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If fuel pump is stock then it turns on as soon as the key is in the on/run position. Is pressurizes the fuel bowl and galleries/fuel rail for about 8-15 seconds.
You can open the drain to the fuel bowl (yellow arm on back of fuel bowl that moves 90 degrees to open) and put a piece of 3/8 tubing on the metal tubing where the fuel drains to under the engine and direct that tube to a 1 gallon jug or a pail or oil drain pan and turn the key on OR have a friend/family member turn the key on for you while you watch the flow from the tubing to verify you have flow. Have your friend/family member turn the key off when you are satisfied that the pump is pumping. Then close your fuel bowl drain back and then cycle the key on and off a few times to get any air out of the fuel bowl so it does not go into the fuel galleries and get into the injectors. The pump will probably not shut off because it will not get up to the 50-55 PSI that the regulator is set for. Play it by ear, keep your eyes on it and try not to overfill your catch container so you can re use the fuel.
Dwayne
It sounds like the issue of it dying out of the blue like you turned the key off is the camshaft position sensor. There's a recall for my truck (2003 7.3L) and it was dying out of the blue at random times, each time it took different amount of time before it would start back up. Eventually it died and wouldn't start. Towed it to dealership, replaced CPS under recall, started up and had no issues after that! :-)