Engine Performance problem
1990 Other GMC Models V8 Four Wheel Drive Automatic
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1990 suburban. 5.7 auto. TBI
Cranks, and almost catches.
Sometimes catches and stumbles for a few seconds
Lots of black smoke when it stumbles
Adjusted timing, no go
Checked plugs and gapped.
Checked cap and rotor are good.
Checked for spark, lots of spark.
Confirmed all spark plug wires are routed to correct cylinder
Fuel can be seen spraying well into throttle body.
Exhaust is not plugged.
No loose vacuum lines or broken wires observed.
I am wondering if the timing chain has jumped a tooth? Only thing I have not confirmed is when #1 is at TDC if rotor is pointing at #1 plug wire.
Any other help is appreciated.

unplug both fuel injectors and see if it will run. also check the egr valve to see if it is stuck wide open. black smoke indicates way too much fuel. are the plugs gas fouled?

I verified that the egr does move, as it is not stuck in any one position.