I have an 88 S15, with the 4.3. It was my daily driver for many years but has been relegated to "sometimes used" category now. It probably leaves the yard only a half dozen times in year. Doesn't really justify still having it but here we are.

It has developed a problem lately (like yesterday, actually) where it won't start when hot. It had done something similar once or twice over the last couple years, but if I open the throttle half way or more, then crank it over a few turns it would usually finally start. Runs good, no other motor related issues that I'm aware of. Has 177,xxx on it now. Uses a little oil, leaks a little here and there, so I don't really know which is the main culprit, but who cares?

I drove it about twenty or so miles yesterday, shut it off for five minutes or so and it started up with no problem. Drove it another mile or so and let it sit for twenty or so minutes. Came back and it fired maybe twice then nothing. Just cranks and cranks with not a pop. Seems it getting plenty of fuel from the injectors when cranking. Has spark all the way to the plugs. It just will not fire. I tried for nearly an hour, waiting five or ten minutes at a time and cranked on it till I ran out of battery with no luck. Had to get a ride home. Brought the battery home, charged it up and went back today. It started right up like always. Ran fine all the way home. I pull it in the yard ans shut it off. Tried to start it and again, two or so hits and then nothing. I believe once it cools down enough it will start again.

So what's going on here? If it's not lacking for spark, then it must be be somehow fuel related? Maybe a temp sensor giving false readings? Maybe over fueling and flooding?

 

My 91 was being selective about starting, I thought it was a hot/cold issue but turned out to be a combination of bad ignition switch and fouled plugs.
Your issue might be a few things.