With your pressure guage, it's gonna drop once the pumps shut off. With no pumps pushing or pulling fuel there is no more pressure being generated, it's just static. The pressure guage is in essence reading vaccuum and with no pumps running their is no more vaccuum to read. So it's not telling you how much fuel is in the lines, just how much pressure you have in the lines.

Why would it do it all of a sudden though? Never messed with the injectors in it, never had anything off until the Vp got replaced. I would think that once fuel starts getting into the oil you would be able to smell it a little. I can turn the key off and truck wont even try to start on its own as soon as it shuts down. Everyone has told me once the pump kicks off it should hold the preasure at the Vp until it is started.

Were in the world do you have an oil analysys done?

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Ok but I thought that once I put a check valve in the line infront of the lift pump that it would allow it to hold preasure to the pump? I can clamp off the line before the VP and the guage will hold the preasure at 15 psi once the pump stops. I let it flow into the vp and it drops to 0 quicker then I can get back to the guage.

I think Heath on here can do analysys through AMSOIL or if you jut search the internet there's several labs that do it around the country. I'm sure some of these guys can tell you who does the best job for the least amount of money. They aren't expensive to have done though.

That new check valve/Banjo bolt is supposed to hold the internal pressure of the VP someplace around 14psi I think. I know it holds the pressure just not sure I'm remembering the pressure number right.

Correct the check valve holds 14psi of preasure and its new. My supply line has a one way check valve so you would think that is would hold atleast 14psi once the pump quits running but it does not. What am I missing here.lol

Check this thread, it has some diagnostic checks in it that might explain some of this better then I'm doin.

https://www.dieselbombers.com/showth...highlight=fuel

I know I got two bad check valves from the dealers. I ran a fuel regulator in place of that banjo bolt for quit a while because after that I didn't trust em anymore. I rigged up a tester and the one I got from cummins and from Dodge were both wide open by 4 psi instead of 14psi.

I'm thinking the diaphragm in the pump is ruptured.

If you pulled the fuel supply lines lose from the head when you were changin the pump that could be enough to cause a pump with the injector tubes. If you tightened them back down to much then it crushes the bottom end of them creating a leak, and it doesn't take much to do this. If they are a certain stock number many of the tubes used in our years of trucks were considered one time use and disposable. So if you take them lose you were supposed to replace them. Somewhere that stock number is listed on the site here but I would have to search for it. The tubes have it stamped on the side of them.

Since the truck is now gone but not forgotten, I am closing this one out.