Getting a PO420, System Efficiency Below threshold..????? What the hell and still runs like a charm too...

 

What that code is attempting to tell you is, the polluted exhaust is coming out without being cleaned up.
It may be running good now , but because it is extra rich , there is a reason and if not corrected soon enough it can and will destroy the converter. They are very expensive to replace and if not corrected will destroy the replacement converter. Suggest you look into that ASAP.

 

Thank you Hanky, I will check it out pronto.. will keep yas posted on the problem.