If too much fuel is the issue, it can be one of three things, high fuel pressure, a bad coolant temp sensor, or faulty fuel injector.
Here is what I suggest. First, check fuel pressure to confirm it is high (beyond the manufacturer's specs). Here are the manufacturer's specs. Also, if you look at pic 1, I highlighted the test port for checking pressure.
1993 GMC Truck S15/T15 2WD P/U V6-262 4.3L VIN W CPI
Fuel Pressure Specifications
Vehicle Powertrain Management Fuel Delivery and Air Induction Fuel Pump Fuel Pressure Specifications Pressure, Vacuum and Temperature Fuel Pressure Specifications
FUEL PRESSURE SPECIFICATIONS
1. Ignition "OFF" for 10 Seconds.
2. With ignition "ON, " engine "OFF" and fuel pump running, pressure should be 380-420 kPa (55-61 psi).
For additional fuel pressure testing procedures, See: A L L Diagnostic Trouble Codes ( DTC ) > Related Tests, Information and Procedures > A - E Charts & Related Test Procedures
If that checks good, then I need you to pay attention to fuel pressure drop off. Basically, you are checking to see how quickly fuel pressure drops when you turn the key off. It should maintain for a short period. It will drop off, but shouldn't go to 0.
Next is an engine coolant temp sensor. It is located on the front top of the engine. See pic 2. Now since this is an OBD1 system, you can check for diagnostic trouble codes, but chances are this problem won't show up. What can happen is the sensor indicates extremely cold temps. As a result, the computer makes the air / fuel mixture extremely rich to run the engine. Although the sensor sends an inaccurate reading, the computer doesn't know it's wrong, so a code may not show up.
With that, start with confirming the fuel pressure and let me know what you find.
I will watch for your reply. Note that most parts stores will lend / rent a fuel pressure gauge to you.
Images (Click to enlarge)
Friday, January 10th, 2020 AT 7:37 PM