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

[Gary - K7GLD]

"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 separate 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. "



IF so, that is certainly news to me - and my apologies to the fella above - YUK - Crow in the morning sure do taste BAD...



(EDIT)



The more I think about the above, the more puzzled I get - IF the fuel bypass DOES circulate thruout the drive motor, including the brush area - how is an explosion avoided with highly flammable fuels with the sparking common to brushes in DC motors? I realize oxygen is needed to support combustion, but it seems to me that cavitation and other natural events would frequently add air bubble's to the fuel mix, and then BOOM!



As far as I know, these same pump types are used with other fuels besides the less explosive diesel...

 

[apkole]

Wow, timely subject. It was about 8 below here this morning. Plugged the truck in for a couple of hours before heading out. Got a couple of miles down the road. Noticed that under moderate acceleration could get the fp down to about 5. I'm using an antigel additive consistently on every fill. I haven't noticed low fp until this morning.



Have had a busy week of plowing snow, so left truck plugged in when not in use to keep things warm and ready to go. Perhaps short plug in period this am aggravated the cold fuel situation?



Andy

 

[Whitmore]

OK hears the deal Guys

I made time to give it a look, I am now bypassing the filter between the fueltank and the L/P, its gravity fead from the aux tank right into the suction of the L/P and I gained a pound extra all the way around, I have 15 at idle and cruzing at 70 I have 13psi, at WOT with no comp on I can go from 65 to 115 and it will only go down to 12 psi, with comp on 1x1 same deal only 11 psi now with comp on 5x5 from 65 to 115 I can pull it down to 10 psi, this is great pressure BUT around 100 mph the psi will drop to 0 and stay there till I back off the throttle



Hear is where I am confussed, my numbers soud better than any I have read hear for the stock l/p but what is up with the damn thing dropping to 0 psi at 100mph :confused



Hopefull tomorrow I will be able to hookup the mechanical gauge to confirm my numbers.



cheers, Kevin

 

[Big White Beast]

OK here a thought..........

You obviously have the wire hooked to the VP. I'm curious if the engine governor is somehow trying to shut down the fuel and the comp is overriding it. Or something like that. How is the relocated lift pump wired? Did you just extend the existing wiring? Does the ECM idle the lift pump when defueling?



I know there are plenty on the TDR that go that fast and don't seem to have problems. I'm just guessing and hoping that those more informed on governors/defueling will chime in.



Now is this the same scenario, Pre stock filter the pressure is OK and Post it's not?



Garrett

 

[Gary - K7GLD]

I wonder if it's LOAD related, or purely an engine RPM thing?



Can you drop a gear to reduce road speed/load, and then wind it to the same RPM and still see the same psi drop? Maybe the internal VP-44 LP outpacing the external one at higher RPMs?

 

[BillGotthelf]

Heres what I have-Fresh LP, fresh Inj pump-Stock fuel filter, bigger banjos-tst pmax3, DDIII's, Piers HX40, ATS exhaust manifold. At idle-15/14. 5 60mph-13-12. 5 WOT-7. 5/7 . It sounds like the electrical signal to the LP is being reduced. Could the computer be getting crossed signals about pressure and cycling back as it is supposed to do at idle to prevent over pressure to lift pump?

 

[Gary - K7GLD]

I questioned Edge about comments I have read about the Comp "defueling" at/above 2700 RPM - they claimed the defueling was due to the ECM, NOT their Comp, altho' they also said their Drag Comp (I think it was) circumvented that characteristic.



I had assumed the "defueling" was accomplished by fuel management between the ECM and VP-44 - but now wonder if it might be done by reducing voltage to the LP?



Still, this doesn't seem to be a common problem, as you would think it would be if it was designed into the ECM...

 

[Whitmore]

This is a freash L/P and I also got the pigtail 10" wire extention so I could extend the wiring to the rear of the truck, I know I have it wired right as the wires were coded #1 and #2 and I was very cautious to make that right. anyhow if I do this same test in 5th gear it will do the same thing... ... ... ... ... ... hold around 10-11psi thru the acceleration and when you about wind out the psi will just drop like a rock to 0 psi, so I dont think its a de-fueling thing as I wasnt wound tight yet on rpm's. Oh and thru all this the psi at the prefilter is still at 10-11 psi.



Another reason I know its not a de-fueling issue from the ecm is because earlier in this problem when I was using the filter between the tank and the pump it would do the same thing other than alot earlier and alot less rpm and mph.



Once again the thing I am impressed with the most is thru acceleration the L/P will hold at 10-11 psi @ WOT to the VP and that is great. I do believe that this proves the new fuel lines are alot better setup than the OEM units. Keep in mind that the reason I upgraded the lines was because MY stock setup would not hold any psi at the L/P with no bombs, I changed to a fresh L/P and it wasnt alot better but some and then I added the new lines and it was 90% better, I think I am on the edge of figgerin this thing out though.



Cheers, Kevin

 

[Roger rodbolt]

Just a couple of thoughts on fuel systems, I played with them for a while. You definately need a fuel filter after a Carter lift pump to catch the debris as it wears out . If you are having difficulty with fuel/fuel pressure while running stock or small (275hp) injectors with dual pumps, something is wrong with your system. You can't push much fuel through those tiny injectors... ... ... ... ... ... ... ..... Larry

 

[Gary - K7GLD]

One final thought, then I'm about dry of ideas - wonder if you might have a bad fuel bypass valve inside the VP-44 that is causing WAY too much fuel to be internally bypassing the VP-44, and returned to the tank - that WOULD seem to get progressively more severe at higher RPM, as the VP-44 internal mechanical LP increases in speed with engine RPM...

 

[15w40]

Since we are all scratching our heads on this, or at least I am, how about a WAG. Is it possible that at high engine RPM the flow through the fuel system is at a maximum? If the fuel pressure gauge attached to the VP-44 is creating a venturi effect the pressure could fall to zero or even negative. This would always happen at the same high RPM.

 

[Whitmore]

OK hers the deal, I hooked up a mechanical gauge at the VP-44 and gave it a test run only to find out that the my original readings from the electrical sender were correct, at WOT with comp on 5x5 psi would come down to 10-11 psi and hold till 100 mph and drop down to 0psi, then I tried the same thing in 5th gear and sure enough at 3k rpm the gauge would drop to 0 again, I just dont get it



How about this, could I have a leak in one of my injector connecting tubes that is letting all my fuel return to the tank via the return gallery, I have been thinking that I should disconnect my return hose and put it going into a clear bucket ontop of my toolbox in the back so I can see it, then I would know if there is any return fuel when the thing goes to 0psi or if the motor is using all the fuel



cheers, Kevin

 

[Gary - K7GLD]

Kevin re-read what I posted above about the possibility of a bad fuel return valve INSIDE the VP-44...



At low RPM, the restriction of the VP-44 internal mechanical lift pump would still hold inlet PSI high - but as engine speed increases, the internal VP-44 LP *might* be outrunning the ability of the stock EXTERNAL pump to keep up - and then allowing a high percentage of fuel to bypass the VP-44 and dump back to the fuel tank, and resulting in zero psi at the inlet to the VP-44 at high RPM.



The VP-44 bypass valve is SUPPOSED to open at around 14 psi, regardless of engine RPM - but if that valve has failed...

 

[RADdodge]

Whitmore, is this a trick question?



I would agree with Gary EXCEPT that you see 11-12 psi before the OEM filter. If the by-pass valve were the culprit (or just the VP44 taking all the fuel available for whatever reason), you would also see the pressure before the OEM filter at about 1 psi or whatever the differential is which is generally only a few psi at most (6 in/hg max).



Even if you look at it in GPH, the VP44 is getting just barely what it needs after the filter according to your gage reading of 0 psi, but a surplus of fuel before the filter with 12 psi! Unless Dave (15w40) is guessing correctly with a venturi effect, I would look a lot harder at the OEM filter canister and the line from it to the VP44.



This is a good one; sorry you have to suffer from the plague of not knowing the cause. That would bug me to no end. As it is, it still bugs me.



You said that this was the reason you upgraded the fuel lines to begin with? Was it just the same or a little different? If it is a venturi effect, you might fix it or at least change where it occurs by reducing the size of the line between the OEM fuel filter canister and the VP44. Try your original line if all else fails. If it were me, I’d find another filter to try, not just the filter element, the whole thing, canister and all.



Oh, one question left, where exactly is the second FP sender unit (where did you connect the mechanical gage too)? Is it between or in the line from the OEM filter canister to the VP44?

 

[Whitmore]

FP mechanical gauge is hooked up to an -6an male -6an female fiting at the inlet to the VP and has a 1/8" npt tap on the side where I ran the line from and the other fp measurment is an electrical sender at the inlet to the OEM filter , I have a brand new filter in it too and the fuel heater is pulled out as well, pulling the heater seamed to make no difference at all.

I said the reason I upgraded my lines and a fresh pump is because of this very problem , only diff is with the old lines and pump I was at 5 psi WOT when it would fall to 0psi and this was with the comp off so the only enhancment was 275 injectors.

I like your idea of a new filter canister and all and have considered it but would like to know how many micron filtration is needed and would also like to know what gph flow is required so I can get a higher flow model, If I could find a better filter and housing I would like to mount it on the frame rail just downstream of the pump, that would free up some room under the hood and I dont mind crawling under the truck so no biggie here.



cheers, Kevin

 

[JWhitcomb]

Just wondering when a pump becomes a pusher pump. Wouldn't a stock lift mounted away from the engine and getting gravity feed be considered a pusher. If it pushed to a stock pump mounted in the factory position would it then be a pusher pump? Just thinking out loud here, not trying to start anything.

 

[Whitmore]

In my book a pusher is a pump that feeds another pump so in my case I dont look at my setup as being a pusher, yes it is pushing or pumping the fuel instead of sucking the fuel or having a vacumn, I do know that no pump likes a vacumn and all pumps enjoy a positive head pressure , thats the reason I opted to give my pump a positive head, I do believe that the pump is happier now and not having to strain by lifting fuel but just pumping instead. I know one thing for sure when I filled my auxillary inbed tank up with fuel and started to hook up the supply I decided to put a gauge on it as it sat and the static pressure was almost a pound just from the head pressure alone, this tells me alot about load factor on the pump and how well and how long it will be able to do its job sucessfully. I have the opinion that the current Carter L/P is of good quality and is a reliable under proper conditions, I believe that the OEM setup that DC carelessly put together is not condusive nor healthy to the L/p and that is why we are having so much trouble with pump failure. I really want to get my problem in order and then sit back and see how long and how well this OEM L/P is going to do for the application. I am possitive that the problem I am currently experiencing is not related to the feed to the lift and I KNOW that my problem would be alot worse if I were still in the vacumn status vs. positive pressure. There is another TDR member that has installed a tap on the bottom of his OEM tank to feed the lift and his reliability has been great so far too.



Rock on, Kevin

 

[Gary - K7GLD]

Kevin, if you're unable to locate a substitute filter for testing purposes, and don't want to spend the price for one purely for speculation, why not temporarily buy a decent cheaper substitute just for a short test, and totally bypass the stock filter? It would only be for a short test - perhaps you could use the same type used ahead of your existing pump, and when the test is over, keep it as a spare?



Or for that matter, and for simply a few minutes test, be scrupulously careful and clean, and just temporarily bypass the filter with a hose...



Have you had the stock filter housing off the engine? Have you tried removing the filter element, then applying air pressure to check for flow? - yeah, that's sorta hard to interpret and properly compare to fluid flow, but might reveal a serious restriction... A poor casting or machining flaw MIGHT be internally restricting flow somewhere out of visual range...



For that matter, is it possible to re-drill entrance and exit ports on these housings for increased fuel flow, as we do with the fittings?

 

[RADdodge]

It Has to be the Filter...

Whitmore – I can’t see where any of your methodology could be faulted. I think you took everything to the next practical step. The only thing I can think of is that you have a defective filter (I know it’s a new filter element, maybe just try another).



I was looking at the Racor filter catalog and I ran across this for estimating filter flow:



Diesel or kerosene fuel systems:

Gallons per Hour is Engine Horsepower (maximum) multiplied by 18% or GPH = HP X 0. 18



Using that figure, 225hp would be 40 gph, 500hp would be 90gph and 350hp translates to 63gph. I think our OEM filter is rated at 45gph. I don’t know what your rated HP is, but it may be more than the OEM filer can pass when you are hitting peak horsepower. I believe the Cummins peak HP is at about 2600 RPM. The symptoms of such a situation would seem to match what you are seeing. Flows ok when under peak hp, but chokes off at peak hp and highest flow demands. You would need to find a higher flowing filter to know for sure. Maybe there is a higher flowing filter that would fit the OEM canister. That would be the least expensive route. Or knowing that 0 psi is going to happen at extremes. But some how I don’t think you’re going to settle for THAT!!!



If your were looking to replace the complete filter set-up, I would recommend a Racor filter. I use one ahead of my pusher pump and it has worked very well. But I don’t think you should have to go to the expense of that to figure this one out. I would recommend a Racor though. The reasons are: 1) There are a variety of spin-on filters available from 2 to 30 microns available with flow rates from 45 to 90 gph (the more gph, the taller the filter). They can be had with WIF sensor and heaters. I have a PDF catalog that shows the options and various filters. I can email it to you if you’re interested or it’s available on their site.

 

[Gary - K7GLD]

"I think our OEM filter is rated at 45gph. "



But at what PSI?



Flow rate, to a point, WILL vary according to applied fuel pressure...