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

 

sometimes the code hints at something upstream or downstream being the culprit and not actually the obvious.

cat codes can be thrown because of o2 sensors or a bad cat but you have to think about what causes the cat to fail in the first place.... running too rich or burning oil.

the cat can also deteriorate from running too rich and having hotter exhaust temps at the cat for long periods of time. if you added a cold air intake, header and better flowing exhaust you could be running super lean and it would only take a few weeks/months to kill the cat and o2's from running lean. i've had seen a few that the metal cage melted and all that was left is the ceramic left.

if you are running anything other than a bone stock swap you need to put money towards getting a chipped p28 and getting it tuned. running rich/lean for too long can do all kinds of bad stuff from killing your ringlands to cracking a sleave.

 

Thanks for the reply. The whole point of taking off the check engine light is to pass the emissions test which is up at the end of this month. Will that effect the test since i will be using a jumper from obd2b to odb1? Can i use a P2P ecu chipped and do you think that will pass? Thank you

 

What state are you in? If you have a half competent smog inspector/tester...that jumper harness for an OBD1 will not work and neither will a chipped P2P.