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Losing Prime after VP44 install.

Old 10-26-2005, 05:52 PM
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Losing Prime after VP44 install.

I had my VP44 replaced a few months ago and noticed that they had an issue starting the truck at the dealership when I picked it up. I told the service advisor about it and he said that if it didn't clear to bring it back. Well I drove it 6000 miles and it still has the issue of losing prime after sitting for a few hours. When the tank is full I don't lose prime but if it's half empty the fuel system will lose prime. I bump the LP and it will run then I can start the truck.

So far I have checked to see if the filter is good and the cap is tight, looked under the truck at the lines and they looked good, tightened the hard lines going to the injectors and checked the line going in and out off the VP44. So now I am at a loss and the dealership won't look at it b/c the tech no longer works there and they don't have another diesel tech.

Bottom line anyone have a guess at what could do this? Everything looks tight. I've searched on this issue and a few guys said the fuel pickup in the tank but seems awfully odd that it would fail at the same time the VP44 was replaced. No issue with prime on the fuel system before.

-CM
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Old 10-26-2005, 07:07 PM
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I would say you have a leak inside the tank. You'll have to drop it and ensure there is no crack in your pick up tube.
That's all I can think of.Is there a check valve in the VP that might be defective?
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Old 10-26-2005, 07:13 PM
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I would suspect the fuel return check valve at the VP44. This is located on the side of the VP right beside the inlet line. I believe the inlet banjo bolt is 17mm head and the check valve banjo is 19mm.
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Old 10-27-2005, 10:56 AM
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So the check valve is on the outside of the VP44? I looked at the line feeding back to the tank but didn't see anything but a hardline connected to hose.

-CM
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Old 10-28-2005, 09:38 AM
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having the same problem, is there a check valve for sure? Wierd thing is if parked on an incline(front end up) it looses its prime, back end up its fine.
Is the check valve easily replacable?
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Old 10-30-2005, 09:08 AM
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10-4

I am haveing the same problem with my FASS suckin in air, all hose's/ fitting seem good, I did the human pressure test. so i think its inside the tank.dropping it soon.
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Old 10-30-2005, 11:28 AM
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Yes, the check valve or as some call it the overflow valve is on the outside of the pump. If you look at the side of the VP44, you will see 2 lines with 2 banjos, one with a 17mm head and one with a 19mm head. The smaller one is your inlet the 19mm head banjo is your return banjo. This banjo is actually a spring loaded check ball that allows your pump to keep a prime after you have shut the truck off. Without it, you would have to prime the pump everytime you started it.

Pretty much all that is involved is taking a 19mm wrench and removing the overflow valve out of the pump, flushing it out and verifying that the spring is not sticking or binding inside allowing the fuel to flow back to the tank. This can be checked by taking a small screwdriver and pressing on the spring to make sure it is not binding.
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Old 10-30-2005, 12:23 PM
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Overflow valves purpose is to provide some resistance to fuel flow, slow it down for the VP. I have never heard it having any bearing on a long crank time. You're getting air somewhere.
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Old 10-30-2005, 04:27 PM
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Originally Posted by J BODY
Overflow valves purpose is to provide some resistance to fuel flow, slow it down for the VP. I have never heard it having any bearing on a long crank time. You're getting air somewhere.
Check your troubleshooting symptom tree for "engine difficult to start" and you will see that a faulty overflow valve can cause a loss of prime situation just like the overflow valve on the P7100 trucks can.

This may not even be his problem, it could be an air situation, but IMO, I would check out the overflow valve.
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Old 10-31-2005, 06:12 PM
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Notice that I lose prime only after I the tank gets to approx. half full. I'll be taking the banjo out to see if it is stuck open. That sounds like the issue since the VP44 was replaced. Easy check.

-CM
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Old 11-01-2005, 04:13 PM
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Fix found

The last time I filled my tank I noticed that the tank seemed to be pressurized. When I opened the fuel cap it popped like it was pulling a vaccum. So last night after parking my truck I popped out and undid the fuel cap so that it would alllow air flow. This afternoon I started the truck no problem.

Now someone figure that out.

-CM
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Old 11-01-2005, 04:31 PM
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The cap is vented (correct?)
If this is correct how are you creating a vaccum on the tank?
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Old 11-01-2005, 06:48 PM
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Not sure if it was a vacuum or if it was pressurized. I noticed the pop noise so it could have been either. Usually a pop is from a vacuum sucking in air not a pressure pushing out. That's my reasoning.

I will test further to see if I leave the fuel cap on if the hard start issue returns.

-CM
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Old 11-02-2005, 08:25 PM
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Well the hard starting issue returned last night when I left work. Next afternoon on the way to work it started fine. Truck was parked on flat ground both times. I'm at a loss.

The cap wasn't the fix didn't make sense and was to easy.

-CM
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Old 11-02-2005, 08:52 PM
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At that point I'd remove the rubber section of line between the filter housing and the VP and install a long section of clear vinyl line. Put two large loops in the line. Run the truck, park it and let it sit....see if one of the loops developes an air pocket. That will some times give you an indication on which direction to travel for further diag.
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