2006 nissan pathfinder. what would cause smoking bad and burning oil?

What is your question?

2006 nissan pathfinder mass air sensor went out which caused plugs to foul and catalytic converter to melt. i changed sensor plugs and knocked out the converters and now it is burning oil and smoking really bad. it did not smoke before or after sensor went out and suggestions? the pathfinder has 250,000 miles and i checked pcv valve and it is ok.

What makes this problem better or worse?

same all the time

How long has your 2006 Nissan Pathfinder had this problem?

now