I have a 1997 Sierra with the 4.3L V6. Recently I had a problem with it not starting,
http://www.automotiveforums.com/vbul...d.php?t=664144, which I think is probably related to the cap/rotor. After that I got a MIL and it gave me an O2 sensor code. After a couple of days the MIL went off.
The light has since come back on and remained on. I am now getting really bad gas mileage. I haven't had a chance to get it in to have the code read, but I'm suspecting the O2 sensor again.
Would a bad O2 sensor cause poor mileage? Other than the mileage, the truck seems to be running fine. It does smell a little rich, but I'd expect that with the mileage I'm currently getting.