I just replaced my VP44 and had no problems losing prime until it was replaced. I tightened down the 3 injection lines to head all the way tight and left the other front 3 loose to bleed air. Cranked a couple times after bleeding line into pump and i got fuel at number 1 then fuel at 3 and then fuel at2 and it started. I drove it up street and turned around it ran great, pulled into driveway and shut it off and an hour or so later it wouldnt start. Cranked and cranked till it reprimed and started and ran great. Shut it off overnight and it did same exact thing. Let it sit some more to try it again and cracked open injection lines and i saw it bleeding the air out closesest to head. It wont do it if it sits for under 20 minutes, but closer to an hour its hard to start. Never had this problem before replacing pump. What can cause it to lose prime this quickly? my best guess is that relief valve on the side of the pump? I pulled it out and checked it and it was fine. opened under pressure. Could I have hurt this relief valve by cranking it down too hard to make it tight?. Where can i buy one at? I tried kunkels and they said" a what" . I cant find any leaks on the exterior of the motor. All injection lines to head are super tight and dry. All lines on back of pump are tight and dry. I appreciate everyones ideas, truck is stuck with trailer on it in my driveway. SOrry for such a long post

 

did you put a new lift pump on it too, may not be your problem now...but it is most likely what caused the vp to go out....the stock LP suck. Check all your lines in the fuel system and make sure the fuel filter housing o ring is seated right.


If you fill out your signature it can help us in troubleshooting problems because we know any mods you have done to your truck

 

Hey Josh, If I was a bettin an I would bet that the problem is the lift pump. The lift pump has a check valve in it that keeps fuel from flowing backwords through it going back into the tank and also acts as an internal pressure regulator. If the pump is bad that valve may be worn out. The Lift pump going bad is also the major reason the VP44 goes bad. The LP is not supplying the enough fuel to the VP44 and it overheats the electronics or cracks the diaphram in the pump.

So hopefully you have a fuel pressure gauge installed, if not you need one ASAP cause without it your risking having to replace the VP44 again. The fuel pressure should never fall below 7psi no matter how hard your pushing it. Keep in mind that if your lift pump is not working right this new VP44 will not last very long at all so this is important to check.

Right now odds are pretty good that if you have a guage it's either sittin at 0psi at idle or falls on it's face and goes to 0psi as soon as you hit the go pedal.

 

Or possibly a leak between the connector tubes and injectors. small leak anyway. All leaking fuel would just return to the tank.

 

he asked me about this being a possibility but in my past anytime this was an issue it would leak fuel into the oil and over fill the oil pan. Not to say that I'm right by any means.

I'm still bettin it's a bad LP lettin fuel run backwards in to the tank after the truck is shut off.

 

this wouldnt put fuel in the oil. It will just return to the tank. It is just suspect that it happened since installing a pump. It is possible to overtighten the lines at the head also

 

Any updates?

 

Since there have been no updates in so long, I'm going to assume that the problem is fixed and am closing this thread. The thread can be re opened if needed.