Alright so this story is about my friends mo (I am a Honda man for life, sorry Nissan boys) but the thing's a dud so far and its his first car so we eager to fix the problem. Had some misfiring issues, etc etc all taken care of as far as we know, but apparently something was wrong with his cat and it is causing really bad gas mileage? I know this post is pretty vague but we haven't been able to figure out what it is. New spark plugs so that rules out those. Anyone with any experience that could help a brother out?