I don't know the '91 Explorer, if it has fuel injection then this may not help.
Find the fuel line into the carbuerator, should be a fuel filter very near that. Disconnect the line between the filter and caruerator (if the filter housing is built into the line, just disconnect from the carbuerator), get a spill can set up to the disconnected line, and have some one turn over the engine. You should have fuel shooting out of the line (be careful here not to let it shoot around the engine compartment).
IF it just trickles out, or not at all, your fuel pump is shot. If fuel shoots out of the line when you turn the engine over, you should try replacing the fuel filter. IF your getting a strong stream through the filter, new or old, you need to have your carbuerator looked at.
Source: from experience with other vehichles.