two problems, possibly related?

[GSEclipse06]

ok my car has two issues. the first problem is that it blows alot of carbon. i had a new exhaust put on recently and within a week the entire muffler tip was covered in black dust.. i thoguht maybe it was running too rich/lean (im not sure which one creates carbon). well last night i was with my friends adn one did a random oil check on his car, and knowing mine is about due for one, i decided to check mine too. good thing i did, becuase i had almost NO OIL whatsoever. i remembered seeing an extra quart in the trunk when i bought the car (this is probably why) and i put it in, ran it for about 30 sec at idle to let it circulate through, adn checked it again...almost no change. the pep boys was closed (what the hell kind of place like that closes at 8 pm on saturday) so i went to a bp and bought a quart....now its a bit over full. my questions are: what could be causing the carbon issue and how cna i fix it? does anyone know of major oil loss issues with the 1.8 liter SOHC motors that could help me pinpoint where the leak may be? could the two issues be realted? thanks.

 

[Hughes]

When you replaced your exhaust did you replace the o2? You might want to check it.

 

[GSEclipse06]

only the rear muffler section was replaced, and it was blowing carbon before that (i had a badly-rigged fart can on the car which was why it needed replaced, it had carbon all over it too but i thoguht it was from the car before mine)