1991 s-10 blazer won't start, no spark at distributor

I don't think 3 months makes stale gas, maybe year old gas, but not your short time. And if not mistaken, I think you have throttle body injection on an '89 chevy, although chevy always was a little behind the curve on new improvements to cars. hint, hint.
The computer has everything to do with it. it controls ignition timing, it controls spark, it controls the fuel pump and the injectors. Since it won't start with starter fluid or gas, next step is to look into the ignition system. Check for spark on a couple of spark plug wires. If you have a blue, snapping spark, you can assume your ignition system is working well enough to start the engine. Take a spare spark plug or pull one of your plugs from engine, attach the plug wire onto it, and lay the plug on a metal piece of the top of engine-the spark plug hex and threads is the natural ground for the plug, so if you lay the threads on a metal piece, or hold it tight against a steel bolt, you can observe the spark jumping the gap, and no danger of getting shocked. But if you hold it, just in case, wear a glove or wrap a heavy cloth or rag around the wire. Remember, a blue energetic spark has to be seen to verify good ignition. Oh yes, you need a helper to crank the engine over while you watch for spark. If no spark, and you have a distributor, check the coil wires output at the end that connects to center top of distributor.Pull it from distributor and hold the metal end terminal no more than 1/4 inch from a ground source, a bolt or the frame, or an engine bracket. Helper has to crank the engine over, and watch for good blue spark. If no spark there-ignition: coil, crank position sensor (or maybe a pickup coil inside your distributor-same function), ignition control module, computer, and all the associated wiring.
If coil has spark, but none at plug wire ends, inspect closely the distributor cap and rotor. not passing current or shorting out there.
So the basics are, to run, the engine needs gas, air, compression, and a timely spark.

Could be your distributor cap/rotor and maybe spark plug wires. Does the engine turn over at all?

Pull off one injector connector and use a test light or voltmeter to see if one wire has power with key on.
Power to the injectors is fed through the ignition switch, so with key on, you should have power there. The injector ground is inside the ECM. If you have power, you'll have to diagnose the circuit for why computer doesn't ground the circuit when it should.

what happened the last time it ran

did it run hot or ??

Check the oil - if none -- you could have turned a bearing. In that case, the next would be a compression test.

Best regards
Ck

Whenever I had this problem, it was always cured with a new set of GOOD spark plug wires. Not generic set off the parts store shelf. Get some moisture removal spray and put it on both ends, the coil and the plug, before putting the wires on. Do one wire at a time so you do not get them mixed up. I do not think you have a distributor or a cap. If you do replace it also as it is over 20 years old.

if no crank sensor by timing cover, some vehicles are controlled at the distributor. the 95-96 have sensor by cover . before 1995 this its controlled by distributor. there is no "crank sensor" on that engine the pick-up coil inside the distributor acts as the crank reference for that engine. have a good day !! 4.3 vortex engine.

Sounds like it could a bad coil.But if you wait until it does start take a spray bottle of water and while running spray the distributor cap and listen for it to start missing if does replace the distributor cap if it does'nt replace coil.

check the ignition coil also, check to see if it is sparking against anything metal

most of the time the module will fix it. it's cheap and easy to replace.
just remove the distributor cap and the rotor and you will see it.
however, according to your info, the blazer does not have a vin code W in 1985. that's a 7.4 liters engine, the full size blazer only have 5.7 liters

factory immobiliser cut in by the sound of it