So, about two weeks ago I had a custom 2.25 inch exhaust put in to support my turbo set-up with a Magnaflow performance catalytic converter. Everything has been fine for the last three weeks since it was installed.

I had the car tuned on the dyno last weekend with no issues and now, over a week later, I have a CEL for code P0420 "Catalyst Effeciency Below Threshold". The interesting thing about this is that the car has been perfectly fine for the last three weeks with no CEL's and now it just randomly pulls one 300 miles after the cat has been installed and after 4 hours on the dyno.

I'm in the mood to point fingers at my car, but I am having trouble pointing it at the O2 Sensors (my wideband works perfectly fine), the brand new catalytic converter, or the exhaust piping.

Anyone want to share Ideas?

 

just put some sort of anti-fouler on the o2 sensor and clear the code.

 

yeah, run a anti fouler style set up on the rear O2.. they DO work

your probably just outside of the correct range, which means the PCM is taking a bit to call it out of whack,
an anti fouler will fix this.

 

thanks guys, I will look into getting one of these.

 

Is that the same as the Greddy O2 adapter? If so, which sensor does it go on? I know on the xB there are two O2 sensors on the exhaust piping.

 

it would go on the second o2 sensor after the catalytic convertor.

the first o2 sensor should be before the cat to get a reading of the exhaust before the cat cleans it up, and the second o2 sensor verifies that it doing its job. so that is the one you need to trick into thinking the OEM cat is there and functioning properly.