98 K1500, 5.7, 135000 miles. Runs great, idles fine, plenty of power, no issues at all- except it will not start after sitting for three or more days. It seems to hit on a cylinder or two, but that's about all. Letting the system prime by leaving the key on for a minute or so has no effect. But pouring a little raw gas in the air horn fixes the issue immediately- fires right up and starts just fine every time after that, no problems whatsoever- it starts right up, no matter how many times it's started that day and even the next day, but if it sits a while, no joy!
Fuel pump is a couple years old. No fault codes found, either.
Anyideas?.?

 

Newer fuel pumps do go bad especially if an aftermarket cheap one was installed. It pays to use only Delco or Delphi pumps considering the labor involved. It does make a difference, they do last longer. Check your fuel pressure.

 

Since the engine gets enough fuel at all other times, i'm at a loss to understand how the pump would cause this, unless there's a check valve built in that is letting rail pressure slowly bleed off. Is there such a valve? Even so, letting the pump run for a few seconds should be enough to reprime the system. Also doesn't explain why it starts instantly if the air horn is manually primed. I suspect something with the computer, but that's just a WAG!

 

There is a check valve in the system. How does the computer know that the system is primed? I added a check valve in the fuel line of my 99 Silverado and my problem went away. It started instantly everytime.

 

That's good input, kinda goes along with my thinking. So- where'd you get it, what kind, and where did you put it?
I think the computer doesn't knowthat it's been primed, but it does know that the egine is running and then tells the fuel pump to do it's job, in other words it goes from start mode to run mode. Maybe!

 

I got the check valve on Ebay. It has to be one rated for fuel. Also need fuel hose rated for fuel injection and 4 hose clamps. I put mine near the fuel tank. You will need a small tubing cutter to cut the fuel line and that is it.