Cantu6.0

Ok i bought a 99 civic hatch and its always had the check engine light on. So i conected the scanner and this came up P0420 (http://www.obd-codes.com/p0420) so now i took off my whole exhaust andn disconnected the ecu. The cat did take **** so i figured that was the issue. I installed the 2 1/4" pipe and installed DC headers with a Aftermarket CAT. The P0420 still can on. the p0420 still came out. i did the mini swap on it but did not wire vtec just yet. My bro did a engine swap on his honda 96 hatch (which was not throwing no codes perfectly fine) i installed his header/cat with 02's to the 2 1/4" pipe (headers had the common crack down the middle.i welded it with a cast iron rod (im a combo pipe welder) i preheated it and welded shut which by the way it was a hair crack. now i plug up the ecu back up and drove it around and the check engine light turns back on. . I checked it with the scanner and it now gives me the P0420 & P0430(http://www.obd-codes.com/p0430). Im running out of ideas on how to fix this issue without throwing allot of money away(new 02s and cat). The car also idles low and rough when i come to a stop not always but often that you'll notice Has anyone ever had a issue like this please help

Perfectionist

Interesting reading...
http://www.professionalfleet.com/lan...nverter_repair