The 6.9 should have C.I.S, right?
If so, you are either loosing residual fuel due to leaking check valves or it's bleeding off through a leaking injector.
You may also have a problem with getting power to the fuel pump during cranking. The pump will only get power when the key is in the start position or if the air plate is moved down by air flowing into the engine.
One way to do a quick check would be with KOEO, press the plate down for a few seconds then try to start the engine. I'm willing to bet it will start right up. Don't leave the plate down too long as you will flood the engine, don't ask how I know this
A different method, which may or may not work is to put it in drive and crank the engine for a bit to see if you can build up fuel pressure.
I have the
JC Whitney fuel pressure tester and very much recommend it or one like it.
If you don't have C.I.S., well then, just ignore me.
Michael