I'd second the Cat, but it could be a couple other things.
First thing I would do is check your filters, air and fuel.
If that done, the conenctor should be in the engine comparment on the F3. Ford didn't start using OBDII till late 95, so it will be a goofy ford connector, like the EECIV or something. Unfortuneatly sometimes you don't get alot of good info out of those older computers.
If HR/Monaco isn't helping you, try a ford heavy truck garage, they might have abit more insight. Broadway Ford in Saint Louis, Mo does a lot of work on Ford heavy trucks, they might have a tech that knows.
If you do find the conenctor, most Advance Auto's or AutoZone's have a scanner that a counterman will come out and scan it for you, the service is free. Most likely the counterman will have to "Fool" the scanner by selecting a "Close" vehicle like an F350 with the same engine/Trans.
"It's always wrong, everywhere, for anyone, to believe anything beyond insufficient evidence" -- William Kingdon Clifford
John (N9MXX) & Derek (KC9KEM)