Rats nest and air pump question
 

Would like to reconstruct my exhaust, the PO installed resonator in place of the cat and had the tubes for air pump welded into it. I'm wondering if i just disable the air pump if that would have any effect on the rats nest or gas mileage?

Another question, i'm still thinking if i should keep the rats nest or not. Is there a way to test most of it's components to find out if there are still functioning? Also, is there a wright up somewhere that describes each individual component of the rats nest assembly?

Thank you very much for that, sir.