Rep Power: 0

Hello all i got my first honda civic recently. Always been a Chevy guy. I have had to do a lot of work to make it pizza delivery reliable. Its a 2002 civic HX model. Had an exhaust and headers on it when i purchased it and the upstream sensor was bad so i replaced that after doing the head gasket to make sure it wouldn't just mess up again as i had exhaust gas going into the radiator. Then i got the p420 code so i got one plug de fouler after finding that fix and the p420 code came up again also i notice a sputter before it throws the code. so I ordered a 90degree de fouler. I used that and the straight i drilled out then tried again. Still get a sputter and cel came back on and this time its a p1420. So I unplugged the downstream sensor as the car seems to run best that way but I have to look at that damn cel still. I would just remove the cel bulb at this point but guess that part of the cluster is led and cant. Any suggestions on how to sort this out would be great.

 
Rep Power: 511

Which O2 sensor are you putting the non-fouler on? If you put it on (what would be) the upstream sensor, it's not gonna clear that P0420 code and it'll mess with your AFR and thus, engine health. The downstream sensor is the one that looks for catalyst function and efficiency, and that's the one you're supposed to do the non-fouler trick on

as far as the P1420 code, I got nothing

edit: found this about P1420 troubleshooting over on honda-tech
Also this PDF: https://www.autocodes.com/uploads/honda/07-036.pdf. Sure, it has to do with the HCH and Insight, but many steps should be applicable

 
Rep Power: 367

potentially the cat is reeeealy in bad condition and you really need to replace it. They can plug - try to crap with your a$$ plugged to see how you feel - that's how the engine feels

 
Rep Power: 511

Cat delete @sdaidoji . HX uses the -A1 exhaust mani. OP got the car with an exhaust and header installed by previous owner

 
Rep Power: 0

It was the downstream after where a cat would be that i used the de foulers. Like i said what is odd is that when that sensor is connected i also get a sputter before the light gets triggered. if i have it unplugged car runs smooth as can be never sputters just runs perfect.but just have to look at that damn cel

 
Rep Power: 367

woups, looks like i can't read... sorry

 
Rep Power: 0

Yea. No worries. Well anyway from my past experience the downstream would only be there to warn if you have a bad cat condition and not effect car driving conditions. But i seem to be getting some mixed info reading here and there that on the hx model this sensor also communicates to the pcm to keep the lean rich condition right almost like the upstream sensor does. The fact i get strange sputters at cruising speed when its connected seems to prove this to me aswell. So if i had a P420 cause sensor 2 was detecting a rich condition then when i do the de fouler trick and then i get a P1420 could this just mean now im to far out of the stream and not detecting enough NOx? So if sensor 2 detects a lean condition it will cause it to run richer and if sensor 2 is detecting a rich condition the p420 it will make car run leaner. The hx model is a Lean burn it was called by the way.