Will not start

Hello,

So does it crank and not start?
If it cranks but not start then it could be fuel related. If it just clicks with no crank they it could be a battery or starter issue.

https://www.2carpros.com/articles/car-cranks-but-wont-start

You will have to check to see if you are getting spark to the plugs. If you have spark then you will need to check the fuel pressure.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Can you hear the fuel pump come on when you turn the key to on position?

Let me know.
Thank you.

It's a diesel flatbed. It cranks. But i'm losing fuel pressure. I'm wondering if I have a check valve stuck open just don't where to look at.

Right, it uses the Ford 7.3L diesel.
Usually if the engine cannot sustain fuel pressure it might start but will stall after a little bit as soon as the pressure drops off.
If the pump is strong then it could be the fuel pressure regulator.
Unfortunately I don't' have access to the International truck repair catalog to provide you with the diagrams.
But if the regulator is weak, it won't be able to sustain the needed fuel pressure.

The pump doesn't stay strong.

Do you know where the check valves are located at?

Where is the regulator at?

On a F450 7.3L (sorry I don't have diagrams for the International trucks) it is located under the engine cover (see diagram below).