One way I check the output of the coil, is to take a known GOOD plug, and ground it against the frame. Do you have a yellow spark or a blue spark? Yellow is weak, Blue is strong.

You can also disconnect the coil wire from the dizzy, use a long screwdriver or one that will fit in the end of the coil wire and ground it against the frame. Same thing goes for the colors. Even though it's stock from '93, it could still be good. I had a problem with a 2 month old MSD Blaster coil, and when I put the stock coil back on, the truck started immediately. The MSD coil wouldn't fire when cold, but would if I warmed it up with a hairdryer.

If in doubt about the operation or age of the O2 sensor, I would spend the $45-$53 for a new one. Just eliminate that problem all together. If you do a search under my name, you will find a wealth of info in regards to problems with either a RICH or LEAN situation.

Also, what plug gap are you running? If the stock coil is weak and you are running .56-.60, you could very well be runing rich. What plugs did you install or the mechanic install? Regular Motorcraft coppers' or Autolites? Anything other than those 2 will also give you problems, i.e., Platinums, Splitfires..

Hope this helps..