[stacked cummins]

Ok so here is the story. I bought a 99 3500 with 130k, the kid/guy i got it from had no idea how to wrench on the truck. i have dealt with a couple of these vp trucks and know my why around them. i got the truck home and changed the starter, and it wouldn't start so i primed the system cracked the banjo bolt on the side of the vp and got a good prime tightened it up and it started up. i noticed a couple of the fuel lines had a small pin hole so i replaced those and re-primed and it ran great. for the passed two weeks while working on the truck it would start up but run rough. i changed the fuel filter and i noticed that the filter housing was half full of water. so i pulled the tank and drained all the fuel out and got 3.5 gallons of water out of the tank. the best part was the fuel looked like lemonade not the bluish color diesel normally is. put the whole system back together and and now i can get a prime i will tighten the banjo up and i can hear the fuel go back into the tank and the system will loose its prime... so today i replaced the lines from lp-filter filter-vp thinking there could be another pin hole or bad banjo bolt washer. same thing back feeds into the tank.. so i i have a jumper wire for the lift pump so i set up a 5 gallon bucket full of diesel next to the truck and ran a hose from bucket to the lp with my jumpers to the battery got a prime tightened up the banjo bolt and same thing. (doing this eliminated the chances of the line from the tank being bad or the lines in the tank being bad.) no i replaced the stock carter pump with a raptor pump that i had laying around. got a prime and same thing happened. replaced the filter thinking it could be an oring still did same thing. swapped the filter housing with another i had, same thing got prime and then as soon as i take the power from the pump away all the fuel drains out of the lines and i loose my prime. each time i will prime to a constant 12-15 psi get a steady stream of fuel from the return line off the side of the vp. i have started the truck up and it will run fine now with good fuel and as soon as i shut the truck off i loose prime. no leaks and no noticeable leaks or puddles with priming or running or sitting. i replaced the gas cap also and every line fitting and o ring of the fuel system... so before i set fire to this truck someone help my head hurts from doing this all day

 

[smokin_dodge]

If your losing prime in the LP fuel system you are introducing air into it somehow. If you have replaced all the fuel line, I would check the banjo bolt o-rings as well as the fuel filter housing o-ring and valve.

 

[stacked cummins]

i have replaced all the o rings and checked banjo bolts and replaced filter o ring and the actual filter housing

 

[smokin_dodge]

Well the only way to lose prime is by having air to break the vacuum, or a greater vacuum in thr tank.

You could try a fuel UV dye to locate the leak.

 

[dozer12216]

When you replaced the Fuel lines to injectors, the orings on crossover tubes were damaged.
A test for air leaks into fuel system causing loss of prime is: Park the vehicle downhill with at least 11/16 or more fuel in tank.
If does not lose prime your problem is: Banjo bolt at back of head is leaking. The 3 way connector in same area is leaking. Or the injectors crossover tube O rings are damaged. Other self induced issues can also cause. do not have the capability to imagine all the possibilities.
It sounds like you have a fairly large leak. Try pressure the fuel tank filler.Wrap a rag around air gun and VERY lightlly pressure the fuel tank. 3-4 PSI is all need...

 

[Mopar1973Man]

I would follow Dozer's suggestions and report back with your findings.

 

[stacked cummins]

ok everyone i took the truck lifted the back of it about 9" on a jack and jack stands primed the system started the truck up ran great started right up no lose of pressure stayed at about 14 idle... then... shut the truck off lost prime i looked at the banjo in the back and the o rings and both look good so any other ideas?????

 

[jakeandkatiesdad]

VP overflow valve?

 

[Mopar1973Man]

VP overflow valve?

Overflow valve has a permanent hole in it so it don't count.

 

[stacked cummins]

i ordered a new overflow valve also ordered a check valve to put in line before the lp just to see if that will work. the air leak i am having is not slow like a valve but like there is an open end somewhere or almost like a straw with your finger on the end and take your finger off the other end..

 

[dozer12216]

9 inches is not much of a downhill... with 11/16th or more fuel. Reread #5 post and do rest of tests. 3-4 psi into tank should show a leak real quick. If it lose prime that quick. Or perhaps you have no clues..

 

[jakeandkatiesdad]

Overflow valve has a permanent hole in it so it don't count.

But in your testing procedure you say something like it is the last sealing point in the fuel system before fuel leaves the IP. There's also a guy on one of the forums who changed it and his lost prime issues went away. :confused013:

 

[stacked cummins]

okay everyone i have figured out my problem. so after draining the tanks and putting in 15 gallons of fuel the fuel level was lower then this piece of the sending unit that was in the tank. so i took this piece out got a 3/8" line and drilled a hole into the bottom of the sending unit so ts like a draw straw type set up. it holds a prime so i think the metal ring was not holding a seal and with the ring above the fuel level it was taking air from the tank and making the system loose its prime. i did this all this past weekend and then yesterday i went out and the truck fired right up. arty018: thanks everyone for the help.