Engine/Transmission (1998.5 - 2002) Overlooked fuel delivery consideration and solution??

[24V-DSL]

Hi-jacked this from the DTR, hoping it would generate a lot more discussion over here. I think this makes sense, but if it doesn't, I don't have enough knowledge to say why.



http://www.dieseltruckresource.com/dev/showthread.php?s=&threadid=45276

 

[Gary - K7GLD]

Actually, that has been discussed here several times - as has the notion concerning drawing fuel from a location on the bottom of the tank instead of over the top. Really nothing new - but doesn't hurt to bring it for discussion occasionally for newcomers...

 

[RACE427]

fuel pickup

Someone needs to design a true Diesel pickup with high flow fuel lines for these trucks. What good is converting to 1/2" ID line when you still have a 3/8" ID pickup line in the fuel tank? Less restriction less negative pressure on the lift pump and more volume to the lift pump. The Lift Pump will also have less trouble pulling this negative pressure. Makes sense!

 

[Gary - K7GLD]

The stock fittings and lines on these truck are EASILY capable of supplying all the fuel needed to feed the stock engine and cool the pump - the notion of a "need" for larger line and expensive fittings is vastly overblown, even at higher powers as far as available/needed fuel flow thru the VP-44 is concerned.



The VP-44 at MAXIMUM will pass about 45 GPH - the stock lines and fittings will handle that with no problem - shucks, for THAT matter, as I recall, the stock fuel filter ITSELF will only pass 45 GPH - so what good will larger lines and fittings gonna do unless you change the fuel filter as well? Yer money would be better spent insuring as constant a flow and pressure as possible thru the lines and fittings you already HAVE, rather than concerns about line size...



Then, if you want to "frost the cake", go for those fancy lines and such. The VP-44 will never know the difference...



This subject inevitably stirs substantial controversy - this is MY opinion, and I'm stuck with it!

 

[2broke2smoke]

sorry but i disagree



on my truck a new lift pump gave me 8-13psi ...



only change i made was to a wildcat max flow kit and viola 10-16 psi



this was before any modifications ... approx 20% increase in pressure to the inlet of the vp44 ... with no changes other than removing the stock fuel lines and banjo fittings

 

[Gary - K7GLD]

Doesn't really make much difference, if the VP-44 can only use 45 GPH of the flow, does it! What practical USE is there in the extra 2 or 3 PSI? Actually pretty trivial in view of cost and effort...



You could run fire-hose size water lines to yer yard sprinkler too - but not of much value if the sprinkler head will only pass a 1/8 inch stream...



I get more PSI than that with my setup, lots more filtering, and STILL using all stock lines and fittings... And I'm a bit over "stock" as well...



BUT, to each his own - I'm sure most of us can and will find varying ways to waste our money!



YMMV!

 

[jkern]

gotta agree with gary here... while it is important to have nominally 10psi to the VP-44, it is still all about flow volume. volume does a better job of lubercating and cooling the pump, not pressure.



although that is not to say that you need a pump that is capable to provide 10 psi at open flow volume (read; standing on the smoke pedal, it still needs to provide 10 psi or so)



bottom line is pressure and volume are two different things. what we need is a steady pressure for the variable flow that we have which depends on the fuel use. 10psi or even 20psi won't do us a bit of good at 1 gallon per minute, conversly 100gpm at 2 psi isn't that great either.



i think that if you look at the flow table for 3/8" line you will find that it is more that adquate to provide us the gpm that we need for cooling and fuel supply... the filter is the prime restriction that needs modification.

 

[Gary - K7GLD]

"the filter is the prime restriction that needs modification. "



YUP - and in my case, since I have recently added a pretty restrictive Frantz sub-micronic fuel filter to an ALREADY restrictive system, I might have to re-evaluate MY lines, depending on what surfaces on our RVing trip up along the Oregon coast in a couple of weeks...



Seems to be doing fine empty and around town, but the RV trip will be the acid test...

 

[2broke2smoke]

i read in a previous post that the vp-44 returns fuel to the tank once inlet pressure hits 14 psi ... therefore raising the inlet pressure the additional 3psi would improve cooling of the vp-44 by having a constant flow of fresh fuel, especially considering that cruise with the bigger lines now yields 15-16 psi, as opposed to the 11-12 i had with the stock lines

if the 14psi return theory is incorrect then i'll agree with you guys ...

although i doubt it'll be the last time i waste money

 

[Gary - K7GLD]

AHHHhh - but grasshopper, did you ALSO know there is an INTERNAL, mechanical fuel pump inside the VP-44 to assure proper fuel flow for lubrication and cooling, as long as reasonable pressure is available at the VP-44 inlet?



IF decent GRAVITY fuel flow was assured to the VP-44, we wouldn't even NEED a lift pump...

 

[Sticks]

Well, all I know is that I spent $80 and 3 hours of my time to put on 1/2" fuel lines and move the LP to the frame by the tank, and now my idle pressure is up 3 psi, highway cruising pressure is up 3 psi, and the lowest that I can pull it down is 12, rather than 8 at WOT.



Sure my tank feed and VP44 inlet sizes are the same, but I now have more volume available at the higher pressure for faster recovery.



I am still sticking on my theory that VP44's do not like hot fuel, and installing a small cooler will be the next step, since I know that it is now over fed, and moving lots of fuel back to the tank, thus keeping it lubed and cool.

 

[RHARVEY]

Volume. . volume. . volume!



I did change the lines on my wifes 2k from -6n(3/8") to -8n(1/2") lines. . Not to increase the fuel pressure but the volume that was getting to the VP44 inlet. Did I notice a difference. . yes. . did I increase the fuel pressure. . no.

Last week I added the FASS system to her truck as a replacement for the lp. Did I gain fuel pressure... no, it came preset to 15 psi at idle. Did I gain hp... who knows. . could I tell a difference in how it runs. . yes.

This truck had a push pump back on the frame when we bought it that held 21 psi at idle. Since then I have removed that push pump and ran it with a stock lp with the bigger lines. Even with the stock lp the truck seemed to like 15 psi much better than 21. Now that the FASS system is on. there is a noticeable difference in the truck again.

Fuel pressure at idle has not changed. . but its the volume that is getting to the VP44 and also the quality of the fuel(less or no air in the fuel)



Rick