1991 Chevy S-10 fuel issue

Check for voltage at the injector. With the key on (engine off) you should have 12 volts on one wire at the injector -- (or one wire at each injector if there are two injectors). The other wire is a ground that goes to the ECM (computer). The ECM fires the injector by applying a ground to the injector.
If there is no voltage, check for a blown fuse.

Now you must determine if the injector is receiving a ground signal from the ECU - This fires the injector. You should use a NOID light. This is a little device that plugs into the injector electrical connector. When you crank the engine the noid light will blink -- this indicates two things -1. There is voltage and 2. There is a ground from the ECU. If the noid light does not blink then there is a problem with the ground to the ECU -- or (worst case) a bad ECU.
You can do this test with a regular 12 volt test light - but you can damage the electrical connector or over load the circuit if you are not carefull -- I believe Autozone or places like that will loan you a noid light for this test.