just to be safe. I went with a Bosch 13445 (supposed to be same as Subaru 22690AA220) which I'm pretty sure is the right one for the front, but I'm not sure about the rear. I know for most cars, the upstream and downstream sensors are different, but they appear to be the same on this car.
   

Anyway....I searched around but couldn't find a good write up or whatever specifically about EJ22 Cat/O2 sensor problems/fixes/part numbers... so I thought I'd ask here. 

Thanks in advance! 

Edited February 2, 2019 by bodhicheetah

[GeneralDisorder]

Buy a header and catless J pipe. Install a 90 degree O2 spacer between the pipe and the secondary O2. That will handle the code. 

Aftermarket cats are not going to work. They never do. Either delete the cats and use a cheater, or put on OEM cats from Subaru. Nothing less is worth doing. 

GD

[ronemus]

The rear O2 sensor is more likely to be the problem.  If the front is bad you would have poor fuel mileage/soot/power loss as well as the P0420.  I agree that the aftermarket cats aren't worth it - federal regulations only require them to have half the life of OEM; stick with Subaru.  It's good to have the cat on hand - the O2 sensors are difficult to get out and it's easy to tear off the bung; use a backing wrench to improve the odds.  IIRC the bungs don't have flats, so you'll need a monkey wrench or very big vise grips.

[bodhicheetah]

Thanks for the replies! Gonna think on it for a bit I guess, see if I can find a compatible OEM Cat. I could straight pipe it if need be because I live in an emissions exempt area currently, but when I move I’d have to pass inspection. 

Why’d they discontinue the OEM Cats? Are there other/newer Subaru Cats that are compatible for my car? 

[lmdew]

Have several Subaru Cats up in the Garage, from cars that were scrapped.  If you pick it up in Colorado Springs $25

[bodhicheetah]

Thanks for the offer! It's a 6 hour round trip for me, but I may very well do that. I'll PM you if that's what I decide.