I've got a 2000 chevy Blazer 4.3. I've replaced fuel pump, fuel filter, plugs,wires,cap,button,distributor,the spider fuel injection system, ignition switch,and key. Everytime I try to start engine it will crank and die, crank and die. But as long as I'm pouring gas in it it will run perfect. I've checked everything there is to check and all is good. Fuel pressure good, firing great, what could cause it not to run on its own.

 

Welcome to the forum!

What could cause it not to run on its own? With symptoms like you describe, Passlock is the first place to check.
Does the "Security" light in the instrument cluster illuminate when you initially turn the ignition to the "RUN" position, (before you attempt to start the engine)? After a few seconds, does it shut off, flash, or remain illuminated?

Here's something to try:
Apply battery voltage to the fuel pump prime
terminal in the underhood fuse panel.
The fuel pump must activate and remain running.
Attempt to start the engine.
Post your results.