Originally posted by jeddy
I recently had a P0420 (cat efficiency low, bank 1) on my 00 RS. I have a Stromung 2.25" cat-back, Borla headers, and 47K miles. The mechanic i went to (Honda and Subaru specialist) says he sees these types of codes alot in cars with high-flow exhausts and headers. A lack of heat shielding on the headers can supposedly also cause this, since the exhaust loses too much heat before getting to the cat.
I was told this will cause no harm, but the cats may not be working as well as they could.
This is a catch 22: I have a Borla/ Apexi N1, 48K miles. I have been throwing CEL's a lot lately. (don't know the code yet) I took off the header yesterday to put in STi motor mounts and ThermoTec Header wrap. The inside of the header has heavy carbon fouling. So...somehow the O2 sensor is seeing an erroneous lean condition and is over richening the mixture, which is fouling the plugs, O2 sensor, Cat.....everything.
My other thought is maybe the Borla has a high enough flow that it blows the gasses through the cat too fast to burn fully?
I'm sure the header wrap will help, but I wish I knew which wire on the O2 sensor was the sense lead so I can test it at closed loop.
Are the 00' RS O2 sensors 0-5 volt? Is STOICH 2.5 volts?
Any help is greatly appreciated!