Lift pump will not draw fuel from tank? Does it self prime?

[waynep]

Hello All:

Replaced lift pump with a new unit, and while replacing most of the fuel drained out of the input side of the pump fuel line. Replaced pump, and new pump would not pump fuel out of the water drain valve, even after running for 10 minutes or so by powering pump test connector.
I had to disconnect supply side of pump, suck fuel into supply line, reconnect pump and then bleed air out of system OK.

I thought the lift pump should have self primed? Does this also mean that I have to do this again if I were to run out of fuel?

Supply line to tank OK, but could their be an issue with the fuel pickup in the tank to cause this? New tank and fuel sender unit less than 4 months ago.

Thanks, Wayne 1997, 3/4 T, 4 WD Sub.

[DmaxMaverick]

It should self-prime. If it isn't, you might have a leak between the pump and tank, and it's sucking air.

If you find no leak, and you just have a temperamental pump, you can use low pressure shop air (~5 PSI) at the tank filler, or suction at the water drain, to help it get primed. It should sound different once the fuel hits it. Once the pump gets "wet", and pumps well for a while, it should do better next time, if need be.

Otherwise, you got a bad pump right out of the box. Rare, but it wouldn't be the first time.

[waynep]

Found a kink in the return fuel hose inside fuel tank that almost totally blocked the return fuel line. Removed kink, but too early to tell what effect this will have.

Any ideas appreciated, and in any case, what does the return fuel line really do?

[JohnC]

what does the return fuel line really do?

Exactly what you might expect. Excess fuel bypassed by the injectors or the pump is returned to the tank...

[waynep]

Hello All:

Well it ran ok for about 150 miles and then, back to the same old problems, minimum or no fuel flow. I think that I Have tried everything except replace all the fuel lines.
Have not checked the return lines.
If the return line was blocked, what would happen?

Thanks, Wayne

[Warren96]

It sounds like it could be an air leak on the supply line between the tank and lift pump. Does the fuel line look damp or wet in this area? Is the tank full? Can you hear the pump running ? Does it leave a small fuel puddle under the truck after you park overnight?

[waynep]

Please see my other post for the solution to this puzzler. Would never have believed that a new fuel line that would pass low pressure air would only partially pass diesel fuel.

Thanks to all, and GM parts can go pound dirt.

Wayne