Hey all,
Shortly after I bought my 350z, it started throwing P0420 error codes at high speeds "Catalyst System Efficiency Below Threshold (Bank 1)." Original cats with 80,000miles, so used it as an excuse to switch them out with Berk HFCs. That didn't fix the problem. So I swapped in a new o2 sensor onto the passenger side. That hasn't fixed it either.
Any other suggestions or thoughts what it could be? Bank 1 is the passenger side, correct?
Thanks everyone!

 

 

which sensor was it? each side has 2

 

Looks like I had it right. I switched Bank 1, Sensor 2. Since the code is relating to the efficiency of the converter, it wouldn't make sense for Sensor 1 to be the cause of the code.

 

try getting some exhaust bungs

 

What do you mean? The Berk HFCs have bungs built into them. That is where i switched the original o2 sensor.

 

I had this code come up a few months ago cleared it and now it's back. Sounds a little choppy from the cats at idle. Going to be boosting my car in the next 2 1/2 months I have art pipes sitting around I got a deal on should I just install those in the meantime or will I need a tune asap to not run lean.
Mods are just motordyne tdx2 and k and n drop in filters.