Calling all 7.3 experts....1999 F250 S/D with odd habits!

[WildMike]

I have a conundrum that is driving me slowly around the bend...

My ol Faithful has been getting moody, and here be the symptoms;

If I don't use or fire up the unit daily, and let it sit for more than a day it absolutely doesn't want to start. Yet it I have drove it to work and let it sit all day, 8-12 hours outside in the winter in -40 and she fires up like I just shut it off a few min ago.

I run 0w40 full syn oil all year round, and keep up on all maintenance like a stickler...always making sure the air and fuel filters are changed every 2-3 oil changes, and I like to run diesel fuel conditioners regularly.

The ol unit has 2 new big Ford batteries, a new starter, alternator, new glow plug solenoid, camshaft position sensor, and a ton more recent new goodies.

Now an interesting thing is, it can sit for a week, and if I plug it in overnigh it fires right up immediately. Yet if not it just cranks and cranks and cranks...
The glow plugs all tested well and seem to be working. There was a time about a month back and it was well below freezing, and my block heater wasn't at that time working, and I had to resort to the either fairy...a few days. It fired up on the either but it took a fair bit of fogging before the engine would run on it's own steam, so to speak. Kind of like the fuel siphoned back to the tank and had to pump back up to the injectors...

Ol' Faithful has at this time 487,xxx.km's and still pulls like a freight train, and runs smooth as the come when it's warmed up!

Now...any ideas?

[WildMike]

Anyone been down this road...?
Any similar cases?

[JSchuricht]

Rig up a light on the GPR to see if it is working intermittently. Get a scanner and check IPC during startup. Setup a fuel pressure gauge to see if you still have pressure when cold..

[WildMike]

Ok, sounds good & will do!
And I'll post results...

Thanks!