I can drive my 93 6.5 with a manual fuel pump as far as I like with no problems. I can shut it off and restart it with no problems. If I shut it off and come back say 3 hours later, no problem. But if I shut it off and come back an hour later, I have a hard time starting it. The engine sometimes will start up, and after a few seconds start missing and then die. I hold the pedal all the way down like I would with a flooded gas engine, and crank it over. The engine turns freely for awhile, then the fuel seems to pick up, the engine starts with a miss, and then slowly recovers and runs smoothly again. Any ideas what would cause this, and how I can fix it?

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I've changed the electric fuel pump and filters, but it doesn't seem to make a difference. Could the fuel be getting hot and not flowing, like an old gas engine vapor locking?

 

Sounds like the IP is worn out.
Once worn the starter can't spin the engine fast enough for the IP to build enough pressure.

Next time this happens pour some room temp water over the IP to shrink the housing a little and try again-if it starts easy you know your IP needs rebuilt or replaced.