Hey not sure if this is the right place to put it, I recently got a p0421 CEL and ended up doing the 01+ manifold swap with racing beat extensions and welded bunge. However, it still throws the code, even after clearing it. Did I miss something?

 

yes. the fact that it could be the sensor and not the cat

 

You need to move one of the O2 sensors downstream past the cat, IIRC.

 

Hey guys,

Thanks for the reply. The o2 sesnor is a new bosch sensor. I did move the downstream o2 behind the cat. I'm afriad that its the actual cat itself. After replacing the pre-cat I cant believe i still have to deal with this issue.

 

What year is the car and do you have emissions testing where you are?

Personally I'd just buy a testpipe or bust the insides out of the cat you have and run the antifouler but there's no emissions in FL to deal with.

http://www.summitracing.com/parts/rn...3OehoCNf7w_wcB

 

The car is a 2000, the pre-cat was toasted when we pulled it out. did the 01+ header swap and rerouted the o2 sensors.. still throws the code.... probably the most frustrating thing ever. I live in california

 

The precat usually goes to crap when the coil packs are failing on NB1s. Might want to try replacing those first, or upgrade to the Fab9 COPs. Otherwise you're just crapping up another good cat. It doesn't take much.