FiTech EFI system

Just going to ask the obvious questions?

Is the red ( large) power wire hooked at the battery in the trunk? Is the white your keyed line? Almost sounds like your keyed line has a break( intermittent) like maybe in the ignition switch.

If the main power is to the battery, run a separate line from the battery to a temporary switch which you can turn on manually.. Might help isolate the issue. I got the white screen, once , when i did not have a proper feed to the main feed from the battery.

My Alternator is pushing about 14.7 when running, 13.9 at idle. I have my battery ground, running all the way back to the starter stud 0 gauge.

Sounds like your ground is fine. I have my battery in the trunk BTW.