2nd Gen Non-Engine/Transmission fuel pressure question...

[CEpp]

here's the situation:

when its cold(engine) and start it the fuel pressure is at about 15-16psi (i have a aux pump and factory). but as i drive, with the heat we have been having the fuel pressure increases. more in stop and go where the heat is higher under the hood. ill see 22-28 psi on the guage. its a stewart warner guage with a isolator, fuel to antifreeze. then with the guage reading 22-28psi, i hop back on the freeway and my fuel pressure slowly falls back to 15-16psi.

any ideas? ive taken the gas cap off while running at the high fuel pressure and no difference.

the fuel guage is tapped on the filter housing after the filter.

i have heard of a pressure relief velve on the side of the vp, could that be it?

truck has 130,000miles



want to get it fixed before i head to south carolina for vacation.

 

[Billy Diesel]

Usually fluctuating pressure like that can indicate an LP on the way out. Try discontecting the Aux. pump and see what kind of pressure you get with the stocker.



FWIW, before I put the pusher pump on I had a couple stock LP's go out, and two of them did really odd things with the pressure. The last one would be 8-psi idle, 12-psi just off idle, and then I could pull it down as far as I wanted to when I punched it. It would also bounce around between 5- and 10-psi cruising.

 

[Allnew2Me]

That sounds like the trouble I'm having. I just yesterday connected my Autometer fuel pressure gauge. I took the pressure off the schrader valve at the VP44. I have the Genos hose running to the isolator and then another rubber hose 24" long going to the braided line that runs into the cab. In the morning the gauge reads 0, I start the truck and it rises to 10 psi but rises as underhood temps go up. If I park and leave it for a while, the gauge pegs hard at 15 psi which is the max on my gauge. the problem is that the pressure is only indicated from the isolator to the gauge and doesn't show the actual pressure at the injector pump. So what do i do, get an electrical gauge? I think perhaps the volume of fuel and antifreeze in the hoses may be too sensitive to heat to show any real pressure changes. As long as I look at it when it first starts, i will at least know if there is any pressure, but i am now wondering how accurate this really is and if I would even notice if i lost pressure to the pump, it might just show pressure anyway. I'm not real happy with this setup and would welcome any suggestions. Thanks

 

[LOtero]

very interesting, i have been following fuel pressure threads lately, i just recieved a holley blue and am looking at building a reliable fuel system and this thread is pretty interesting!

 

[RBallard]

I have an electronic setup so I am not completely familiar with your setup but Antifreeze does expand and contract with heat. If you have a small contained volume and add heat you will see a pressure increase. From what your saying that maybe what happens. I know from the past when I was monitoring intake temperatures, with the truck sitting still, the under hood temp goes up and will drop with the truck moving. I'm not saying this is the cause but just something else to consider.

 

[ctopp]

I have a Geno's mechanical fuel gauge set up similar to yours. I was having trouble with bad readings too. In fact I replaced a second LP only to find the new one wasn't registering any pressure either. Turned out to be the isolator was bad. I removed the isolator and ran a hydraulic hose (300 psi rating) direct from filter to gauge. Bought it from a hose shop here in Charlotte and had a union put inline so it can be disconnected. Diesel in the cab isn't the best situation but I can remember guys running gas gauges direct in the old days, so I'm not too worried about diesel. Haven't had any problems and I've been running it close to a year.

Theoretically I don't think temperature should affect the liquid pressure unless you have air in the line. I know it is next to impossible to fill that little antifreeze line completely.

Good luck

ctopp

 

[CEpp]

just replaced the fuel return bypass banjo on the vp-44 and i think its fixed. . stayed around 15 psi and never went any higher than about 17.



u can get it for about 25. 00 @ columbus diesel. (they have a site, just dont know the address) and they stock it.



the are easier to deal with than cummins, who always want a eng. serial #. which i dont keep im my back pocket.



2 thumbs up to those guys. plus they are a rebuild center for the vp and other goodies like injectors and fass.

 

[DieselTweaker]

Chris,



I wish you could have said you needed one, I have a couple in my tool box with new seals.



and the way to shut Bridgeway up is just give them a part number.

 

[DieselMinded]

I have the same set up as you chris minus the overflow thing and I have 12-17 PSI it depends if I fire it up and just take off and never stop it will never past 15psi is I stop and idle it will go to 16-17 and stay while driving . .



DM

 

[Allnew2Me]

I think that when the heat form under the hood increases, the fluid also expands, resulting in a higher reading than actually occurs. So if this is the case, how does a mechanical pressure gauge even show anything close to accurate? It seems that mine is worthless except for the few minutes when I start it up cold. I would rather have a more reliable system. I went with the mechanical because the electronic Autometer setup was blowing out the sender units and Autometer told me they didn't recommend using it with diesels. I think I spent almost as much as i would have for the electric models.

 

[PKleine]

I think that when the heat form under the hood increases, the fluid also expands, resulting in a higher reading than actually occurs. So if this is the case, how does a mechanical pressure gauge even show anything close to accurate? It seems that mine is worthless except for the few minutes when I start it up cold. I would rather have a more reliable system. I went with the mechanical because the electronic Autometer setup was blowing out the sender units and Autometer told me they didn't recommend using it with diesels. I think I spent almost as much as i would have for the electric models.

I was concerned about my mechanical gauges accuracy so I picked up a mechanical test gauge. The test gauge confirmed that my pillar mounted gauge was working properly.



PK

 

[CEpp]

no good... it climbed again today in the 95 deg heat with the a/c on. i drove it last night without the a/c and windows down and really had no probs, but never hit any stop and go traffic. i wonder if the return line is plugged?



one thing to understand, when my trucks fuel pressure is around 22-28 psi, i can shut the truck off and restart and its normal15-16 psi. plugged return line? faulty isolater?

its heat related. . i can tell u that, never had a prob this winter, and if i get on the road doing 55 mph or more, i never see aprob. is whe i get into stop and go and the ambient heat builds in the engine compartment.

im still stumped!

 

[CO Lineman]

I am having the same kind of problem and was wondering if is the lift pump going out and can I count on this thing going out at anytime or putting a load behind my truck put it out of commision sooner... My fuel pressure is good sometimes then it isn't. . Mostly it run around 7-8psi which it used to run arounf 11-12 wot so I am not looking forward to chaninging a lift pump out...

 

[Allnew2Me]

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