Engine/Transmission (1998.5 - 2002) VP 44 and fuel system gurus need advice

[BarryG]

I have an 01 which has the vp44. I have put in a cam and have switched to a 12 valve mechanical fuel transfer pump. I have put in a bypass to deal with the excess pressure. My problem started before the pump conversion and does it with or without the bypass plumbed in. The pump will make upper 30's psi without the bypass. However it does this with or without the bypass installed and again it did this before the pump conversion. I have replaced the line from the fuel filter cannister to the vp long ago. I have plumbed in a second fuel pressure gauge temporarily to verify the guage works correctly and they both mirror each other pretty closely one is pre filter the other is post filter. I have replaced the fuel tank cannister with a liberty module with the draw straw installed. I have replaced the lines from the tank to the hardline along the frame. So on the supply side the only stock thing left is the hardline along the frame rail and the fuel filter cannister. The return side is pretty much stock except for the hardline to the tank. It has also done this with more than one VP 44. Also there are no apparent leaks. It always starts just fine no cranking just fires right up.



Now to what happens is that I will lose fuel pressure. It will drop from my normal 16-17psi to 10, 5, or even 2psi. It only does it randomly sometimes more often than others. Sometimes it lasts a while other times it does not. Many times if driving down the road and it drops to say 5 if I slide it into neutral and rev the engine a couple times it will come back fine until the next time which may be that day or next week.



I am at a loss as to what is up. When it does it the truck does not act like it is starving for fuel seems to run fine even with a trailer going up a mountain pass at 30psi of boost. Can the VP 44 free flow fuel through the return line? I have replaced the check valve at the outlet of the vp on the return line. Am unsure of if that valve also acts as a bypass for the vp, but in any case it has been replaced.



Looking for advice on where to check it is driving me nuts.

 

[jandtjil]

I am guessing that each gauge has a separate isolator? Which odds are both are not having issues... .
Did you say you have a separate bypass, not including the VP check valve? If so does the 2nd bypass feed into the VP tank return line (small diam steel line)?

JJ

 

[BarryG]

With gauges reading pretty close to each and one prefilter and the other post I would expect a little difference. I do have another bypass in addition to the VP's bypass. The bypass is prefilter and returns to the tank canister setup via its own line. My canister is the modified Jeep Liberty module and has an additional fitting for a second return line as part of the modification along with the drawstraw.

DrawStraw™ V HiFlow



I used the liberty module setup in the hopes of fixing this issue as my original canister had a torn screen (and the liberty module was 1/2 the price of new stock one) and I thought perhaps the suction was pulling the flap of screen up and blocking the suction tube but alas that was not the case.

 

[jandtjil]

When you swapped out previous VPs or (vp) check valves did the issue clear up, or was it a problem at the time?

 

[BarryG]

After the VP was replaced it still did it. I went ahead and replaced the check valve late last year and it still does it.



What I cant tell and would love to know is whether it is really starving for fuel which you cant tell by the way it runs or if it is somehow freeflowing through the VP and out the return line which seems unlikely as it has done it on two different VPs.



On a side note when I was first really trying to get this fixed and putting in the temp gauge, checking the bypass etc it was doing it really bad as in much more frequent. It would slowly drop to 2psi and would be that at shutdown of the engine. Then after I would open up the fuel system to plumb in the gauge or take out or reinstall the bypass or whatever I might be checking it would be great at startup and within a few miles of driving it would be back down to 2 psi. Open up the system again and it would be good again. If I just shut it down and didnt open the system it would startup with low pressure. Which made me think maybe there was some sort of vacumn issue with the vent or something. So I tried running with the fuel cap loose and even off to eliminate that possiblility and it still did it so I determined it is not a vacumn in the tank. Original rollover/vent valve in the tank seem to test ok as well.



Appreciate the brainpower you are putting towards my issue.

 

[jandtjil]

Kink in the fuel line leaving the drawstraw?
Since it is showing consistent PSI both pre/post filter, consider checking your return/bypass at the filter again.
jj

 

[DFerverda]

When i had my walbro pump on the truck, with their bypass it worked fine. After the second or third pump, i went to a Raptor 100 and had all kinds of weird pressure issues until i removed the bypass.
I think the post filter bypass was opening at the right pressure and the vp bypass was also correct but sometimes the pump may have been caught in limbo, ie caught in the middle .
After removing the extra bypass it went away.
Something to look at.
Dirk

 

[Sticks]

Are you getting any air in the system?

Another possibility is that you have a floater in the tank that is clogging up the strainer sock on your fuel sending unit. Might try to plumb in a vacuum gauge pre transfer pump and see if the vacuum gets higher as the pressure drops.

 

[BarryG]

DF:

I have the stock vp44 bypass which I cant remove and I have a seperate bypass prefilter that is plumbed back to the fuel tank canister. If I remove that it still does it and the pump can make 40psi without the bypass. However the truck runs fine. Just a bit leary of taking the bypass out for longer than testing purposes though the guy at Vulcan Performance tells me he runs his VP truck with 40 psi for years with no problems not even hard starting.



Sticks:

Air in the system is a possibility however I cant for the life me find where it would be coming from. I can find no leaks or even weeps, it runs fine even at its worst low pressure(1-2psi) it still seems to run fine even pulling a trailer up Eisenhower. As far as a floater the inside of the tank is clean as a whistle. I did have a tear in the screen of the tank module and thought maybe it was sucking that up and impeding flow so I replaced the whole module with a modified liberty module that has the drawstraw installed and doesnt use a fabric type screen, it still does it. I have tried running it with the fuel cap off to eliminate a vacumn situation with a poor vent but no cap it will still do it.

 

[Sticks]

Good lord, it was not until you said Eisenhower that I realized who you were. How ya been Barry?



Broken stand pipe was the source of air I was thinking, but you may have eliminated that by replacing the module... However, I have seen the quick connect fittings suck air but not leak a drop of fuel when the tank was pressurized up to 15psi and held for 1/2 an hour. The one by the OEM LP mounting was the worst one for this.



On the OEM fuel system, the only pressure relief valve/check valve was at the VP. Everything else is open flow.



If I had it in a shop;



1. Blow out all your fuel lines to remove any possible obstructions that are caught in the middle.



2. I'd be eliminating the fuel tank and lines and plumbing in a separate fuel supply directly to your pump and see what that does. nfortunately you have this random problem that you can not duplicate on demand. I can't remember if you have an in bed reserve tank or not.



I have a 30 or 40 gallon fuel tank off a generator that you could borrow. Been sitting in my garage for the last 4 years staring at me. You could strap that down in your bed and try that for a week or three. I can not vouch for the cleanliness of the tank (had no cover for the fuel level sending unit when I got it). I did a cleaning on it when I first got it and used it a couple of times with no issue, but another good rinsing and drying wouldn't hurt, and should take care of the worst of what may be in there and your filter would catch the rest.



Since you had this problem before you made the LP conversion, and have since replaced the VP and the return valve, your problem most likely resides in what is still there from the beginning. Banjo bolts, fuel lines, filter housing...

 

[BarryG]

Yeah Sticks its me and just busy busy but all is well. Good to see you back on the forums lately had wondered for a while if you had fallen off the face of the planet.



The new tank module does not use the dorman quick connect fittings. And since they werent needed there I cut them off where the tank lines attach to the hardline at the frame as well and double band clamped them there. The only stock fuel system parts left on the truck up to the VP is the tank itself which is clean, the hardlines along the frame rail and the filter canister. And since I have a gauge post filter and temp gauge prefilter (is it still a temp gauge when it is there for 9 months) and they mirror each other I dont think it is a leak in the canister as I would see that due to it would have to be a serious leak nor do I think an obstruction in the canister as then the prefilter gauge would still read good pressure and just bypass the fuel back to the tank. The banjos are long gone and replaced with aeroquip type fittings.



I am beginning to think there is some sort of odd obstruction in the fuel line between the tank and the pump. Even though my logic tells me that an obstruction in the line would be there or it wouldnt, not be random. I think my next step is to replace the fuel line from the tank to the pump and bypass the hardline in the process.



Keep the ideas coming and thanks for the input.

 

[Sticks]

Try blowing out the hard line along the frame and see what happens. You might have a chunk in there that is getting hung up at a bend in the line, and when you shut down/relieve suction, it frees up and tumbles back down the line, or worse yet, a flake that is kind of hinged inside the line, like a flapper valve... you have not been running any chicken fat have you?

I'd still like to see what a vacuum gauge reads pre lift pump.

 

[BarryG]

I will try blowing it out. I am sort of thinking the same thing with your flapper valve analogy it is about the only explanation left. No, no chicken fat or any other type of waste oil or veggie oil for that matter.



As far as vacumn gauge I dont have a real one however my spa fuel pressure gauge will read vacumn maybe I can just plumb it in prefilter and see what happens. Where would you suggest I place it, back by the tank or just anywhere pre pump? And what reading should I look for? Since it will be under suction there should be some vacumn right?



Just need to find the time.

 

[Sticks]

Not sure what type of reading you will get, as I have never done this on a Dodge (not even sure if they have a spec on it). I would venture to guess that normal vacuum should be somewhere around 3" - 8". 15" or more would indicate a problem to me.

Right in front of the pump would work. As your pressure side drops, if you have a restriction in fuel supply system, your vacuum should go up. If it does not, your problem lies after the pump somewhere on the pressure side.

I know, time to do stuff is in short supply. Might be faster to go ahead and just upgrade your fuel supply line to 3/8" or 1/2" and see what happens.

 

[Sticks]

Any luck with your problem?

 

[BarryG]

Well Sticks I got around to it last night.

I was changing my right rear caliper and then tore into dropping the tank. Of course it started to rain as soon as I got it down. So I didnt take the time I would have liked to on this project. I just cut my old line off at the tank fitting and swapped in the new line. Fed it up to the pump tore off the old line there for a complete replacement from tank to pump. In fact now that I think abvout it I think I still have a pair of vice grips pinching off the old line at the tank hanging on the frame rail oops better get that. In any case due to the rain I did not test or blow out the hardline or even remove it. Just ran new line. Truck started up and pressure was steady at 15-16psi like it should be. Previously it would swing more than one would expect.



However while I was dropping the tank found another boo boo. My freaking center support bearing for the driveshaft is toast. The rubber part is all torn up so my driveshaft is a bit loose. So I really just drove around the block gingerly to test my brakes and watched my pressure. It was steady which is an improvement. To early to tell if it is fixed due to the driveshaft deal.



Did you deal much with the center carrier bearing up there at Central Motive? If so what was the best option. My original one lasted over 200k. Then when replaced it lasted about 100 miles, replaced for free that one lasted 100 miles. Got fed up with that and took it to a real driveshaft shop and that one lasted about 10k. Getting tired of this garbage. Any insight would be appreciated.

 

[Sticks]

I have only done one carrier bearing on a Dodge, and that was a TDR member back in '04 (I think) in my garage. Can't remember where he got it, or how long it lasted (lost touch). If the OEM lasted 200k, may as well get another one from ... the stealership ... gods help you.

 

[Sticks]

Now that I have slept on the matter, I wonder if your drive shaft is tweaked a bit if you are going through carrier bearings. Might want to have it checked for clocking, balance and straightness... and that is a whole 'nother thread.

Keep us up to date on the fuel system. This one was perplexing.

 

[BarryG]

Well put the driveshaft back in last night and drove the truck to work this morning. Good news is I didnt screw up the driveshaft r&r seems to work with no problems. Bad news is replacing the fuel line from tank to pump did not fix my pressure issue.



So Sticks put your thinking cap back on. To summarize it has done this with more than one pump. My current pump is a mechancial pump from a 12 valve (installed a cam with a pump lobe) and it will put out approx 40psi with no bypass. I have the bypass set at approx 16psi. It will do this with the bypass in or out. So it is not the pump or the bypass. I have replaced the line from the tank to the pump so it is not a blockage in that. I have replaced the tank module so I seriously doubt that it is the pickup tube which is a drawstraw in the modified Jeep Liberty module. I have a gauge pre and post filter they both read pretty close to each other so again I doubt it is a funky guage (one is electric one is mechanical). If it was a blockage in the stock filter setup I would expect to see post filter gauge reading low and the prefilter gauge reading high/normal just bypassing the fuel. If it was a blockage past my gauges I would expect both to read normal and again just return the fuel via the bypass. There are no leaks or weeps that I can find and certainly nothing to indicate a leak of the magnitude it would require to drop from 40psi to 2psi (when I have tested it without the bypass). I think I have eliminated a possible vacum in the tank issue as it will do this with the fuel cap on or off. At one time I thought perhaps it was free flowing through the VP44 but it has done this on more than one VP. So I am having trouble believing it is that or how that is even possible, maybe bad overflow valve or whatever it is called on the return line at the VP but I have replaced it as well. What the heck is left? I am completely stumped. By the way the truck starts fine and runs fine even with a trailer in the mountains. It doesnt seem to be starving for fuel when acting up.



Fuel pressure will swing erratically and sometimes be very low. If driving I can shift into neutral and rev it up high and that will usually fix the low pressure but not necessarily the erratic pressure. One thing I have noticed during all of my testing this or that is that if the pressure is low at shutoff and I do nothing at startup it is still low. However if I open up the system say to replace the fuel line in the latest example it will read good and steady for a while then it goes back to its erratic behavior. I was really bummed at halfway to work this morning when it started doing it again.

 

[Sticks]

Pondering...