Brownie,

This is an awesome question, but alas, I can't help you with it yet. I have not had time to look at the relief, though I theorize many of our problems are located here. (have yet had time to prove them out.)

So hoping to bump you up and see if someone can shed more light on the topic!!

Hag

 

http://www.cumminsforum.com/forum/98-5-02-performance-parts-discussion/537213-vp-info-new.html

Other food for thought from a different point of view, follow the link within this link :thumbsup:

 

Factory VP44 overflow valve is fine. You don't need a adjustable overflow valve. Because what your aiming for is getting the overflow valve open to return the heated fuel back to the tank not trying to close it and hold pressure.

 

I've spoke with a number of VP44 specialists across the country over the phone in the last week. They tend to agree with you. They're more fixated on having flow through the VP44, not so much maintaining a certain pressure (as long as that pressure is above 5psi). Apparently the stock carter pumps drop down to roughly 5psi at WOT and maintain just above 10, so they're telling me my fuel pressures aren't abnormal. I'll be upgrading my fuel system regardless down the line to get some credit in my engineering class, but for now I'll just run it as is and make sure I'm maintaining some pressure. Not really too worried about cooling; I live in Alaska and most of the time the fuel flowing to the injection pump will be at sub-freezing temps. Should be plenty cool at -20degF. Maybe a temp sensor on the VP44 would be a decent idea...

 

VP44 already has a temp sensor built in.

Also I don't agree with the 5 PSI number at all. Even Bosch doesn't suggest it either.

From my write up.
Mopar1973Man's Dodge Cummins Articles - Fuel Pressure Specification For Bosch VP44 Injection Pumps

I've seen several times where people will link back to performance pump builders and quoting where they say, "(Un-named) proved that 5 PSI, under load, made all the horsepower the VP44 pump could make, even with stock fuel lines, fittings and supply pump." This might be true but there is nothing ever said about the life span of the pump at these conditions. So... Please do not follow these performance crowds into destroying a perfectly good Bosch VP44 injection pump.

The fact still remains from Bosch the actual designer of the Bosch VP44 injection pump states that injection pump should return 70% of the fuel back to the fuel tank for cooling and lubrication purpose of the VP44. Being the only way a Bosch VP44 injection pump can do this is to have fuel pressure above 14 PSI to open the overflow valve. Then if the stock Bosch VP44 injection pump with an enhancement box say an Edge Comp on 5x5 can consume 15-20 GPH that means the stock 35 GPH pump cannot keep up with Bosch's design of 70% return volume. So this why products like AirDog, Raptor and FASS was created because they actually meet the demands of the Bosch VP44 injection pump. Then another fact that Bosch will let you know of is that diaphragm damage occurs from operating the Bosch VP44 injection pump at low fuel pressures. Making matters worse is that no Bosch injection re-builder will void warranty a VP44 injection pump with diaphragm damage. Dead give away that you had a bad lift pump or low fuel pressure problems.

Then the other fact is right from the Dodge Factory Service Manual has the minimum fuel pressures (picture at the top of the page). It even states the pressure that the overflow valve requires to open. Refer to the Overflow Valve Testing from the Dodge Factory Service Manual and see that the overflow valve should remain closed at 10 PSI and open by 14 PSI. So if the overflow valve is close by 10 PSI, then you extra cooling and lubrication just disappeared.

So ultimately it suggested to have a fuel system of no less than 100 GPH supply that can maintain a minimum pressure of 14-15 PSI at WOT. This will great extend the life of the VP44 because it keeps the electronics cooler longer and keeps the rotating parts lubricated properly.

So please people let the facts and information from the actual designers of the injection pump (Bosch) and engine (Cummins) provide you proper information for your fuel system for your engine. Don't be swayed by performance shops claim of high horse output with little fuel pressure. As I proved right here doesn't work for longevity of the VP44 injection pump...

 

jmd,

(didn't see you guys responding. whilst I was taking so long... hope I didn't contradict anyone/thing)

Glad you found that post!!!! That is the one that I have been working with mike on to replicate and understand better. (I still owe him at least one tall cool one...!)

Pressure and flow are two totally different things.... easy to think of as comparing the 3 inch off of a fire truck running at 150psi (will fill your pool in less than an hour), or your home pressure washer delivering 2200psi (might fill your tub in less than an hour).

The VP is cooled by flow, not pressure. We have come at it backwards by saying "you must have 15psi to blah blah blah." No, we assume we need 15 psi (or Xpsi), to have the flow we need. (I still have not gotten good flow/head curves on the different lift pumps, trying but not much published. will have to set up my own test bench apparently)

Bosch does tell us the VP works best in a certain pressure range, (hence the reason they installed the relief valve in the first place.) They assumed the LP would build enough pressure to open the relief, and bleed the extra back to tank, cooling the VP in the process. During High fuel use, the relief valve would/should close, trying to maintain pressure whilst sliding down the back side of the flow/head curve.

Hoping to figure it out one day, it is on my list, just not there yet!!!

Hag

 

Well, in that case, it brings me back to my original issue. I think the Overflow valve might be opening prematurely. I guess I need to get a rubber tip for the air compressor and double check. I just can't believe that a Carter rotary vane pump can't make more than 12psi when it's rated for 18psi. Complete waste of money. Can I slap one of these Walbro 255's on there? They make a ton of pressure, but I'm assuming that extra flow might just pass through the now open overflow? Maybe the overflow is too restrictive and I will over pressurize the VP44. I dunno, I'll replace all of my lines and put the 2 Carters I have in line and see if it gets better. Really don't want a $600 AD or a $1300 VP44.

 

The other half of the pressure swings is the plumbing is too restrictive. So if you upgrade to Vulcan Big Line kit and relocated the lift pump back by the tank you would have nearly a perfect world. The stock lift pump will keep up with a stock engine easy with a 2-3 PSI fall.

I ran this setup for a about a year but got tried of tossing money at pumps about every 6 months. That the only reason I upgraded to AirDog.

 

I have a walbro if your interested. I sent you a pm. It worked great for me. I just installed an Assassin because I prefer a mechanical pump.


Sent from my iPhone using AG Free

 

This is where I keep failing too. it is "rated" at 18psi. At what flow rate? (that is possibly "dead head" or zero flow.) None of the pump manufacturers produce (or really they don't distribute) the proper flow/head curve that would help us identify these problems.

We need to know (by actual flow measurements) what flow is going on.

I feel that if I supplied the VP with the actual minimum pressure required (which is according to Bosch seems to be anywhere from 6 to 10 psi) at a flow rate in the 200 gph (gallons per hour) OVER the actual engine usage, temperatures would be fine. We presently just use these high pressures (and hopefully high flows) to keep the overflow jammed open, and it just becomes a restriction and therefore flow restriction which we monitor by "seeing" a high pressure.

I have considered two carters in a parallel setup. (then I worry about the fact that one may push into the other, so then you need two check valves, which restrict flow...)

Have considered a low pressure accumulator, which would supply extra flow during WOT operations....

I think it matters not if you keep the bypass opened continually. We don't need the fuel to dwell in the pump, just be there when you need it, and flow through to cool it. Most people basically are doing that, jamming the bypass open. You just don't want to see super high pressures on your gauge because you are basically seeing those pressures in the pump, and it is obvious that especially during starting, high low side pump pressures seem to hurt starting.

I am a bit worried about my future tests, as the system may not function exactly as my mind's eye think it does. I also am not certain how the injector drain flow changes the return line pressure, and therefore its effect on the operation of the bypass and therefore pump discharge pressures.

Hag

 

Hi guys I've been experiencing high fuel temps on my 99 with edge juice. Around 130f and it's only 23 c outside in Ontario Canada. I had a spare overflow valve, I took the orings off and torched the spring for a second or two , which weakens it.. Now r opens at 5psi. Installed it, set the fass to 13psi and flamed it up seems fine. I'll take it for a rip tomorrow.

 

I'd suggest replacing that valve you just altered asap..... The real purpose of the overflow valve is not fully understood and its believed to be there in order to assure proper running pressures within the VP's pressure chambers. You changing those parameters may cause not only performance issues but also reliability issues.

 

This should be interesting!

 

So everything worked ok, except I was able to draw from 13psi to 7 or less under my heavy foot... so really that overflow valve helps maintain "in pump" pressure. I'm going to look into the high fuel temp but I'm thinking the temp sensor is buried somewhere in the pump and may not reflect the actual fuel temp itself.

 

What were you pressures before? Like Katoom said, I wouldn't mess around with that. First thing to do is turn up inlet pressure, adjust that fass to 15-20 psi and see what the pressure drops to like that

 

Ya it was just an experiment.. Pressure I ran was 13 and it never went below 10 under load. Which is just fine. I used to run higher but the more pressure and more flow over all the connections and fittings = heat.

 

I think your wrong there. The heat from friction doesn't make much difference, most of the heat generated on the vp is from the computer I believe. The more flow you got the more heat is taken from the computer by circulating fuel :thumbsup:

 

Most of the heat in the vp44 is from heat soak off the engine.

The computer on the vp44 puts out almost not heat relative to the rest of the engine.

 

Alright thanks, learn something every day haha. Anyways, I think the point still stands, more flow is better cooling?

 

Even though the hot engine is keeping things warm, the temperature of the VP is created by the sheer fuel pressure which the injection pump is creating. If the engine was regulating the temp of the VP then it would run closer in temp of the engine. The computer is merely along for the package ride and isnt the heat source either. Unlike the P-pump which is cooled by engine oil, this is why the VP is cooled by the fuel passing through it. This means causing that fuel flow to remain more "stale" in the VP means it cant remove that heat fast enough which causes crystallization of the computer solder and asphalting of the fuel. Next time you drive in weather around 75 or below, when you shut the engine off, pop the hood and feel the PSG. It will be cool enough to hold you hand on it which is probably around 100*-110*. But when the weather is above 80* or so you'll find that the PSG runs a tad warmer. Triple digit summer weather and the PSG will be almost too hot to touch for very long. Even though it feels that hot, its more than likely no hotter than about 135*-145*.

That said, yes if and when fuel cycles through the entire fuel system repeatedly then its going to raise the temperature of the fuel tank which will in turn cause the overall running fuel temperature to increase. This is why you see fuel coolers on many diesel applications. But its been thought that either Cummins and Dodge figured there was no need for a cooler or that the cooling of the VP is adequate as long as the fuel pressure remains in spec. Noting too that when the fuel temp reaches 160* then the temperature sensor in the VP is supposed to trigger a limp mode. Also, this is why some people will run no less than 1/2 tank in hot summer weather. The more fuel in the tank, the more stock to offset the rise in temperature.

Lastly, there is no heat generated by fuel passing through these lines either. Physics requires far more velocity for that to happen. :thumbsup:

 

Hey guys I have been looking everywhere to figure out why I can't get my fuel pressure to come down. My lift pump went out so I installed a walbroh 255 pump back by the tank and now my fuel pressure is up at 30-32 psi so I installed an inline adjustable regulator(0-160 psi) and with the regulator set to the lowest setting the pressure is still at 26psi. Any help would be greatly appreciated!

 

I've been running the Walbro GSL-392 pump for about fourteen years with great success. I did have to replace one about ten years ago because it got a little erratic.
I do carry a spare, but it's been living comfortably in the toolbox for a long, long time.

They are capable of putting out a lot of pressure. I have a bypass regulator that bypasses back to the fuel tank and is set at about 20 psi. I don't even remember what brand the regulator is; I bought it from Vulcan many years ago.

It appears to me that the regulator is your problem; the pump is doing what it's designed to do.

 

Mike, Glad to see you back on the horse.