Engine/Transmission (1998.5 - 2002) L/P and the bottleneck finish filter

[Whitmore]

I believe I have found the bottleneck of our fuel system



First let me explain my system, I have a 60 gallon aux tank in the bed of my truck that is my main feed , I draw right off the bottom of the tank with nothing but a possitive head pressure thru a 1/2" supply line and a 16 micron spin on filter that is rated at 30 GPM, I do know that this is plenty more than addequate flow. My stock pump is mounted just under the filter and has 6an fittings and 1/2" pushlock hose that runs the length of the frame up to the oem finish filter where I have a psi sending unit mounted on the inlet to the filter, then 1/2" hose to the VP-44 with 6an fittings as well and another sending unit at the VP, my gauge on the A piller has a switch so I can read both before and after the filter.



OK this is with a new filter, I have always read 1 psi differential across the filter when new.



Testing the system with comp box on 5x5 and I also have 275 injectors, 5th gear 1800 rpm and punch it the VP reading will go from 12 psi slowly down to about 9psi for say 5 seconds and then psi drops to 0 and stays there till I let up on the loud pedel BUT heres the deal while the VP reads 0 and I switch to read the psi before the filter it will read 11-12 psi, so I now know that the l/p is still supplying pressure to the filter but the filter cannot flow enough to the VP.



I am considering moving the finish filter back to the frame by the pump and if that doesnt work than I want a different higher flow filter in its place. What do you think???



cheers, Kevin

 

[BarryG]

I seem to remember from some long past threads that there is a major restriction within the fuel filter cannister setup I can't remember for sure but maybe it is the fuel heater. I recall some have removed it (whichever part it was) for higher flow. I can't remember if the service manual has a good drawing of the cannister setup or not.

 

[Gary - K7GLD]

I don't have added injectors, but I do have a Comp, and an added Carter pusher pump - the pusher install includes a fuel filter ahead of the pusher between it and the tank.



My fuel pressure at freeway cruise speed holds steady at 20 psi, and under the HEAVIEST towing/grade situations, with the Comp on 5x5, never falls below 18 psi, regardless of how long the grade is - and some here on the west coast are 7% for MILES!



My pressure readings are taken right at the shrader valve at the inlet to the VP-44, the rest of my fuel system, lines, fittings, are all dead stock...



Draw your own conclusions...

 

[Whitmore]

Barry, I do recall seeing a breakdown photo of the fuel heater , this is something I must look into



Gary, here is where you and I differ, I dont want a pusher pump nor do I want 20 psi, maybe its just me but I want to find the restriction so 1 pump will do the job.



cheers, Kevin

 

[tractorface]

Hmm, I have been thinking about switching to a Racor because my guess was that the fuel bowl was too small in our trucks. Have not made up my mind yet because I am not using enough fuel to cause problems yet. Anyone know who makes the OEM unit on our trucks? A slightly larger Racor should be able to be fitted nicely under the hood.



Just thinkin out loud

 

[BV]

I heard Racor designed the the original canister and the first filters for my 99 came labeled with the Racor name.

 

[Gary - K7GLD]

Keven, the only point I was attempting, was the fact that at least on my truck, I see only about a 2-3 psi drop from cruise to full-bore - and while the added injectors will *possibly* add to total fuel flow thru the VP-44 (jury is still out on that one!), I seriously doubt they would ordinarily suck the system down from 12 to to 0 psi - I suspect you have an unusual situation somewhere in your system - possibly in your stock fuel filter, but I doubt your situation is typical... Forget about the pusher part - focus on the PSI difference between cruise and full-demand...



Put another way, a lot of guys here are running similar setups to yours in terms of power add-ons - and have guages installed after the fuel filter - I don't see any of them reporting 0 psi at full demand...



But then, maybe I missed something somewhere...

 

[Whitmore]

Well the curiosity on the fuel heater got to me so I removed it totally and tried it again and it is still the same results



I am at a quandry here and feal I am pi$$ing in the wind



Gary, I understand what you are saying but the 2 comparisons are apples and oranges, I still aint want no pusher pump ifin I can gets away frum it :{



cheers, Kevin

 

[15w40]

Something just doesn’t add up. The VP-44 will flow 30 gph back to the tank at maximum rpm. The stock fuel filter is reported to flow 45 gph at some unknown (?) pressure drop. If the filter you added between the bed mounted tank and the lift pump only flows 30 gph, how can the pre filter reading stay up at 11 - 12 psi? I would think that it would drop off also.



I wonder if you swapped the two pressure senders if you would see the same results?

 

[Whitmore]

Dave,

My pre filter flows 30 GPM not GPH, I do know that this filter is not the problem because I have the 2 senders before and after my finish filter and yes I did trade places with the 2 senders and it made no difference, I am very confused at this point and just dont know what to do. When I removed the fuel heater from the finish filter I looked the housing over real good and I cant see a restriction anywhere, I had this problem with my OEM lines and thats what prompted me to take the plunge on the new larger lines.



thanks, Kevin

 

[Ncostello]

Our fellow member Kyle has already done a nice installation of a Raycor 90 GPH 2 micron filter and filter head. His photos are available in Readers Rigs... KYLE. It looks great and works great according to him. He simply removed the stock filter unit and replaced with the Raycor model. It looks like Cummins put it there.

 

[15w40]

Doh! 30 gpm not 30 gph. Maybe I should see my eye doc.



That is a mystery. The only way the pressure could drop is by a restriction in flow. I would be surprised if the factory fuel filter is that restrictive with the enhancements you have added. Have you checked the hose you added between the filter and VP-44 for obstruction? I?m running out of ideas.

''

 

[Whitmore]

Dave,

I had this problem with my oem lines, the only mods I had were high flow banjo bolts, thats why I went to the new lines with higher flow yet and the dern problem is still there and I may add to that this is a new L/P as well so the only thing that is being used now that was part of the original setup is the finish filter



Kevin

 

[Big White Beast]

Kevin........

After reading this thread I seem to think this is a problem that is exclusive to your truck. Here's my 2¢ worth,



When you swapped senders did you do completely swap out hoses (Assuming their remoted up top). Try a mechanical gauge hooked up temporarily to see if this is a true reading.



Seeings you have adequate filtration on your rear filter I would bypass temporarily the stock filter housing. If this eliminates the problem one would have to assume your factory housing was defective. A short jumper hose or coupler if your lines have some slack would be an easy check.



This would either confirm or eliminate the factory housing as the problem.



Garrett

 

[Whitmore]

Good tip Garrett, I was thinking the same thing, when I get time I will do a remote mechanical gauge to the windshield to confirm the psi, If still bad I will also try to bypass the first filter as a process of elimination just to clear my mind.



cheers, Kevin

 

[Big White Beast]

Curiosity is peaked.......

Be sure to let us know what you find out.



Garrett

 

[15w40]

Be careful on eliminating that factory fuel filter. You run the risk of particles from the carbon, lift pump brushes trashing the VP-44.



Maybe if you disconnect the fuel line at the VP-44 and use it to fill a bucket while monitoring the pressure gauge, bump the starter, it might tell you something. If the pressure, pre-filter is still at 11 psi then it has to be the filter or banjos. Maybe time for some AN-6 fittings or as the Raycor 90 filter although several people run the stock filter, modified banjos, and the stock pump with good results.

 

[Gary - K7GLD]

"Be careful on eliminating that factory fuel filter. You run the risk of particles from the carbon, lift pump brushes trashing the VP-44. "



Excuse me - but are you suggesting that the *LP MOTOR* is running in the fuel stream? If so,



BZZZZT! *WRONG*!



The electric motor spinning the fuel pump vanes is in a completely DIFFERENT, separate housing and totally isolated from the fuel pumping section...



"although several people run the stock filter, modified banjos, and the stock pump with good results. "



MOST fellas run similar power enhancers with the stock lines, fittings and fuel filter with no problems - that's what makes this case so puzzling...

 

[Snow man]

Whitmore I got to tell you. I run the Bully Dog 7's,with the drag comp and basically a stock fuel system with a fresh lift pump,and a carter pusher pump. I use the rays banjo bolts,and drilled the 2 restrictive banjo's. I have no an fittings or special anything. I couldnt get my FP below 5-7psi WOT at the vp44 inlet. I have 18-24 psi at idle. Maybe something is restrictive in your filter housing or you got a restrictive stock filter. I will replace everything in my system as soon as I reach its limits. I cant see replacing whats working fine.

 

[Whitmore]

I better clarify that when I said I would bypass my first filter that that is the filter before the L/P and yes I do know how important the final filter is to get it clean as a whistle before use in the VP-44, I would never be without filtration there.



Gary you need to know that the L/P is a wet sump, it does have fuel in the electric motor drive, you are correct that it is a seperate chamber than the pump BUT the spillback circulates thru the motor drive for cooling, thats right the little spring and ball afair when it opens up the fuel circs thru the drive motor and back to the suction side of the pump, this is so the pump does not deadhead and for cooling as well.



I did get a mechanical gauge today but didnt have time to mess with it , darn night shifts yaknow a guy has to sleep sometimes.



cheers, Kevin