Re: replaced pump won't run unless you prime throttle
I assume that you mean that that you have to keep your foot on the gas pedal to keep it running if this is the case I would replace the idle air control solenoid or IAC as it mostly called it is a ez fix it is located on top of the engine in plain site with two 8mm bolts it will take about 10 minutes start to finish, again I am saying this with the above guess if this is not true I will need more info.
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by primed are you supplying a fuel source if so then the car is not getting fuel to burn. this indicates your fuel pump is bad and needs replacing and change the fuel filter also. the reason the pump won`t work sitting overnight is that the pump can`t build up enough pressure possibly because the fuel pressure is not being held, but after the first start up the system can maintain enough pressure to start through out the day. you can have the fuel pressure and volume checked with a gage when the problem occours to verify.
there is a fuel pressure regulator built into the throttle body on the engine. the fuel tends to bleed off pressure before the truck starts if the regulator is bad. parts stores offer a kit to repair the regulator.
If you turn the key to the on position and you hear the fuel pump run, does it run for longer then 5 seconds? If so then you are going to need to look at your fuel filter, if it stays running then you are going to need to look at your fuel regulator. You can also go to Auto Zone and buy a fuel pressure test kit or rent one, and check your fuel pressure on the fuel rails. Check for spark also, if you are low on spark then you are not going to fire, unless you dump more fuel then you need to into the throttle body.
you can attempt to run it w. starting fluid to make sure the engine is running aside of fuel issues. You may need to replace the fuel filter/regulator if it is a single piece. If it's definitely not getting fuel, its either a pump/filter/regulator issue, or an electrical issue. You can generally hear the fuel pump running when the engine is on if you are close enough to it. you can almost always hear it prime. if all is good and the fuel pump can be determined to not be at fault, change the filter and try again.
Sounds like the fuel pressure regulator is allowing the fuel pressure to bleed down. While sitting (key off) it should hold about 30 psi of fuel pressure to keep the system primed. When it bleeds down it causes an extended start, you sometimes have to cycle the key a couple of time before it will start. If this is the case then replace fuel pressure regulator. FYI pumping the accelerator on a fuel injected vehicle does not prime the system.
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.