Ran just fine one day turned it off, came back 15 minutes latter started just fine, put it in reverse started backing up and I could hear a buzzing noise, like a rely buzzing and the engine just shut off? Had a mechanic buddy come over with his tester, plugged it into the port and it said no communication IDM. So we pulled it over to his shop and ordered a new IDM. Then the tester said PCM was bad? So a few days later installed a rebuilt PCM. I left the Bully Dog chip out and now everything is coming on as it should and the injectors test out OK. Turns over OK and trys to fire on a couple cylinders but it won't fire up on all cylinders. Fuel pressure is at 65 PSI, replaced IDM, PCM, all fuses are good, both inside and under the hood, oil level is at full mark, turns over just fine, batteries are full. I'm stumped!!!!! Could the HPOP just go out? Put the big snap-on tester back on and no codes at all? I do know that if I don't plug it in at night it won't start in the morning. But we did plug it in for several days and still the same thing? Any ideas out there? Monday I am going to check the glow plug relay, and the glow plugs. Is there any electrical part that will cause this and not throw a code? Could it be the CPS just went out?

 

I will move your post to the 1999 up Power Stroke forum.
You will get better help there.