dennismorgan

I thought i knew the answer to this question.......UPPER LP FUEL PRESSURE LIMIT OF VP44
I,ve read a ton of posts on LOWER limit,IDLE and WOT and i think we are all in agreement on those, but upper limit is rarely mentioned.I have been given credible advise that i could damage the inj pump with to much fuel pressure,I have also been given credible advise that no harm to inj pump only there is no point to over 20 PSI.If you have had any first hand experiences would you share them and the mysterious diaphragm.

dubc2323

Well my truck has been running 21 after filter changes for at least 8 years. original vp still good and i'm at 210,000 miles now.

dennismorgan

dubc2323,thats fantastic,apparently this is the big question,why can some owners of 98 through 2002 go through life with the vp44 and is not even an issue and others like me,looking at replacing again my IP after only 30 months.Have you read the 5 pages of posts titled ,WHO,S GOT A MECHANICAL BELT DRIVEN LIFT PUMP.There is alot of great posts about this topic.So when i increased my psi to 23 my IP did not like it,I know the electronic part of my IP is bad and maybe that is part of it,but readjusted back to 13 psi at idle and runs perfect.

dubc2323

there's probably numerous combinations as to explain why some last longer than others, or part of it could just be luck. Have you tried adjusting to the 17-18 psi range?

KATOOM

Hey dennismorgan, I can completely relate and I completely understand and respect your desire to find an answer to your question but.....you wont. Before you question my answer, please let me just defend myself by explaining that even though I never profess to be the "elite" or "all knowing" about VP's but that I've been around many Dodge Cummins forums (and other diesel forums) for well over a decade. In saying that, I never accumulate my information from one or one type of source, therefore what I have learned over those years is an accumulation of many many different sources.....and personal experience.

Taking that all with a grain of salt..... The VP has NO recorded high pressure limit. There are even guys who run up in excess of 30 psi or more with no problems. Is that necessary or even advised?.....heck no, and mostly because no one really understands what that kinda psi "could" do or what other things are taking place while under that much psi. So in saying that, most have just come together to accept the knowledge that if the VP overflow valve is preset at approx 14-16 psi, and because the only way the VP is cooled is by excess fuel, then keeping the psi anywhere just above that 14-16 psi range is allowing fuel to pass through the VP, thus keeping it cooler than if the fuel remains in a more stagnate state below 14-16 psi. How stagnate?.....well thats up for debate because we're not really sure how ON/OFF the overflow valve really acts, as in saying that is 12 psi allowing some excess to fuel but just not as much as it could, or is it more shut off than not whereby allowing very little, if any fuel? Also, the overflow valve has a very small hole in it and no one really knows why either. Is it to assure that "some" fuel always passes through the VP or is it there to allow the entire fuel system to equalize or bleed down after shut down? Kinda like a refrigeration system. Remember, the VP is electric, but controlled by mechanical timing. Which is me also answering your question about your fuel system bleeding down after shutting the engine off. The fuel system does not hold pressure after shut down but acts more static than dynamic. The fuel system is more like a drinking straw in a cup of water whereby when plugging the straw and lifting it out of the glass, the water remains in the straw. Thats called a "prime" and is what the fuel system does. It always has a prime and needs that prime to assure that the VP always stays full of fuel. Loose the prime through a small leak somewhere in the fuel system and the VP then has to re-prime to restart. Thats where the "cold" hard start can come from.

So hopefully I have not frustrated you anymore than you already are, and maybe even clarified something.

dennismorgan

Katoom ,you have me convinced on the upper limit of fuel pressure.
I have been reading like a mad man and have read back posts to about page 12,i have become obsessed.You know that when i boosted my FP to 23 i experienced some strange results.I,m convinced my gauge is accurate and the method i used to increase fuel pressure was sound,so why did my IP get so hot just running around locally and my engine temp not exceeding 180.You mentioned the vp overflow valve with the little return orifice could this be it?,with the 23 psi the fuel pressure came down very slowly then stuck at 10 psi with engine turned off.When i returned fuel pressure to former 13 psi all problems went away and ran perfect and gauge behaved normal dropping quickly to zero when turned off.

KATOOM

As extremely rare as it is since its such a basic functioning part.....you could potentially have a stuck or plugged overflow valve, since there is nothing to it but a simple ball and spring. In entertaining that possibility, there is a couple things which would happen if the overflow valve did fail, and one is excess fuel temp.....and coincidentally hard starting too. But again, its so rare for it to be the problem that its hardly considered. So with that said, last time I heard, they're only about $35 from vendors like Geno's. If you're curious, you could pull yours off and either check its pressure settings and function with an air compressor regulated to the specific psi ranges, or just replace it with a new one.

SIXSLUG

Dumb question Dennismorgan, but do you keep your fuel level over half a tank?

I know some guys that are always running around below 1/2 or even 1/4 tank. If you are in a warm climate and running a low tank, you don't have the cooling capacity of a filled tank and at a higher psi the exchange of overflown fuel will be faster allowing less time to dissipate heat...

Just a thought.

I am still amazed nobody has come up with a bulletproof modification for this Injection Pump!!!

KATOOM

I agree but as much as I'm disappointed that the VP issue wasn't fully solved long ago when initial reliability was discovered..... I think that the VP's bad reputation is being fueled by history rather than current facts. With all the current VP upgrades, the newer VP's are pretty solid as long as they have good fuel supply. The only thing I can see being an issue when having to replace one is making sure you actually get one that has all most current upgrades, and not one sitting on a shelf for the past 5 years or so which may only have some.

dennismorgan

Sixslug,I have always ran my truck down to 1/8 of a tank mainly because i liked to check my mileage and ordinarily get 550 miles just running around locally.However I have discovered as you say the fuel in the tank is the only thing keeping the IP cool.I will change my habit and fill up at 3/8 or half.
Katoom you wanted to know the temperature of my IP since attaching a heat guage to my IP. On the motor I have installed a 180 thermostat and without towing motor stays below that temp.The thermometer sensor on the IP is threaded into one of the three bolt holes of the silver colored mount that the throttle mechanism is bolted to. Local driving IP stays at 130 degrees,when i shut the motor off i watch the temp rise to 160 degrees,HEAT SINK.This is not towing ,however average outside temp here is 90 to 100 degrees.Soon i want to hook up to my 10,000lb fifth wheel RV and check the temps and heat sink rates.

dennismorgan

Katoom,Your last post #9 really clears up or defines part of the overall problem.A new guy like me buys an older Dodge Ram pickup,joins a forum and asks all the same questions ,over and over and over,a continuous never ending merry-go-round.I think when absolutes, facts and solutions are realized about the weak points of our trucks we need to somehow document them as being THE NEW STANDARD.In this particular case knowing that all rebuilt pumps are not done to the same standard,they would best be described as semi rebuilt.Imagine buying a rebuilt starter or alternator where only some of the crucial parts were replaced,the rest were bench tested!I have heard the $1200 dollar rebuilt VP44 is the one you buy when you do not plan on keeping the truck,yet that is the one most everyone buys.

KATOOM

Interesting. I'm a little confused though as I'm not aware of any throttle mechanism anywhere on the VP. You couldn't post a picture could you?

As for temps, that sounds about right. Keeping the fuel tank "more full" is always best but really only necessary during the hot weather. I generally dont let it get below 1/4 ever. Yes, because of fuel heating up, and because it costs so much to fill it up. If you're only seeing 160* as the hottest after shutdown then thats not too bad. I understand that anything over 160* is when its getting too hot for that lead free solder.

In saying all that, and not to change or hijack the thread but, running that 180* is doing your motor no good. There's nothing wrong with the 195* thermostat and in reality, the 24v needs that higher cylinder head heat for optimal combustion and for optimal fuel efficiency, and hp. Especially in the cooler weather. The 12v aren't as picky. People tend to confuse the facts that a diesel is not a gasoline engine and therefore dont follow all the same rules. Heat is one of them. Now, of course there is too hot but generally if your radiator is clean (blowby bottle relocated) and the coolant system and OEM clutch fan are function correctly, you should never have a problem with engine heat. Even towing your heavy trailer on hot days.

dennismorgan

Katoom,i have my heat sensor attached on a mounting bracket for part of the VP44,really to be completely accurate it would have to be somehow attached internally inside the IP.However I have heard it said that the only part of the IP that is heat sensitive is the electronics.I have deliberately parked my truck in the sun after driving and it is holding 165 degrees at the IP.Heat sink and sun on a 95 degree day on a bronze colored hood as contributing factors.If i had a 195 thermostat in it towing, my engine temps would be 200-210 degrees,my IP would be proportionately hotter because it is bolted to the block,say 180 minimum,then another 30 degrees of heat sink when you shut it off, 210 plus,and there you have it fried electronics,fry them often enough and you have premature failure.So in conclusion we really do need to find ways to keep the VP44 cool.

dennismorgan

Apparently i,m not done.Imagine a truck manufacturer has to build a machine that is going to run in all extreme climates and conditions like heavy hauling.From 40 below in northern Canada to 120 in the Sonora dessert without changing anything.IT IS UNREALISTIC.I can see swapping winter/summer thermostats seasonally.In hot weather running your engine after you stop till the temp comes down and lifting your hood to prevent heat sink.Taking the hood liner off/on seasonally.Ensuring optimal fuel pressure.But ultimatly hopefully somebody will come up with something that we can regulate our VP44 temps.

KATOOM

Hey Dennis, I get it and I understand where you're coming from. I can only tell you that your not doing any good for hp and fuel mileage with that 180* thermostat. Whether or not it allows for less heat soak is something to be determined since at this point, its only speculation. In saying that, I do agree in thinking that a cooler engine will keep all the surrounding components cooler but I cant say positively if its going to help. Keep up the research and hopefully you'll solve something apparently unsolvable since its introduction.