Engine/Transmission (1998.5 - 2002) Fuel pressure. How much is too much?

[JCyrbok]

I'm thinking of putting either a pusher or a Stanadyne Fuel manager system that will increase fuel psi up to the injection pump. I only want to add about 6-10 psi that will get me up to about 18-22psi at idle and hopefully keep the psi up under WOT. Is there a un safe upper limit for the psi going to the injection pump? I assume that if the psi is too high the the overflow valve would just return the fuel to the tank. Will this inturn wear out the overflow/return valve? It seems like most of the posts on fuel pressure regards too low. My truck is pretty much stock but I'm looking for the added insurance of not losing a lift and then injection pump. ANy ideas or comments would be appreciated.



ALso has anyone had any DC warranty problems with a pusher or moving the stock pump back by the tank ( which is another option for me). Any one using the Stanadyne fuel manager auxillary lift pump( that was in TDR #38)?Comments?



Thanks in advance

J-

 

[Ncostello]

Others will be able to expand on this but the maximum you would want would be 18-20psi. Beyond that, some seals in the VP can blow and ruin the pump. Some may say 20psi is too high while others have ran with pressure greater than that. This is what I gathered after reading alot on the subject.

 

[jerrethomas]

i would keep the pressures pretty close to stock. i just watched a video on the vp44 and it said that anymore then stock fuel pressure could cause hard starting. that movie was on the cummins virtual college.

 

[KatDiesel]

Originally posted by jerrethomas

i would keep the pressures pretty close to stock. i just watched a video on the vp44 and it said that anymore then stock fuel pressure could cause hard starting. that movie was on the cummins virtual college.

ECM takes care of that with the proper software which is why people with extra pushers tap into the OEM harness to get the command from the ECM on how long to run. If you just add a second pump into the system and have it running full bore then yes it will cause hard starting.

 

[jerrethomas]

Originally posted by KatDiesel

ECM takes care of that with the proper software which is why people with extra pushers tap into the OEM harness to get the command from the ECM on how long to run. If you just add a second pump into the system and have it running full bore then yes it will cause hard starting.

10-4 on that

 

[Rob Thomas]

Originally posted by JCyrbok

ALso has anyone had any DC warranty problems with a pusher or moving the stock pump back by the tank ( which is another option for me). Any one using the Stanadyne fuel manager auxillary lift pump( that was in TDR #38)?Comments?



Thanks in advance

J-

The dealer gave me some guff about the pusher pump, but in the end they did warrent my lift-pump, but I'm sure not all dealers will be so gracious.



Later, Rob

 

[Whitmore]

Her's what I know

DC and Cummins have set a lift pressure of 15 psi and the internal relief of the vp is set at 14 psi to return back to the tank, so going by that I would think that any psi over 15 is unnecessary, you will be putting extra pressure on the seals of the vp.



Here is my take on the whole issue, we really want to have a minimum of 10 psi at idle according to DC and a minimum of 6 psi at WOT. The 6 psi at WOT is to insure adequate supply to the VP so it can feed the injectors as well as cool and lubricate the VP. Of course we all know that but what I am getting at is these pressures are what DC and Cummins have set as standards to do the job, so why would we want more pressure than that ? I know many are doing it with different pumps and with series pumps BUT if you stop and think of it flow is what we are really after, yes pressure comes with adequate flow , the bottom line is that it is alot easier to measure psi than flow so thats why they measure the pressure. In all actuality if we have enough flow to supply the injectors and cool , lubricate the VP than thats what we need.



JMO but I really think the guys running without a regulator @15 are jeopardizing the life of the VP.



The pushers have proved to be a better and more reliable fuel supply and I agree with what some folks are doing but I do not agree with the higher pressures.



If your tires say 80 psi is max than would you run with 100 psi just because ???



cheers , Kevin

 

[Roger rodbolt]

Re: Her's what I know

Originally posted by Whitmore

JMO but I really think the guys running without a regulator @15 are jeopardizing the life of the VP.



If your tires say 80 psi is max than would you run with 100 psi just because ???



cheers , Kevin

Kevin,

Please don't take this as sarcastic , but if I were going to overload my tires by 150% like I do my engine... ..... yes, I would pump them up to 100psi. Not a good idea for sure but neither is making 500hp with 15psi through tiny (stock) lines connected with restrictions. The stock lift pumps weren't good enough for stock horsepower so DC upped the pressure to 15psi. I've been running very high LP pressures on '98. 5, the worst of the VP44's, with nary a problem. I've seen VE pumps leak, P7100 pumps leak so I'm sure that there are seals that have leaked in VP44s but I'm not aware of any. How many VP 44's have leaked due to pusher pumps?? Real numbers? If the VP 44 has a 14psi internal relief valve, would this protect the pump from high pressures? Larry

 

[Whitmore]

Roger

Point well taken, I do understand where you are coming from but



IMHO stay with 15 psi and work on the volumn of fuel, the reason the pressure drops when you WOT is because there is not enough volumn of fuel there.



Here is my setup, I use my aux tank as my main feed, I am comming off the bottom of the tank thru a big spin on filter rated to handle 90 gpm at 10 micron, then to my oem lift pump and the oem filter to the vp, only thing I have up graded so far is Ray's banjo bolts, with a positive head feeding the lift pump instead of a vacumn it made all the difference in the world, my lift pump is just cruzin, no strain there. At WOT I cannot pull below 10 psi at the vp, I think my lift pump will last a long time with this setup.



Here is where my thinking came from, in the fire dept on a class A pumper if I can get a good volumn of water to the suction side of the pump I can do anything I want with my pressures, thats why we use 5 and 6 inch suctions, now if I were to use a 3 inch suction, the pump would run away from the water and cavitate the pump therefore you cant make no pressure.



cheers, Kevin

 

[Roger rodbolt]

Kevin,

Yes, I believe that you are right on, the VP 44 needs full volume of fuel available. You can get the same volume by using small lines and high pressure or large lines with lower pressure. The lower pressure/larger lines shouldn't have any drawbacks if you disregard time, money and finding a single lift pump that will keep up. Most of the high pressure setups were done piecemeal as we increased horsepower. I prefer the single pump/ high volume/ low pressure system but since what I'm running works it's easy to work elsewhere.



I will say that I'm not a fan of banjo bolts, though. Larry

 

[Steve St.Laurent]

Kevin, where did you get the 10 psi @ idle and 6 psi at WOT spec from? I have talked with several mechanics that have directly talked to the STAR hotline and I have also talked directly with people at D-C and have been told that the ONLY spec they are using now (and have been for at least the last 6 months) is 8 psi under load at WOT. If it's below that they tell the dealer to replace the lift pump.

 

[Whitmore]

It states right in the service manual that (69kpa) 10 psi at idle and 7 psi while cranking mode of 25% duty cycle , the 25% duty cycle during cranking is to protect the vp from over pressure since there is NO fuel usage.



The 6 psi @ WOT came from the Cummins guy here in town,



Myself I think that 6@ WOT is still sufficient i it doesnt get any lower and the pressure comes back once up to speed, now if you are on a grade with a heavy load pulling hard I think that 8 psi is a minium psi, D/C wants 70% return to the tank, thats alot of fuel!!!



One more thing I would like to add and that is to do with the cooling and lubricity of the vp, MASS FLOW is the answer not psi, now true if you have 0 psi than obviously there is no flow but I can tell you that mass flow and volumn are basically the same thing, the ultimate answer is in the extra fuel not being consumed by the injectors, this extra fuel is being circulated thru the vp only for removing the heat generated from the pump and also to lubricate the moving parts of the vp not to forget the o-rings and rubber components, without this extra fuel circulation the vp is toast.





Let me tell you a related story about mass flow, at my job we built a 350 million dollar plant that has a cooling loop of glycol for many many large pieces of equiptment, we were having trouble getting the cooling system to operate per design and I was assigned to trouble shoot and fix the problem, I went to the fartherest away piece of equiptment and looked at the roto meters, they were barley turning, not much flow here, supply or return, anywaty we ended up with different impellers for the pumps to create addequate flow, then the roto meters turned good , mass flow was taking the heat away, now on the supply line I showed only 3 psi, I experimented and pinched the valve till I had 10 psi on the inlet pressure and took temp readings of the big compressure , I came back in 30 minutes and the temps had climbed 18 %, I then opened the valve 100% and came back in 30 minutes and the temps were back down again, MASS FLOW not PSI is the answer.



I only wish I could afford some flow scan meter so I could see in the cab what my flow on the return line is.





cheers, Kevin

 

[Gary - K7GLD]

"I only wish I could afford some flow scan meter so I could see in the cab what my flow on the return line is. "





It's already been done FOR you!



Do a search on this site for "the ultimate VP44 thread", and you will get the info yer looking for...

 

[Whitmore]

Gary, I want to monitor my flow all the time in addition to my fuel pressure.



cheers, Kevin

 

[Gary - K7GLD]

I suspect that after going thru the drill of running thru the gears, idling, towing, the flow meter would be pretty useless for anything other than occasional monitoring - pretty much like the ampmeter on the dash - nice to have, but not paid much attention to...



BUT, if you do come up with a setup and install it, sure would be interesting to see what your initial findings are... You sorta need 2 of them, one for total flow to the VP44, and another in the fuel return line...

 

[Whitmore]

BUT, if you do come up with a setup and install it, sure would be interesting to see what your initial findings are... You sorta need 2 of them, one for total flow to the VP44, and another in the fuel return line... [/B][/QUOTE]



Gary, you are exactly right, they have one that is duel service, measuring flow to the vp and thru the return, thats what I want but it is $$$$ big time



cheers, Kevin

 

[Big_Daddy_T]

These pusher pumps are high volume low pressure. They serve two purposes. Keeping the fuel supply to the lift and increasing the volume. The increased pressure is a side effect. I can still make the pressure drop to just above acceptable. About 11 Psi. when we increase the volume the resistance in the pump brings up the pressure. I doubt that it can be rectified. I dont think you will be able to increase the volume, to the level of our demands, without bringing the idle pressure above 15psi. I think some folks lifts were making up to 18 psi at idle. Thats the stock lift pump.



A bosch mech said 24 psi if I remember right. Above 24 The pressure is detrimental.

if 8 psi is a bad pump what is a good pump. 10 at wot? So even with a pusher Im only 1 Psi over good at wot.



These pumps are used in other applications with much higher injection pressures. They are overbuilt for our application.