Starts then dies

1989 GMC Jimmy 4.3 ltr 4x4 w/o anti-theft. Starts and runs for about 5 sec. then dies. Replaced fuel pump, pump relay, oil sending unit, distributor ignition unit. On-board computer diagnostics reads 'ALL CLEAR' no problems exists.

Replaced the in tank fuel pump. Drove it for about 3 weeks. After a 5 mile trip, went to start it & it would only start & run for 4 to 5 seconds. When it did finally start & run, it would stay running until I shut it off (30 min. or so). Then the same problem came back. Now it won't run more that 5 sec. Any suggestions?

Does it have good spark to all plugs?
Do you have good fuel prsssure?
Will it start or run with a snort of carb cleaner?
MT

Check the engine crankshaft sensor on the front of the lower part of engine.
It has one bolt and pulls out and has a wires with a clip towards bottom to un-clip.
it might be broken in 2 pieces, has a round metalic /w plastic housing about 3/4 " long.
If not broken still could be bad.
just ran across one on 99-blazer