hi all, i have a 02 accord lx AT that had an A1 engine in it before it took a turn for the worse, i was constantly getting misfire codes, flashing CEL (p0420) turns out i was running on 3 cylinders, decided to swap out the engine at the time the only engine i found was an A4, had some issues at first with the throttle but somehow my mechanic got it to work, drove the car home, about 30 miles and the CEL came on once again it was a P0420 code, so i started to do some research in which the consensus seems to be a bad Cat. converter, especially since the CEL was flashing meaning damage to the cat before the A4 engine was put in. Now 4 months later i have to pass smog in CA of all places; the local honda dealer wants to charge me $800-$1200 parts and labor for the new cat. my question now is can i buy the cat that my local parts store has (CA. compliant) around $270 they dont specify if it will work with the ulev engine, i know the A4 engine has a diff. oxygen sensor (wide band) which was left on when the swap was done, but now that i need a new cat should i get one for A1 engine or the A4 engine, or does it really matter? any help would be appreciated, Thanks Guys!!

 

misfires probably killed your original cat. I'd replace it with a magnaflow 46615 or 446615 and recycle the old one at ConverterGuys.com - Core Buyers - Scrap Catalytic Converter Recyclers - I got ~200 bucks back for mines. see this thread for more info:

99 Accord Code P0420 - Cat.Conv? Need help - Honda-Tech