fuel press for modified engine

[Don Tanklage]

stock engine, but moded pump, turbo, etc



has anyone played with fuel pressure to see if it matters?



1) how much pressure can you give one of these ve pumps?



will more pressure somehow get more fuel to inj?



i dont see how it would



2) if these lift pumps are such a pain in the butt has anyone figured out a elec alternative?



3) alt filter sys?



i have used some pretty nice mallory pumps on nitrous systems that i have built



some as high as 100 psi and a bunch of gal per hour



dont know if a fuel filter would like that much pressure but they make different pumps



have gotten a few from summit and the price varied but none were over $200



someone must have a good combo (aftermarket pump and filter sys) that will work well with these diesel engines



dont really want to dish out the 600 bucks for a fass sys if for 300 you can build something that works the same



anyone???

 

[JLEONARD]

I haven't changed mine to electric yet, but if I did I'd use a Walbro. I put one into my boat to use as a primer, filtering pump, and a backup to the diaphram on the engine (Ford-Lehman). I think it was a model 6802. Cost $100 and supposedly puts out 7 psi at plenty of volume for our needs, and has an expected life (mean time to failure) of 18,000 hours. You can do the math to figure mileage.



Others have gone the piston pump route and I might go that way on my Cummins marine conversion project. If you search the archives there is a post with all the parts req'd for the piston pump. From what they say it works really well.



Jay

 

[PToombs]

The VE doesn't like over 15-16 psi. The seals blow much over that. You get more fuel to the injectors with 15 psi than you do with 5 psi. It pushes more into the DV.

I put the piston lift pump on mine, it runs better, supplies plenty of fuel. The stock pump on my truck only put out 5 at idle, 0 at WOT. (obviously NG) Now I have 14-15 at idle and 10 at WOT. It may drop a little more when I put in the 435's, we'll see!

 

[cerberusiam]

The max pressure is around 15 psi or seals go, a pete said. At 5-6 psi it is good for about 300 hp. f you could hold 10 psi all the time that would probably be more than adequate for what we can push out of the VE.



The FASS and AirDog contain their own filtration plus fuel heating and entrained air removal. That would seem to be the most bang for the buck but it is a fair chunk of change. You can build a Walbro system cheaper but you will need a regulator when using the higher pressure pumps plus a better filtration system and then fuel heating if so desired. By the time you put all this together and integrate it the price of the other 2 is not that significant, IMO.



Pressure is not as critical on these systems as it is on the newer ones. You can push a lot more fuel to the VE than it can effciently inject. The flow at 8-10 psi with a large enough delivery line is more than adequate to meet the needs of the VE at max usable flow.



As far as reliability and simplicity, nothing beats the old piston or diaphram pump. Back to the some old question; What do want to accomplish and how much do you want to spend?

 

[Don Tanklage]

You get more fuel to the injectors with 15 psi than you do with 5 psi.





It may drop a little more when I put in the 435's, we'll see!

that is what i was thinkin! (read my other posts if you are curious where this is going)



what are 435's?



435hp inj???



where you get those? lol



thanks



don

 

[cerberusiam]

You get more fuel to the injectors with 15 psi than you do with 5 psi

that is what i was thinkin! (read my other posts if you are curious where this is going)



what are 435's?



435hp inj???



where you get those? lol



thanks



don

Whoa, hold on a minute! There are a couple of large holes in that theory.



Just increasing the fuel delivery to the IP is NOT going to increase fuel delivery to the injectors. There are 3 other thngs controlling the amount and lenght of fuel injection.



Given the VE has adequate fuel for injection, the amount of fuel at injection is controlled by pop pressure, DV size, and the amount of time the fuel port is open to supply plus the lenght of time the spill port is exposed. You can't compress fluid so just upping the supply pressure will make no difference in most cases.



There is a limit to how much fuel the VE can push effectively WITHOUT major mods to the pump. This will be impacted by injector size and pop pressure, DV size, and more specifically the size of the injection piston.

 

[Don Tanklage]

thats what i originally thought



sure seemed like my truck ran better at all throttle settings with a new lift pump tho, and that is why i asked



water is almost not compressible but some fluids actually are



i dont know how much more dense diesel is at 15 psi than 5 tho



key words in your pagagraph: given the ve has adaquate fuel



i dont think these stock lift pumps can hang once the ve has been turned up



mine used to only rev to 2500 (worn lift pump)



new stocker it revs to 3k



shouldnt a 3200 spring rev to higher than that?

 

[PToombs]

Jeez! I didn't think about it like that! Thanks Cerberusiam! What I meant was there is less chance of starving for fuel at 15 psi. Pressure is a function of flow. If the pressure is there at WOT, you have enough flow, at WOT. If you have 0 psi, you have no fuel.

A 3200 spring winds no load to 3200, fuels to around 3000.

 

[cerberusiam]

What I meant was there is less chance of starving for fuel at 15 psi. Pressure is a function of flow. If the pressure is there at WOT, you have enough flow, at WOT. If you have 0 psi, you have no fuel.

I knew what you meant but it sounded like Don was going the other way. :-laf





The pressure/flow relationship is a good argument starter at times. DC claims static flow is adequate to determine if enough fuel is available. That gets shot down when we start seeing the problems of supply side dropping to zero under a load even with adequate static flow.



IMO, you are much better thinking of flow as function of pressure when it comes to thes fuel systems. With a given size of lines and fittings we can generally gauge the flow we need by just setting pressure on the supply side. The 0 psi is kinda of a hot spot also. Some will claim that as long as the pressure is not negative there is adequate flow and 0 psi means just enough fuel is available to do the job. About the only place this is true would be P-pump as everything else is lubed by excess fuel delivered on the supply side. A truck will run decent with 0 psi but it ain't doing your pump any good as it is being robbed of lube. Zero psi doesn't neccessarily mean you haveno fuel but it does mean you have problems.

 

[Don Tanklage]

static is not running or not moving



flow is movement



what is static flow?



is that like politically correct?



lol



thanks again for explaining the fuel req of these things

 

[cerberusiam]

static is not running or not moving



flow is movement



what is static flow?

Well now, that depends on the context it used in, noun or adverb. :-laf



I didn't coin this little gem, and IIRC, this is out of test procedures for lift pumps on the gen2 trucks. Its intent is to define the flow the pump is capable of with no load or restrictions. In that context it makes perfect sense even though it is quite likely incorrect grammar.



mea culpa

 

[MEby]

IMO, you are much better thinking of flow as function of pressure when it comes to thes fuel systems. With a given size of lines and fittings we can generally gauge the flow we need by just setting pressure on the supply side. The 0 psi is kinda of a hot spot also. Some will claim that as long as the pressure is not negative there is adequate flow and 0 psi means just enough fuel is available to do the job. About the only place this is true would be P-pump as everything else is lubed by excess fuel delivered on the supply side. A truck will run decent with 0 psi but it ain't doing your pump any good as it is being robbed of lube. Zero psi doesn't neccessarily mean you haveno fuel but it does mean you have problems.

theres no way of knowing whether or not there is enough fuel at 0 psi unless your gauge also reads vacumm.

 

[Don Tanklage]

bottom line is there should be a post in this forum...



stuck right to the top of the page...



that tells the newbies what a pc of work the stock lift pump is...



and lists the part numbers for the piston pump conversion



the rich folks can go get the fass



i am sure there are some sticklers that want their truck all stock and would think it ludicrous to have to remove a valve cover to install a fuel pump and even worse to have to grind on the cover to get it to go back on



thats fine, maybe the post will explain that you cant even get the orig pump anymore, that what they sell is 2/3 the orig size



thanks again



don

 

[Don Tanklage]

theres no way of knowing whether or not there is enough fuel at 0 psi unless your gauge also reads vacumm.

if the ve made vacuum we wouldnt need a lift pump



would we?

 

[TBurow]

the ve can pull fuel from the tank, the pump is used in vw engines with no lift pump. but with 60 hp i guess there is no chance of running out of fuel.

my 96 passat with a vp44 has no lift pump and that worries me, they dont last long on cummins with a lift pump so it cant be that dependable if turned up in my car.

 

[cerberusiam]

theres no way of knowing whether or not there is enough fuel at 0 psi unless your gauge also reads vacumm.

Not really, reading vaccum just means the pump is having to draw fuel. With either the VE, VP, or CP3 that is not a good thing. The lube fuel is the first thing to get taken out of the pool. No lube will eventually equal no pump. If there is not excess fuel as demonstrated by pressure at the pump then all the fuel is being used for injection and starving the lube circuit.



By design, these pumps need a minimum of 4-5 psi at the pump inlet to insure adequate fuel for lube in a stock setting.

 

[MEby]

oh, ok I think I get it.

 

[Don Tanklage]

then my pump is probably junk cuz who know how long it had been running at next to no pressure



with the lift pump that was on there it would only pull to 2500 usually

 

[cerberusiam]

then my pump is probably junk cuz who know how long it had been running at next to no pressure



with the lift pump that was on there it would only pull to 2500 usually

Unfortunately, it may be on "borrowed time".





If it wasn't worked too hard and pushed constantly it may surprise you and last a good while yet, or, the first time it gets enough fuel to pull 3000 rpms it may just spit its guts out.





That would be my luck , wishing you better.

 

[Don Tanklage]

pretty much all i do is tow with this truck



so on the flat stuff it was not worked very hard



but on the grades it is a different story



parts finally get here tomorrow and complete fuel sys rebuild starts then



then, i am taking it on another 2k m trip



good pump or bad



so, if it acts up on that trip, i will know where the prob is, and will send the pump out when i get back



will let you know



thanks again



don