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Are you talking about an electric pump? Personally, I am a big supporter of the Cummins mechanical pump with the primer button. They have always been good to me. Sounds like you have an air leak somewhere between the tank and lift pump. There are check valves in the lift pump that should prevent drainback. Have you tried bypassing the metal fuel line using a piece of rubber line from the tank to the mechanical pump? The metal lines have been known to develop pinholes where they rub retaining clamps or body/frame. If your drainback problem goes away, then you know the metal line is the issue. You can use clear plastic line to bypass hard lines and look for bubbles too.

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check your fuel filter, gasket, center bolt oring, check the change ocer valve, most of these and the lines to it, tend to leak, change ALL the lines, rebuild the change over valve (tank draw switch valve)

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I edited my post, even with NEW filters, CHECK to make sure the o-rings are seated correctly

I don't think the added pump would hurt . It may even help you find your air leak , and may also act as a check valve keeping fuel from running back into the tank .

I find the hoses around the change over valve go first. Try presureizing the tank 2or 3 psi. and the leak should become visible.

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If you put in a pump you are going to have positive pressure......where ever the system is sucking in air you are going to have fuel leaking out.......this can cause all kinds of problems.....not the least of which is attention from the environmental zealots.

If you pressurize the system slightly and get some soapy water in a squirt bottle you should be able to find the problem by spraying each joint......you may even be able to hear the air hissing out if you are in a quiet place.

wreckerman893 said:

......you may even be able to hear the air hissing out if you are in a quiet place.

Click to expand...

I don't believe such a place still exists...

Derrickl112 said:

Is there any reason why this would be a bad idea? My truck wont stay primed and I have been unable to find the problem. Re-soldering the pickup tube helped alot, but when the truck sits for a day the fuel drains back down to the tank.

I already have most of the parts needed, but wanted some oppinions on it.

Is there a reason why a fuel pump was never put on these trucks? The small hand pump sucks!

Click to expand...

Derrickl112, You may look at this thread.
I had a prime problem and it was the pickup tube in the tank.

http://www.steelsoldiers.com/5-ton-up/79327-m923a1-losing-prime.html

I say do it. With those cheap pumps on that one site, you have nothing to loose.

I did it on a old 7.3 diesel pickup and it was great !!!

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It was wroth a shot. Good luck with your pump.

What type of pump are You planning on using? I have thought about using a MEP-003a 24 volt pump?

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hey derrrick what if you just had it for startup and then shut it off when running ??

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