Lift Pump Problem

[n0n0_1963]

Hi guys, I'm running out of patience in the installation of a new lift pump.
Here is the story, two weeks ago when I start the truck the rpm was going up and down by themself, I took few minutes before the problems disapear. In the past I never had any trouble starting it cold, only when it was hot, few more crank was neede when it was hot.
Anyway when I came back from my trip the truck start right away but dies a minutes after on warm up. I cranck the motor and no fuel was coming from the filter air drain port.
I change the fuel pump but this one wouldn't prime, I pressure the tanks and got the fuel thru the filter but when I cranck the motor no fuel. I remove the new pump and check it, wacuum is good, I check the rod and this one is moving when I turn the motor by hand. The problem is every time I prime the pump ( suction or pressurize the tank) the fuel go away.
Should I do be able to read any vacuum when I cranck the motor ?. Since the pump is the latest model model should the fuel going back to the tank?. I took the pump three time out already and with a banks on it it's quite and experience.
WHAT COULD BE WRONG?

[DmaxMaverick]

This is a mechanical lift pump, right? It should show vacuum when cranking (it is a simple diaphram/check type).

sounds like the push rod is not engaging the pump arm. It is possible to install the pump and have the arm miss the push rod (along side it, rather than on it--ask me how I know). It can be a real pain to install it in the vehicle. The rod falls out. How did you keep the rod up in place while you installed the pump? The best way is to use a generous amount of bearing grease to get it to stick up in the fully retracted position, and make sure the pump lobe is away, not on the push rod.

The new pump could also have a mis-shaped pump arm, not allowing enough engagement to pump.

Get us a little more info on it.

[n0n0_1963]

Thanks for the reply, I install the rod back with some heavy grease and this one is staying in place, the pump is mechanical, I rotate the cam to have the rod the maximum inside, I'm ready to re-re-install it. When I removed the pump the second time it doesn't even show trace of contact with the rod and I start to think the lift pump has a incorect arm, do you ever hear about this problem.

[arveetek]

I've seen and heard of broken pump rods. Are you sure the rod is one piece and of the original length?

Another thought is that you have a cracked fuel hose between the pump and the fuel tanks, allowing it suck air and allowing the fuel to drain back to the tank. Most likely it could be the rubber hoses at the top of the tank itself.

Casey

[Sawz]

I had the exact same problem with my 83 K2500 I even kept my finger in the hole and checked the throw of the rod. my only guess was the rod was not original or the lobe it rides on was worn either way I got tired of screwing with it. I put a gasket and cover over the hole and installed an electric fuel pump back on the frame just after the fuel line crosses through under passengers door runs fine now

[n0n0_1963]

I found the problem the new pump was bad from the factory, the parts store exchange it with doubt, I install the new new one and voila, damn bad luck !!!.
I got a lesson out of it. Never trust new part 100%, Thanks for your help.