Will only start if you prime engine with fuel

Possible defective low pressure fuel pickup pump inside the fuel tank.

Hello there , sounds like your fuel pressure is low , your fuel sensor may be faulty or your fuel pump is sucking air from between the pump a fuel tank .. Regards Graham ...

sounds like your fuel pump weak, need to check fuel pressure when engine won;t start and check with engine running

If you're referring to a fuel injected gasoline vehicle, self prime takes place at key start. If you still feel the need to have the computer repeat this process (or re- self prime), turn the key all the way until the dash lights come on, then turn off. Repeat this 5 times then attempt to start. If all the windows are closed and the radio is off, when you turn key on with engine off, you'll hear the fuel pump at the rear of vehicle buzz or hum as it's priming the system.

Turn the ignition key to the ON position without starting the engine

You should hear the fuel pump priming for about a few seconds then shutting itself off.
If not hear replace the engine oil pressure switch
The 3rd wire to that switch is the pumps prime switch lead.
When the engines oil pressure is reached the computer will shut that circuit off and turn on the fuel pump relay
If you hear the pump prime the relay maybe at fault instead

The fuel pump might be working but it is not priming. When you turn on the vehicle, the pump sends fuel under pressure to the injectors, to "prime" or have fuel present to be able to start engine. Without it there will no fuel available to start it. You are manually priming the engine, and the fuel pump is taking over from there. Check connections to fuel pump and replace if necessary. It is not an inexpensive repair

cant lose prime...it gets primed everythime you turn the key off and back on for more than 10 seconds.

have you had the coil pack controller checked?

any Check engine light when its running?

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/sean_54c3a3dc48a7773c

There is a check valve in the fuel pump that sounds like it may have gone bad. Check the fuel pressure at the shredder valve, there should be 60 to 65psi during the prime and will drop 5 psi when the engine is running. Once the fuel line is primed, check to see how fast you lose your prime. Since you replaced your injection system, we can eliminate the fuel pressure regulator leaking which was common on the injection system your truck run's on. If the fuel pressure drops fast then it's going to be a bad check valve at the fuel pump and it may be time to replace the fuel pump it self. Good luck and hope this helps. Note: do not try to start the engine with putting gas through the throttle body, it's been know for small fires to start and burn the spider injectors. 

defective fuel pump the check valve is allowing it to lose prime replace fuel pump.

i have the same problem on a 98 jimmy 4.3 4x4.
i replaced the fule pump and have good pressure.
new wiers & coil (good spark) no MIL & no codes.
will only start when primed. it will run & drive all day
with no problems.
but once it has been turned off (warm or cold) i will
have to prime it once again to start it.
i have another engine that was in it before it spun a bearing.
it ran fine so i know all parts are good.
i swaped the mass air flow and throttle body but i still have
to prime it everytime to start it. am i forgetting something?
should i swap out the intake with the injectors?
any help would be sweet. thanks.