My 2000 f350 7.3 will not fire off on its own. This just started one afternoon. Drove in, shut it off then no start.It turns over and nothng. I put just a small amt of spray into the filter, and I mean small, and it fires up and runs till you shut it off again. Could be all day or whenever. Idles great and runs like nothing is wrong until you shut it off and your back where you started again. Replaced the cps. Nothing showing on the dash, like eng light etc. If you shut it off and quickly restart it will go, but not if you let it sit for a say 5 min.
What is your best guess?

Perform the tests in the link below:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-8.html#post1415281

Be sure to test the glow plugs and ensure the oil is filled to the FULL Line and that it has been recently changed. If the problem persists, check the oil pressure with a known good mechanical gauge.