background: a couple years ago when i first got the car, the tach needle would fluctuate a LOT (jump to 8000 RPM and then to 3000 RPM then back up to 5K, then 0, but it didn't reflect the actual engine speed). my dad was driving the car at the time and he had to keep downshifting to keep the engine alive so we could make it to the nearest auto shop. after a few downshifts, we hear a loud backfire out the muffler, but fortunately there was a shop right down the corner.

fast forward to today: i've had a CEL code 67 for a long time now. in my pretty much stock 97 integra, i'm failing smog with a 500+ HC reading and i need to get a smog check by next month. i get ahold of a new stock cat (thanks LOwrestling2001). i finally get myself to install it today w/ a friend and my trusty torch. previous attempts failed b/c the nuts were rusted shut on there. i had to remove the whole b-pipe/cat from the header to the axle-back.

looking inside the old cat, i see the ceramic honeycomb material is all but gone from the second half of the cat down. my secondary o2 sensor also looks pretty messed up too. the outer metal casing (with the holes in it) is half gone.

anyway, with the new stock cat on there, the car feels like it runs better. really. the idle has improved a lot.. the needle doesn't fluctuate too bad at idle anymore and it stays at a constant 750-800 RPM. the car also feels more powerful, and i usually don't notice these things (i couldn't tell a difference with the AEM CAI on). it could just be the cold weather this evening though.

just wanted to share my experience

btw, will i have any problems at smog time with the damaged secondary o2 sensor? that little probe that sits inside the metal casing is exposed. it's not as important as the primary one, am i correct? if i recall, the secondary one is just to tell the ECU if the cat is doing its job, right?