99 Expedition shuts off istantly.Help!

I have a 99 Expedition with the large motor and 80000 miles on it.I drove the truck and it ran fine and then i parked it for about a week and when i went to start it the truck starts for a split second and then shuts right off this happens everytime i tried to start it.

Go out and turn the ignition switch to the run position so all the dash lights come on, but don’t try to start the engine. Leave the ignition switch in this position for two seconds and then turn it to off position. Repeat doing this a half a dozen times, and then try starting the engine.

If the engine starts, the fuel system just needed to be primed.