Update on 5.0 starting problem
 

A few days ago I did a post on my F150, 5.0, 1993 not starting....

Now I was finally able to get it started and pull a code..KOEO Code 556 ....Thermactor Air System Fault...or "Primary Fuel Pump Circuit Fail"

So I am able to start the truck with a couple of squirts of ether in the intake air filter.....the engine starts rough idle, engine light on...so now drive it 1/8 mile and light pops off...and the engine smooths out...runs like a ***** cat!!!!
Run it all day with r two dozen start-stops no problems...
Now let the truck sit for 8 hours and your back to square one....

However since the truck will start with ether, I thought that maybe the fuel-injection system was not getting that 1 second prime as you turned the key on...
So after sitting for 10 hours I tuned the key on for 10 seconds, heard the pump come on..I shut the key off.....then it started on the first crank....running smooth and no engine light...
Now..Is it a Bad fuel pump on this dual tank truck????, but the pressure on both tanks was spot on...???? What controls that 1 second spurt when you turn the key on....
Idea's..??
Crackers...

Thinking there's a check valve somewhere that isn't holding, allowing the fuel to drain back further than the 2-second prime cycle will bring it back up. Never got real ambitious to find it once I found that rolling the key to On a couple-three-four times before going on to Start solved the problem.

I have a 95 150 with the 5.0 and this sounds like my truck. It will run just fine and then I get in it try to start it and it will turn over but not start. I have replaced the distributor cap and rotor, the wires and spark plugs, and the ignition module as well. I am lost. When I turn the key I hear the fuel pumps kick on. It also will occasionally die while driving and I let off the gas. Both tanks where dropped, cleaned, and two new fuel pumps were put in a little over a year ago.