Fuel system losing prime

[olred92]

My truck has done it twice now. The other night I started it to go to town and it took three times cranking to start and they were long cranks like 15-20 seconds. notice that my WTS light was not on so I thought it was just the cold air cause it was 20 degrees outside. It started fine all other times that night. Started it to go to town again today and it did the same but WTS was on and it was 51 degrees today. I believe that the fuel system is losing prime. Was wondering if anyone else has experienced this. I will go out in a couple hours and see if it takes overnight or if it will do in a few hours. Truck has been sitting for almost three hours now.

[98whitelightnin]

Park with the nose down hill, if it starts good in the morning you need to start tracing a leak.

[olred92]

Would the transfer pump be a good place to start?

[Mopar1973Man]

More times out of ten the suction line from the lift pump to the fuel tank is where the air leak starts at typically. When it does develop a air leak the fuel never leaks outwards and typically will have dry lines and no sign of problems. But now pressure the fuel system and now you'll see the wet spots form. What I suggest is get the truck running and pressure the fuel tank with 1-2 PSI of air through the filler neck and then have a partner crawl around looking for the wet spot. Reason I suggest having the truck running is if the fuel suction line is leaking air in that means if you pressure the fuel tank it may or may not run fuel back out. But if the fuel system is flow to and from the engine and you pressurize the system it should show quickly.

[olred92]

Mike you just reminded me that I pulled my fuel cap off when I got home and Idk if the tank was pressurized or had a vaccum on it but there was a large amount of air movement when I pulled the cap.

[oldschool]

Large amount of air movement doesn't sound good. Maybe the tank isn't vented right. Try loosening the cap before starting. The WTS light SHOULD have been on. Your air intake sensor may be unplugged corroded or bad. The computer takes this reading and alternates between heater relays on energize output.

[olred92]

Large amount of air movement doesn't sound good. Maybe the tank isn't vented right. Try loosening the cap before starting. The WTS light SHOULD have been on. Your air intake sensor may be unplugged corroded or bad. The computer takes this reading and alternates between heater relays on energize output.

The light is on now. The other night I had found one of my battery cables vibrated loose so I think that is why the light wasn't on then. It has been on everytime since I put the cable back on. And now that I think about it my IAT is plugged in because i can read the temps on SG2

[oldschool]

Good news on the WTS light. I forget how my module is vented but it should not be a large pressure vacuum difference. Try with the cap off to start.......Good luck.

[JAG1]

I had this problem once and found my factory filter cap was not torqued enough. 25 ft. pounds is all. It's plastic so check for cracks and the O ring is on there correctly. When you tighten the filter cap you gotta' use the big socket not the center square part. That's how some have cracked in the past.I added my own tank vent because some factory vents have clogged in the past.Just a shot in the dark

[olred92]

I just went out and the truck started right up after sitting for approximately five hours. I took it for a 20-25 min drive and made sure that it got to operating temperature and then drove another 5 min or so. I drove at slow speeds and at highway speeds also. When i got back home I removed the filler cap again and it moved a large amount of air once again. I believe the tank is being pressurized:think:. I will see what it does in the morning when I go to PT. @JAG1: The filler cap is only a month or so old because when i bought the truck they had a locking cap on it which was nice but it was a PITA to deal with so i replaced it with a brand new from Autozone. I'm not saying that isnt the problem as I know how some parts can be brand new and be worse than the one that came off lol.And the record to all its a little harder to drive stick in house shoes when my seat is set for when im in my work boots lol:duh:

[Jesnic]

Add a fuel pressure gauge and airdog, raptor or fass. With the comp box and running the stock lift pump, it is just a matter of time before the lift pump can't handle the amount of fuel the comp box is requiring. Next thing to go will be the vp44. Not cheap. Could also be the ball detent valve in the vp44 pump not functioning properly and not allowing the fuel to return to the tank, therefore pressurizing the fuel line back to tank.

[olred92]

Add a fuel pressure gauge and airdog, raptor or fass. With the comp box and running the stock lift pump, it is just a matter of time before the lift pump can't handle the amount of fuel the comp box is requiring. Next thing to go will be the vp44. Not cheap. Could also be the ball detent valve in the vp44 pump not functioning properly and not allowing the fuel to return to the tank, therefore pressurizing the fuel line back to tank.

I just broke down and ordered guages a couple hours ago. Got the three guage pod with a 1500 EGT, 30PSI fuel pressure, and a 60PSI boost guage. Paid 227 and got free shipping, dont believe it was a bad deal but we will find out soon:shrug: Was looking at a 3/8 big line kit from filter to VP. Any suggestions???

[Jesnic]

If you ever add bigger sticks or need more fuel, 3/8" is probably not big enough. I have the 1/2 line and I can still pull the fuel down pretty hard.

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Oh yeah, get rid of the banjo bolts also, if you want to move some fuel. They are very restrictive when you start needing fuel.

[oldschool]

Add a fuel pressure gauge and airdog, raptor or fass. With the comp box and running the stock lift pump, it is just a matter of time before the lift pump can't handle the amount of fuel the comp box is requiring. Next thing to go will be the vp44. Not cheap. Could also be the ball detent valve in the vp44 pump not functioning properly and not allowing the fuel to return to the tank, therefore pressurizing the fuel line back to tank.

Wouldn't that put the tank into a vacuum? and what about the tank vent?

[olred92]

If you ever add bigger sticks or need more fuel, 3/8" is probably not big enough. I have the 1/2 line and I can still pull the fuel down pretty hard.

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Oh yeah, get rid of the banjo bolts also, if you want to move some fuel. They are very restrictive when you start needing fuel.

I was looking at some RV275's for in the future. It wont be to long away though:thumbup2: gotta set the valves soon so it will be then lol. I would like to know which kit Mike got in the article on the Vulcan big line kit that goes all the way back to the tank but cant find it on Vulcan. I just found out that the fuel pressure guage is electrical not mechanical

[Jesnic]

I believe the over flow valve (ball detent) allows anything over 14 psi to go back to the tank and keep fuel flowing to keep the vp44 cool and lubricated. If the ball sticks and the small orifice is clogged, the fuel can't go anywhere and just accumulates in the injection pump and can't cool itself ot lubricate itself. WHen the fuel gets backed up it would create pressure when shut off, if I am thinking right. Kinda like a garden hose when you turn on the water and step on the line to stop flow and then turn the water off, there is still pressure in the line until it is released somehow. Could be wrong though.

[olred92]

I hate to say it but the truck was not treated right before I got it and didnt know that until after I bought it and got it home. Changed oil and filter and fuel filter before i did anything else after I got home and I almost drove 3 hours back to where I bought and hit the guy. I drained the oil and only got a gallon and half or so out of it and when I did the fuel filter I had to wipe the trash out of the bowl with a shop towel. the filter was almost black it was so dirty. the truck has ran great until this and the trans doesnt seem to have any issues. Rear diff cover is leaking a little so that is on the fix it soon list.

[olred92]

The truck started right up this morning. When I got home I did not remove the fuel cap and I will check it again in the morning when I go to Ripley. I believe whatever is happening in the tank whether it is pressure or vacuum is what is causing it to lose prime.

[oldschool]

Vacuum will pull back on prime. Pressure will assist prime. On my truck I have room to reach the module with my hands. Maybe you can inspect the vent.

[olred92]

Ok I have now figured out whether it is pressure or vacuum and it is most definitely vaccum. I stopped to get diesel after I got back from Brownsville, TN and went to pull the cao off and there was enough vacuum on the tank after running for 2-3 hours that I had to PULL the cap off. My big line kit was waiting on me when I got home so I try to get it put on tomorrow and see if that helps. Will check the check the tank vent also and get my guages installed since they are here to.