if i put a new O2 sensor in my car, pre-cat, and the Cat was bad, what would happen?

 

I would assume that your car was an OBD2 judging from your sig then you would have a PO420 if im not mistaken which is a "cat efficiency low" code and a check engine light if it was failing. I believe that is a two trip code.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sickofitall1113 &raquo;</TD></TR><TR><TD CLASS="quote">if i put a new O2 sensor in my car, pre-cat, and the Cat was bad, what would happen?</TD></TR></TABLE>

well if its the primary o2 sensor (precat as you stated) then it wouldn't have any relevance to the "bad" cat because the primary o2 sensor reads the amount of oxygen in your exhaust and will richen or lean out the fuel.

if you are obd 2 then the secondary o2 sensor will throw a CEL since it reads if the cat is "bad".

 

well my gas milage sucks too. i did, however, just put back in my power steering and have been using the AC a lot. but its cutting like 45 or 50 miles off each tank.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sickofitall1113 &raquo;</TD></TR><TR><TD CLASS="quote"> have been using the AC a lot. but its cutting like 45 or 50 miles off each tank.</TD></TR></TABLE>

Yup, a/c will do that. Especially if your using it all the time

 

If the cat is bad enough to obstruct exhaust flow, then mileage could be drastically affected, especially if the brick inside has started to dislodge, break, or crumble.