I just installed my stainless works long tubes and high flow Y-pipe and have been throwing p0430 and p0420 codes. catalyst efficiency below threshold. also getting random misfires under hard acceleration. then pulled a code for misfire in #1 cylinder. I replaced all the wires and replaced the #1 plug thinking I may have damaged it during the header install. the plug looked good. took it for a drive and still pulling misfire code. any ideas?

 

Dumb question but didn't see a tuner in your sig.
So. Did you tune it?

 

it is tuned but not after the headers. Is it necessary to tune after the exhaust change??

 

YUP ITS NECESSARY

 

Thanks, I didn't realize it was such a big deal. I don't really consider headers a major mod, but I am used to my old school 68 nova.

 

Also, if you threw that code your rear O2's are still active, have your tuner shut them off, they only give cat efficiency, so they are needed if there are no cats.

Dustin

 

Adding headers increases your air flow. So the PCM is tuned for alot less flow than whats actually occuring. With your F/I that's not good by any means.
Now that you dont' have cats the 02's think they aren't working so they need to be shut off.
As for the miss, I'd imagine it's because of the AFR being off while running F/I. But that part is a guess. Mine never did miss, but I also don't have F/I.

 

I'd check your wires to see if there's enough clearance from the headers. Just the right amount of heat will melt the wires, and there's another code to deal with. I have the Pacesetters and I bought jackets for the wires, ran me about $30 for the set of 8. PM me and I will send you the link. Preventative is always good.

 

my wires are all fine and I am still running cats. I am running the stainless works y-pipe with high flow cats.

 

Good deal... sounds like you've got it taken care of...