Engine/Transmission (1998.5 - 2002) What is the fuel flow in a 3/8" line?

[Gary - K7GLD]

Pressure is one of MY main concerns with my own system - too MUCH pressure!



I run 25 psi at idle, 21 at cruise, regardless of load, and never less than 18 psi at WOT - right at the inlet to the VP44... I have 2 concerns, potential internal problems to the VP44 at the elevated PSI, and the potential for on-the-road problems if my added pump fails for any reason, creating a serious fuel flow obstruction that would shut down flow, and the engine. The 4600 will NOT allow fuel flow if its not running, period - so a dead one is like a big plug in the fuel line!



Not a GOOD thing along some lonely deserted stretch of road with a trailer in tow...



That's the reason for my new second "experimental" 4600 pusher - I working up a bypass/flow valve that will bleed off a small amount of flow from output to input of the 4600 to slightly reduce pressure, and if the 4600 fails, the one-way valve will allow at least enough fuel flow to maintain reasonable fuel flow and engine operation until proper repairs can be made. It turned out to be a simple manifold-type arrangement made up of about $15 worth of commonly available 3/8 inch pipe fittings...



I already have it all ready for installation, just want to take some detailed pictures of what's involved, and find time to get it done - wish me luck!

 

[Diesel Freak]

GRRRRRRRRRRRRRRRRRRRRRRRR!



The comment that installing larger injectors lowers fuel pressure is absolutely FALSE!



The only thing that will lower fuel pressure is installing a fueling box!



Injectors DO NOT CHANGE VP44 DUTY CYCLE!





On a lighter note, what is the bypass on the stock lift pump set to lift at?



I had some weird things happen this weekend when the temp dropped into the 20's



when turning the key to "on" and the lift pump cycled, the Indications I had could only be that of the VP44 bypass Relief lifting.





This is what happened. The lift pump cycled. Pressure built to over 15psi, and then dropped to 12 psi at the same time the lift pump audibly increased in RPM from the drop in discharge pressure. I can only assume that the VP44 bypass lifted off and blew down to 12 PSI.



This has never happened when the temp was over 40F.



With the engine running fuel pressure is at 14 psi.



Just something to note.

 

[J.R. Adkins]

DF- so explain droping the FP with no box AND HUGE injectors only!

 

[Diesel Freak]

Originally posted by J. R. Adkins

DF- so explain droping the FP with no box AND HUGE injectors only!

I have not seen any difference from stock injectors, 275's and DD3's



The VP44 is a positive displacement Pump.



Injectors do not affect the ammount of fuel that flows through the VP44. They do not affect VP44 duty cycle.



Injectors just divert more of the available fuel from the VP44 into the combustion chamber.



Injectors do not raise overall fuel flow into and out of the VP44.



Fuel flows to to three different places after it enters the VP44



1. it is bypassed back to the fuel tank



2. it is pumped to the fuel injector where it is injected into the combustion chamber



3. it is pumped to the fuel injector where it gets diverted to the fuel recovery galley and flows back to the fuel tank.



Injectors just inject more of the available fuel to the combustion chamber and divert less back to the fuel tank.

 

[J.R. Adkins]

All of those injectors that you listed are small. I seen a set that are larger than BD8's pull the fp down at WOT to 0 VS. WOT with dd3's and 12 PSI FP.





J. R.

 

[Diesel Freak]

Hmmm that is quite odd. Something does not add up. Unless you are running over 3500 RPM.

 

[J.R. Adkins]

Nope its a 24v.

 

[Jetpilot]

I have to agree with J. R. here. I have seen large injectors make a huge difference in the fuel pressure. Including pulling it down to 0. In fact I think that we have found the limit on fuel that the VP44 will deliver. I have gone to larger and larger injectors but now I don't seem to be able to make any more HP even with more N02 and larger injectors... ...



Doug

 

[Diesel Freak]

well, dont take this personally, but I have to throw a flag on this one. With a Stock VP44 and nothing but a Boost module as electronic Mods. Regardless of Injector size there is no physical reason for fuel pressure to change at WOT.



I have a question.....



What happens to the flow rate and discharge pressure of a positive displacement pump when you raise and lower a restriction on its outlet?

 

[J.R. Adkins]

DF



Just to let you know we made 480 HP on injectors and a Van Aken only. With a single Piers 40.







J. R.

 

[Diesel Freak]

Originally posted by J. R. Adkins

DF



Just to let you know we made 480 HP on injectors and a Van Aken only. With a single Piers 40.







J. R.

cool, but... ... .....

 

[Whitmore]

F/P #'s

Originally posted by Diesel Freak

GRRRRRRRRRRRRRRRRRRRRRRRR!

















On a lighter note, what is the bypass on the stock lift pump set to lift at?



I had some weird things happen this weekend when the temp dropped into the 20's



when turning the key to "on" and the lift pump cycled, the Indications I had could only be that of the VP44 bypass Relief lifting.





This is what happened. The lift pump cycled. Pressure built to over 15psi, and then dropped to 12 psi at the same time the lift pump audibly increased in RPM from the drop in discharge pressure. I can only assume that the VP44 bypass lifted off and blew down to 12 PSI.



This has never happened when the temp was over 40F.



With the engine running fuel pressure is at 14 psi.



Just something to note.

Diesel freak, I used to have this happen alot too at 20 degrees and colder, I think it is the spillback on the l/p opening and closing, this is an oem feature that is a small spring and a little stealie check valve , it is designed to keep continuious flow thru thr l/p and it makes the l/p a wet system, when the spillback opens up the fuel goes into the electric motor housing , I cant possible understand how Carter thought this would be a good idea but its there.

Like I said I used to have this happen alot but not since I re did my fuel system, I now feed the l/p with my auxillary tank from a bottom port I had them put in, this gives the l/p a possitive psi instead of a vaccumn, I also filter it before it hits the l/p thru a 90 gpm spin on set up, it filters down to 10 micron. Havent had any trouble since the bomb



cheers, Kevin

 

[Diesel Freak]

That is what I thought. The more viscous fuel caused pressure to rise enough to lift off the VP44 relief.



Carter is using the fuel to cool the lift pump.

 

[Whitmore]

Diesel freak

Yes the vp has a relief but my problems were in the l/p itself, my theory is that the cold fuel couldnt be sucked from the oem tank quick enough so the spillback opens on the l/p to keep it in fuel thus starving the vp... ... ... ... ... ... . jmo



cheers, Kevin

 

[Diesel Freak]

Once the engine starts fuel pressure is back up to normal. The VP44 was not getting starved in my case. I would hope the Carter pump bypass opens sooner than the VP44 Bypass relief in order to keep the Carter pump from overheating... that I why I was wondering what it's setpoint was.



Once everything warms up, it does not happen. The only reason I think the VP44 relief lifted is because it is supposed to lift at 14 psi. And since Blowdown is usually 80% of lift pressure the 12 psi on my gauge seems accurate.

 

[Diesel Freak]

Originally posted by Diesel Freak

What happens to the flow rate and discharge pressure of a positive displacement pump when you raise and lower a restriction on its outlet?

so, who is going to answer this for me? Oo.

 

[Cummins4Life]

For a gold star....

I'm gonna guess and say flow rate and discharge pressure remain the same. Oo.

 

[Diesel Freak]

Re: For a gold star....

Originally posted by Cummins4Life

I'm gonna guess and say flow rate and discharge pressure remain the same. Oo.

well... . you are half right. Flow rate stays the same, but if the outlet is throttled, discharge pressure will rise and fall with changes in throttleing



A Positive Displacement pump has a set flow rate that is directly proportional to the speed of the pump. More specificly the volume is constant for each full stroke of the pump regardless of any flow restrictions.



A positive displacement pump's discharge pressure is system pressure.



The pump curve for a positive displacement pump is for all intents and purposes a straight vertical line when plotted.



Take for instance the VP44 on my truck. It is rated at 107mm^3/stroke at 2700 RPM at rated full power of 245 HP.



Nothing is done to affect the engine except for installing larger injectors and a boost module to prevent the ECM from defueling from stock.



With that said the VP44 is still pumping 107mm^3/stroke at 2700 RPM, and is still fueling the same as if it had stock injectors, however the only difference is that more of the 107mm^3 of fuel is injected into the combustion chamber by the larger injector. The flow rate (duty cycle) of the VP44 has not been changed! It is still pumping the same ammount of fuel as stock therefore since it is still pumping the same volume, inlet pressure will not change

 

[J.R. Adkins]

Originally posted by Jetpilot

I have to agree with J. R. here. I have seen large injectors make a huge difference in the fuel pressure. Including pulling it down to 0. In fact I think that we have found the limit on fuel that the VP44 will deliver. I have gone to larger and larger injectors but now I don't seem to be able to make any more HP even with more N02 and larger injectors... ...



Doug

But without NOS OR propane you can still make more power with a larger charger. Where is KwicKKurt at when you need him? Give us a larger single charger that spools well WE NEED MORE #2 POWER!!LOL







J. R.

 

[Jetpilot]

J. R.



You are correct that with a larger charger one could make more HP. But I think with all the air you can supply the vp44 will only deliver enough fuel for around 750HP. I happen to use N02 for my additional oxygen at the moment and that is where I am coming from.



Doug