Hey guys, it's been a while since I had been on here. Had some issues needed to work out with my health. Anyway here is what is happening to my 99 7.3. This all over the time frame of about 1 year.
I was having some hesitation under load, then it was having a hard time starting, enough that I would have to recharge batteries and re-fill hpop to get it to start, but once started and warmed up it would continue to start until it got cold again.. Thought I was having injector issues. I got some Hot Shot stiction oil change and Hot Shot fuel additive. This helped a lot with the hesitation under load. Now I no longer think I have an injector issue. However, yesterday I replaced the glow plugs and relay along with the valve cover gasket. Still had the long start issue, so I replaced the fuel filter yesterday, when I finished it started up great 4 - 5 times, this morning I get in to go to Home Depot for supplies, starts great. Stopped and started 3 times before stopping and filling up with fuel, once I finished filling with fuel and jumped in to head home it took about 15 seconds to start. Got home shut it down let it set for about 2 hours while I did my project. Went to start it and it would not start for 2 tries until the beeping started ( I guess about 20-25 seconds. I check the hpop and it is dry again, so I fill it, tried to start and it took 20 seconds or so but it started.
There have been no mods done to this truck! Help this is very frustrating to me.

 

Shouldn't be too hard to diagnose. Obviously your HPOP is draining somewhere and the options there are limited. There is a check ball in the top of the block right adjacent to the fuel bowl behind the HPOP reservoir. You could have something stopping that from sealing. Your other option would be injector O rings letting the oil drain down and a Cody test can determine that for you. You can pull the HPOP hoses off from either end and pressurize the HPOP rails and listen for the gurgling. I do not know if they low pressure oil pump could cause those problems or not but someone else will probably be along to address that if it could be the culprit.