I love the 4.3L I have a tricked out 2000 S10 with that motor and its awesome(a few aftermarket bolt ons and those motors really scream!), I have also had an 89 Jimmy and 96 S10 with that motor so your in luck as I I know it inside and out.
The fuel pump is always a pain on trucks becasue you have to remove the tank to gain access. The pump is bolted in on the top side of the tank. I hope it doesn't have a full tank of gas as it needs to be drained(re-use when job is complete). Not to mention pulling a tank that's full of gas very heavy.
See this link for an overview:
Here's how you test the fuel pump relay, and fuel pump:
- Turn the ignition OFF.
- Remove the relay.
- Locate the two terminals on the relay, which are connected to the coil windings. Check the relay coil for continuity. Connect the common meter lead to terminal 85 and positive meter lead to terminal 86. There should be continuity. If not, replace the relay.
- Turn the ignition key OFF for ten seconds.
- Turn the ignition key to the ON position but do not start the engine.
- You should here the fuel pump operate for two seconds (a light electrical humming sound).
- Apply a 12 volt fused jumper wire to the fuel pump prime (test) connector. This should be located in the driver's side of the engine compartment. The fuel pump should operate.
- If the fuel pump does operate, remove and test the relay. If the relay is defective, replace the relay and repeat the test.
- If the relay is operating properly, connect a grounded test light to the fuel pump relay control wire (green with white stripe) at the relay. Turn the ignition switch to the ON position. The test light should illuminate for two seconds and go out. If the test light does not illuminate, check the relay control wire for continuity and repair as necessary, then repeat the test.
- Connect a grounded test light to the feed wire (orange) at the relay and turn the ignition key ON. The test light should illuminate. If the light does not illuminate, test feed wire for continuity and the fuse in the underhood fuse relay center. Repair as necessary and repeat the test.
- If the fuel pump is still not functioning, connect a fused jumper wire between the feed (orange) wire and the fuel pump motor (gray) wire at the relay. The pump should operate.
- If the pump does not operate, check the fuel pump motor wire for continuity and repair as necessary.
- If the pump will still not operate, replace the pump.
- If the pump does operate, start the vehicle and remove the relay. The vehicle should continue to run. If the vehicle stalls, check the fuel pump/oil pressure switch and its wiring. Repair as necessary and repeat the test.
Also see figure 4 which is digram 3 from this link, this is the schematic on the fuel pump, the fuel pump's hot wire is tan with a white stripe, if you can test the voltage of this wire you can confirm it is not an electrical problem.
Also be sure to releive the fuel pressure before servicing
- Disconnect the negative battery cable.
- Loosen the fuel filler cap to relieve fuel tank pressure.
- Connect fuel pressure gauge J-34730-1A or its equivalent to the pressure connection. Wrap a shop towel around the fitting while connecting the gauge to prevent spillage.
- Install the bleed hose into an approved container and open the valve to bleed the system. The system is now safe for servicing.
- Drain any fuel remaining in the gauge into an approved container.
Let me know if any of this is jibberish to you and I can clarify further.
Good Luck again, and feel free to ask anymore questions.