I need a new cat for my f350 and I can't find one for a ca state legal how can u tel witch o2 sensors are bad?

 

I'm not sure in CA but in NV if you have a heavy duty truck (8800+) you have higher limits for emissions and are not held to the same standards as light duty trucks . They only do a visual to see that a cat is present, so, I would say that you could use one that fits and call it a day. DISCLAIMER: this is what I did to mine. Passed inspection and emissions.

O2 sensor: is your CEL on? If not I wouldn't worry about it.

J