Well here goes..my long and arduous history with this POS.. replaced my rear o2 sensor cuz it died. Then my cat plugged up..replaced it with a magnaflow unit, 2.5" I believe. Ever since I've had a p0420 "catalyst efficiency below threshold" basically not performing up to par...Replaced front o2 with known working unit.. code still remains...I'm just wondering WTF is going on..I WANT THIS CODE GONE, just tired of it being there. Took off manifold, new manifold gasket/downpipe gasket...Can't hear any exhaust leaks...so what the hell?? Do I have to use an OEM cat for an S-series? I see many many people have used aftermarket cat's and have not had the same problem as I do.
Any input anyone??