1986 S15 2.8L will not start

I have a S15 here that will not start up. i have replaced wires plugs distributor, coil,etc and even swapped the ecm with a couple different ones i got at a junkyard but still no go. I can unhook the ecm and still the engine gets gas and spark yet it will not run??. I checked compression to make sure timing chain had not jumped and it seems to be ok,
Started doubting my brain cell capacity and got some one else to check it out and they had the same luck as i did.
This lil truck formerly had a security system on it which was removed before i bought it. When the truck quit running it was running ok - i just shut it off and when i got back into it a couple hours later it refused to start.
I am getting both spark and fuel so this has me completely bamboozled- it should run in my way of thinking but obviously somethings amiss.
I did have a Mass air flow sensor fault or map i cannot remember exactly how thats called but the other guy that looked at it changed that too and still not running. It sounds like someone played with the wiring before i got it as its been customized and lowered etc. Any ideas?? i dont want to give up on it as i just put new bell tech shocks and some nice new tires on it a week before this occurred .

Is the battery in good shape?
Does the rotor button point directly at #1 sparkplug wire terminal on the distributor cap when the timing mark lines up.....you may have to turn the motor over a 2nd turn to get it to line up.
You might try pouring an ounce of fuel down the throttle then crank it over. If it doesn't light off then the ignition system would be the next thing I'd look at....a weak coil can't push a spark under compression.

Is the battery in good shape?
Does the rotor button point directly at #1 sparkplug wire terminal on the distributor cap when the timing mark lines up.....you may have to turn the motor over a 2nd turn to get it to line up.
You might try pouring an ounce of fuel down the throttle then crank it over. If it doesn't light off then the ignition system would be the next thing I'd look at....a weak coil can't push a spark under compression.
I tried three different coils ( none of them new ones but out of three i figured at least one would be good and changed the distributor itself with another used one and put new cap rotor wires plugs etc in the engine . I poured a tad of gas into the throttle body as well. I checked the timing by making sure i had the right compression as if the valves were not opening at the proper time i didnt think my compression would be right.i began to doubt my "shade tree mechanic " methods so i took it to a fella who works on cars for a living and him and his buddy changed the ecm a couple times(used parts) and switched the Prom etc and thats when he seen it had spark and gas coming even with the ecm unplugged and that to me seems unusual but they could all do that ? I could pull the motor and change it fairly reasonably but if its a wiring problem in the truck itself that would be a pretty big job for nothing.
My friend checked something else i think its called a knock sensor - me i thought crank sensor but apparently it doesnt have one of them.
I do have yellowish blue spark and i wasnt sure if that was the right color but He thought it looked ok and i checked it at a front plug in each side.
The lil truck would be a good one for a small block cause body is already customized but with the stainless exhaust and stuff and with perhaps having to raise it back up that way and i just put the new belltech lowered shocks in it i want to get it going with same motor as it has without any further adjustment cause now i have a quite a bit of cash in it and i only drove it one month.
I did the TDC timing thing by using my compression tester and when the needles moves i turned the crank til the number one piston was at the top ( fine long screwdriver ) and wired the distributor that way to ensure #1 was at #1.
The battery is now Junk - it was working ok when i quit driving it and since then has started to fail to keep a charge but as long as it takes a charge it should be good enough to start the engine shouldnt it?

Check and see if the "starwheel" (reluctor)on the distributor shaft inside the distributor is cracked and slipping on the shaft.

Check and see if the "starwheel" (reluctor)on the distributor shaft inside the distributor is cracked and slipping on the shaft.
Thanks will check that when i am over at the garage on friday as im taking the Jimmy there to get the fuel pressure checked and the lil truck is over there where i had it towed.

Thanks will check that when i am over at the garage on friday as im taking the Jimmy there to get the fuel pressure checked and the lil truck is over there where i had it towed.

I am taking it a garage where they have the proper scanners etc to figure out whats wrong with it on Monday. There is a chevy diagnostics specialist there who is supposed to be good - i know its probably something stupid like a bad ground making the spark not quite strong enough or something like that but be danged if i can pinpoint it. ( this is a regular garage not my friends garage )

I agree, sometimes you just have to let the Pros have at it.

I agree, sometimes you just have to let the Pros have at it.
Turns out the 2.8 is fried as i have one cylinder with 70 psi and one with 90 so my next move i guess is to change to a 4.3L as a "good" 2.8 seems hard to find.
So............. if anyone has did this swap from 2.8 L to 4.3L in an 86 S15, What all do i have to change?
i understand that to bolt it up to the standard transmission (5spd) that is in the truck now i have to change to a 4.3L bell housing so will need one of those for sure. Can anyone tell me if the exhaust manifolds are the same and if the fuel pump for the 2.8 will work the same for the 4.3 and if i need to change the Ecm as well.
In general , if someone could tell me exactly what all i have to change to convert this over, it would be greatly appreciated as i dont know if the wire harnesses even work for the two different engines. Thanks in advance