We just got my 16yo this truck. We got it from a friend who told us everything about it with no mention of this problem, and it did not happen to him previously. We are friends with the seller and I believe he is being honest because of all the information he gave us.
It started fine the day we picked it up. It had a slight irregular miss. Idle speed was high, around 13-1500 rpm. It cruised at 35 mph on a flat road with out any throttle input. When we got home, I pulled the cap and the cap and rotor contact were black. There is a decent exhaust leak, manifold to ypipe. We got it for a song and figured we can take care of these things.
The truck sat on a slight incline for 2 days. We were going to clean the cap and rotor and figure out the engine miss and exhaust leak. It turned over and fired for a few seconds, then died. Tried again with some throttle and it did the same thing. Then it just cranked and did not fire.
We towed it to the garage, charged the battery and tried again. The check engine light comes on with key on. We can hear the fuel pump turn on and run continuously. I checked for spark and we are getting spark at the coil wire and at the cylinder. Checked the fuel pressure regulator by pulling the vacuum line, dry. Checked the air filter, its clean. Ohmed the idle air control, 10 ohms, the manual says thats good. We tried it several more times. It fired once and ran for a few seconds.
The next day, it started ran for 15 seconds, then quit and would not restart. Checked fuel pressure, 5 psi initial, 45 psi with key on. Plugged a noid light in and it flashes while cranking. Connected the code reader, it could not communicate. Verified we still had spark and there is. We had to leave for a few hours.
Tried it one more time just for giggles. The pump ran for 1-2 seconds and shut off. The engine started for 5-10 seconds and died. I cycled the key, fuel pump 1-2 seconds, engine fired and died. I tried again, fuel pump turned on and did not turn off. The engine just cranks with no start. I forgot to check fuel pressure after this, but it was 45 psi with the last crank attempt and it holds that pressure for a long time, an hour at least.
Any help would be appreciated.
Thanks

 

Key terms in your post:

We can hear the fuel pump turn on and run continuously
Connected the code reader, it could not communicate

You have a failed computer (PCM). This is a very common issue with these older trucks. The cause is the capacitor(s) are leaking inside the computer. Dozens of recent threads on this forum for this very issue. Plenty of pics and basic instructions to remove the PCM (from inside the cab on your truck) and how to replace the capacitor(s) yourself if you are handy.

I use the term capacitor(s) because early model trucks have only one. Yours may have one or three.

Welcome to FTE!