BarryG

There have been several threads on keeping the vp cool during operation as well as at shutdown. Some have tried cooling the fuel both inlet and return. I have not seen anything definitive about the efficacy of it actually doing anything. Obviously cooling the fuel does little if anything for heat soak at shutdown. However some have rigged up bilge blowers or other type fans set on a timer to run 30 60, and even 90 minutes with ducted air to blow over the vp from outside the under hood area after shutdown. If I recall there was a definite difference in how long it took to cool it down but can't recall if it did much to lower peak temp. Nor do I recall any real follow up as far as longevity

Modifying fuel system so temperature to vp ..... Is name of a thread on the tdr about this it is quite extensive with a lot of testing. There is also another thread over there called pumps,lines and whatnot that has some very interesting info also with some good testing regarding the vp

KATOOM

Glad you pointed that out Barry. I addition to what you said..... Of the experiments to cool the fuel, using a cooler added more room for leaks and reason for more gelling in the winter. Both big problems. Understanding that the fuel must move though the VP to cool it and the VP allows little to no fuel to pass through unless the engine is turning, there is little point in trying to cool fuel since running temps arent the problem. So adding a fan to cool the VP after shut down was tried but finding out that the fans able to push enough air will quickly deplete the batteries if left on for the time it takes to do its job. All the modifications and experimenting people do is great, but no one has come up with anything very worthy.

dennismorgan

I,m going to throw another monkey wrench into the equation,I believe the temperature of the electronics get higher than anyone could imagine.The fuel flows through one little corner of the vp,not very effective for cooling the entire mass,the fuel flows no-where near the electronics,the electronics themselves produce heat.I believe the majority of the cooling takes place from the fan blowing outside air over the VP.If you want to eliminate heat sink,LIFT YOUR INSULATED HOOD,last time i checked heat rises.I also believe running temps on hot days,especially towing are exceeding healthy vp limits.Now for solving part 2 of the proplem.How about finding a way to lock the clutch fan for more air flow through the engine compartment.It would effect your mileage slightly but put a continuous 10,000 CFM of air through your engine compartment.

KATOOM

I see why you would think this but in actuality the fuel runs completely under the heat sink and through the VP before it exits the overflow valve. Looking at some diagrams gives an impression otherwise so again, I can see where you'd think that. If it was only air that cooled the VP then it would ALWAYS run about as hot as the engine.

bentwings

I know this is bit of a dated thread but here are a couple questions.

I'm a mech eng by trade and ask lots of questions...my favorite is "show me the data"

So, driving 60 mph I get 20 mpg consistantly and over the same route. therefore I burn 3 gallons of fuel per hour. The lift pump, if it runs all the time can probably supply 12 gph at 13-15 psi. So where does this excess go?? The Carter and Holley vane pumps have internal regulators that simply bypass the excess and return it to the inlet side.

Now, since the VP-44 is receiving fuel at 13-15 psi and assuming everything is functioning properly, uses 3 gph and bypasses some unknown amount thru the "mystery orfice" in the overflow system back to the fuel tank.

So has anyone actually measured this bypass volummn?? Is it 9 gallons in this case or some lesser amount??
Is it hot??

I have measured 130 deg on the bottom of the tank with it about 1/4 full after an extended trip with the trailer. Initially I thought this was due to bypassed fuel but I think the there is a lot of heat from the radiator and motor going under the truck. Even the spare tire was much above ambiant temp. Our fuel tanks being plastic are poor conductors as well as emmitters of heat so it would seem that some of the heat is comming from heated fuel. This because of it's proximity to the hot motor and injector pump. Certainly there is not a lot of pressure in the return line however it is possible that the VP is pressurizing the fuel then using some and reducing the pressure to return it to the tank perhaps cooling the pump some in the process. The pressurizing being the cause of the heat.

My streetrod has a Holley Blue pump and I can get pretty bad mpg (high flow without pressure loss) with the supercharger doing it's thing. However sane cruising at 60 mph shows the aluminum fuel tank in the trunk never much above ambient and often 10-15 deg less as it is away from the sun light and under car heat. I also have AN 8 aluminum lines including a return line so fuel is constantly circulating thru the fuel pump. I'm sure that the tank and lines provide some cooling. The point being that in this case the fuel system is flowing all the time as opposed to our trucks being restricted by the "mystery orfice".

BarryG

Bentwings earlier in this thread I mentioned two threads on the tdr (both of those threads are many many pages long otherwise I would have tried to cut and paste the info) they did do some testing of return flow from the vp and it is quite significant. I do not know where they got the return flow from I assume at some point past the engine ie at the tank via the return line but it may have been farther upstream. If I recall correctly, and possibly aren't, regardless of inlet pressure to the vp the return flow was the same quantity. In any case here are links to those long threads. Hopefully you can access them through here. The first one deals with vp pressures and return flows the second deals with trying to cool the vp with various methods

http://www.turbodieselregister.com/f...+lines+whatnot

http://www.turbodieselregister.com/f...modifying+fuel

edit - I just tested the links and it takes me right to them however I am a member over there as well as here so it may be different for nonmembers though I know nonmembers of tdr can look at threads but not post or search so still not sure it will work

KATOOM

bentwings I'm not sure exactly what you're asking..... Are you wanting to know how the bypass system of the fuel pump works, or the exact volume of return fuel, or the where the return volume is coming from and how it gets through the VP, or why the fuel gets as hot as it is? Or all of the above..... But in saying that, what does this potential mystery orifice have to do with any of the noted questions, because even if there was such an unknown orifice, why would it be the restricting source over any other portion of the supply side of the fuel system? Thats not me being demeaning either but rather that you have my curiosity up in regards to your new found questions.

So if I can add to any of them:

The bypass system would be specific to whatever fuel pump you're using. The OEM lift pump has a check ball and spring setup which was notorious for the ball hammering its way into the pump housing and causing a loss in fuel pressure over time.

The return fuel from the VP "does" actually pass through the entire VP as you'll see in this picture.



The rest of the fuel comes from the excess fuel from the injectors.....and is probably pretty warm and toasty, as you pointed out too. So in saying that, the fuel from the injectors and head is at least 190* and the VP compresses fuel and creates heat in the process as well, which tells me that the return fuel must be kinda warm and will over time cause the entire fuel tank temp to rise. Hot how will the fuel in the tank get? Well I'm not really sure but I'm only guessing that given the volume in the tank is going to offset the returned heated fuel, and as the plastic tank hanging out under the truck dissipates heat, it cant be too hot but definitely can be warmer than ambient. In saying that too, remember that the return fuel is dumped directly into the fuel module canister which is where the fuel pick up supply is located as well. So if the return fuel was terribly hot then the supply line would be sucking up hot fuel and re-circulating it back through the fuel system only to be repeated over and over and getting hotter and hotter.

In your comparison to your supercharger (awesome) street rod, the fuel system isnt the same as your hotrod isnt fuel injected with a fuel injection pump and dont run fuel pressures anywhere close to what your truck does. So those apples and oranges arent a good comparison and explains why your hotrod fuel is so much cooler than your trucks fuel.

In regards to return line pressure, I've battled this topic before over the fact that everyone desires the higher volume 150 gph fuel pumps over the lesser 100 gph fuel pumps. I think that trying to cram all that fuel could pose a problem as possibly the fuel cant return as fast as its being shoved in there.....which thinking can potentially cause a problem with the VP expelling hot fuel as fast as it should be allowed. But as you so pointed out, "show me the proof" has me wondering if its a problem at all since there seems to be no related failures to excessively high inlet fuel supply pressure.

Have I helped.....or made things more confusing?

lovinCTD59

Great ideas and thoughts! Subscribed

bent valves

For years the internet folklore has said that you need a minimum of 10 PSI from the lift pump to properly cool and lube the VP44. A higher pressure will flow more fuel through the VP44 and provide more cooling.

For years I have disagreed with the folklore. Let me use the diagram of the VP44 provided by KATOOM to make my argument. The lift pump fuel enters the injection pump where I labeled "Fuel in". Notice that the lighter blue/gray passages are at the lift pump pressure. The VP44 internal rotary vane pump receives fuel from 3 sources as shone by the arrows. The "Fuel in", fuel returning from the timing advance mechanism (the lower light blue/gray passage), and fuel from the VP44 spill back valve. The darker blue passages in the diagram are at a higher pressure and the fuel in these passages come from the output of the internal rotary vane pump. That spring loaded spill back valve near the top of the diagram is needed to limit the internal pressure to about 135 PSI. (I have not measured this pressure but found reference to it in a Bosch manual.) All fuel entering the VP44 must pass through this internal vane pump. There is no sneak path to allow more fuel to leave the VP44 and flow back to the tank.

The internal vane pump is a positive displacement pump. This means that the volume of fuel entering and leaving the pump is the same and is controlled only be the speed of the VP44 input shaft. Many people argue that a higher lift pump pressure pushes more fuel through, but it does not. The fuel cannot be compressed like air and a rotary vane pump cannot pass more fuel than its designed displacement. (A worn pump may leak a few drops of fuel by the vanes.)

The high pressure pump marked with "2" in the diagram is responsible for creating the 17000 to 20000 PSI fuel pressure needed for the injectors, "5". Items "4" and "3" are the fuel distributor and dump valve. Just above the number "3" is a spring loaded accumulator that stores fuel under pressure to provide a pulse of fuel to quickly fill the high pressure pump before the next injection event.

The injection event will almost always not use all the fuel available from the high pressure pump. The computer controlled dump valve sends the extra heated fuel back through the banjo bolt to the tank. When you tap the wire on the VP44 it is the dump valve that gets held closed longer to inject more fuel.

So now some questions. Why does the VP44 need a minimum of 10 PSI or more at all times? How does increasing lift pump pressure aid cooling and lube of the VP44. If the answer to these questions are true, it would mean increasing lift pump pressure will return more fuel to the tank and that has been proven not to be true.

BarryG

Dave
What you are saying is pretty much the same conclusion the testers on the tdr thread above found with a flow meter on the return line. Same return flow regardless of inlet pressure at a given rpm. So the higher flow pumps may have increased the pressure but it wasnt going through the vp otherwise the increased flow would have resulted in more returned fuel. So the increase in pressure was due to increased lift pump flow backing up so to speak as the vp can only ingest and expel so much and it appears to be a fixed rate at any given rpm. Reduced pressure in this case does not necessarily mean reduced flow. I believe in one of the tests the inlet pressure was 0 and it still produced the same level of return flow through the flowmeter.
One of the testers early on was a vendor and got into it on his own thinking he could make money selling fuel systems to combat the supposed problem. However after his own testing he came to the conclusion that there really was no problem with the fuel system outside of the fact that the carter pump was too far away from the tank and was pulling instead of pushing fuel.

dennismorgan

Wow,you guys are shaking the very foundations of the entire after market industry and dodge forum guru,s.It would seem the facts presented from both sides would suggest that it is not only the mysterious orifice,but the mysterious vp44,because it appears from my perspectives both sides have valid data.Katoom pointed out, trucks that run higher fuel pressures have fewer vp problems and trucks that have low and weak fuel pressures are always in getting rebuilt IP,s.Conversely zero inlet pressure showed same return flow rate.I only have one option left, read the tdr data for myself before i check myself into a mental care facility.

bent valves

A man much wiser than me said:

"Nothing is easier to fool than the human brain. You do it to yourself all the time. True objectivity is impossible without the use of measurements that are independent of the observer."

So If you want to know who is right, more fuel pressure will aid in cooling and lube, or extra fuel pressure does not help to cool and lube, the answer is simple. Disconnect to output of the VP44 and use a short tube from the output into a bottle. With the engine running at idle measure how long it takes to fill the bottle. Now increase the lift pump pressure and repeat the test. This measurement of how much fuel flows into the bottle has been proven to be the same and this disproves the hypothesis the more lift pump pressure helps cool and lube the VP44. But don't believe me try the test yourself.

Another wise man once said:

If you read it on the internet, it must be true.
.................................................. ....................Abe Lincoln

HOHN

This is where I'm at ^^.

My STOCK LIFT PUMP is still going strong-- 11 years and all. Pressures are anywhere from 5-6 with cold fuel to 12 or so in the summer with a clearn 7 micron filter.

I've had a fuel pressure gauge on my truck over a decade. I've always had good pressure to the VP. I lost a VP at 40k miles back in 2005. The replacement pump is still powering my truck every day. It's only 94k miles now, but LOTS of thermal cycles-- a brutal duty cycle of almost nothing but short trips.


I recall those all TDR threads when the DTT gang went for test drive with the flow meters wired up and only say 30gph to the return regardless of inlet pressure.

I'm of the mind that if you have positive pressure to the VP at max fuel demand, you have enough fuel.

HOHN

Btw, it's nice to revist this topic after not being on DTR for a couple years. It's like reliving the VP glory days when we were all experiementing with Diesel Dynamics honed injectors.

Man, that was forever ago!

BarryG

Dennis
Lets be careful not to read too much into anything. 0 pressure with flow is one thing low pressure with low flow would be another. I am not suggesting that poor lift pumps wont take out a vp44 and the carter lift pump seems to have proven itself to be unreliable. I myself have had three fail and have quit using them and Hohn states his is 11 years old and still going fine. And perhaps my blanket statement of being unreliable is even overstated. How many people own the trucks, how many people lost a vp to poor fuel flow from a worn out/broken carter lift pump? Or was it the electronics that went out on it? Or was it some other malfunction within the pump that didnt have anything to do with pressure or flow. On the forums you will certainly hear about the failures but few would start a thread stating that their lift pump or vp is going well.

I am by no means an expert however the testing in that thread and one two others from way back when is the only information I have ever seen with actual measurements and not just conjecture, speculation, educated guesses and armchair mechanicing. I am in no way trying to bash anyone who has done the above I know I certainly have we all try to figure out our problems with the info we have at hand or have heard from someone/somewhere else or our own personal observation and put 2 and 3 together and gotten 4. Sometimes we actually confuse the issue with more than one thing which are actually totally seperate such as 0 pressure but high flow vs 0 pressure and no/low flow how do you know the difference unless you tested the flow which few are willing to do, fewer yet that actually try like into a bucket or something and even fewer who would actually hookup a flow meter and get actual flow and having the data to compare to what it should actually be its not like everyone has one of those lying around in the garage. The only real thing that thread did for me was tell me that higher pressure or high gph pumps do not add to or aid in the cooling/lubing of the vp.

Hohn
long time no see post
as I recall you had a comment or two in the original. Hope all is well with you and yours, looks like your still with Cummins hope that is going great for you as well.