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busymountain

How much fuel pressure to high pressure pump? Your input helps

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I am getting issue like not enough fuel I believe. How much pressure and volume do I need to supply my 94 high pressure pump? I bought a small electric diesel fuel pump but think it is not enough. I think this pump puts out 7lbs pressure, pretty sure its inadequate. The symptoms are: idles great but getting up to hwy speeds wants to cut out. It has similar symptoms to air in the fuel system. I have heard about FASS, air dog etc.. I want a simple pump that will put plenty of fuel/pressure to my big pump. Whats a good deal for the money? I want to install it in the engine compartment after the fuel filter. I know some of you don't like the idea of after the filter, but do you know any success stories. If installing the pump lower and closer to the tank is my best option for longevity that is fine but would prefer it under the hood. YOUR INPUT WOULD BE GREAT!:)

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The stock lift pump is supposed to put out 17-23psi at idle and should never drop below 25psi when the engine is under a load (driving). Ideally yes they should be over 30, mine runs around 45. I heard 50 is the most you should ever run since above that, you may start blowing o-rings out.

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Thanks for the pump schooling - so you guys suppose I should go with OEM on this one. Have heard alot about folks using the electric aftermarkets but must be for 24 valve?

I will order a new stock OEM and get it going.:doh:

Just for the record it sounds like the OEM pumps are fixable, an "O" ring. Maybe I will tear this one down first before I buy new. This pump has been replace about 3 times last 6 years or so. It could be that the previous owner did not buy oem but aftermarket, then I replaced again. So the stock mechnical supply pumps are better and fixable?

If you guys know of a write up or questions and answers sheet that shows weaknesses and strengths of the 12v and 24v in a condensed version could you direct me to it. It would be nice for us fairly newbies to have a troubleshooting sheet of somekind. I am also currently having trouble with my 03 24v. Only 93 is running.:(

I need these trucks for work so any good direction is appreciated.

--- Update to the previous post...

Just so I am clear on this. You guys like the stock supply pumps for 94 12v. This has the larger pressure pump not the one on previous years. I am sure you have already got that in mind but I want to make certain I am understanding correctly.:)

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Are you sure you have a pump issue and not an overflow valve issue?The mechanical lift pump almost never fails. The overflow valve is what regulates pressure in the P7100, it's a spring loaded ball valve at the exit from the pump to the fuel return line. The older ones look like a stacked banjo setup much as on the top of the fuel filter, you can take out the smaller bolt and stretch or shim the spring and see if your pressure improves.Replacements are well under $50, I got mine on Ebay. I'm still running the stretched spring in the original overflow valve :lmao2:

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Hi ,dont know if you have fixed your problem yet. As you know 30 psi is good for the p pump. sounds like your over flow valve is junk . stock should be around about 22 to 25psi +or -. spring gets tired psi drop and no power :(. Couple of quick fixes there that can work for a while. I would buy the adjustable from Tork Teknology its max is set to 32 psi from factory should bring your pressure from 7 to about 22-25 at idle and max out at about 30+or -. the stock replacements are different from the originals they made the return hole smaller I believe it went from 0.0180 to 0.0120 which increases pressure but doesn't allow for adequate cooling and longevity for pump life.Good luckDave

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thanks for the pump info,i'v owened a01 24v for 7 years  now & i'm still learning about how they work but i also have an 89 that i put a95 Ppump motor in about 2 years ago,just got it back on the road after a year plus frame rebuild.i have a great deal to learn about these systems & love doing so.so far i'v installed #4fuel plate, delivery valves,afc housing forword,star wheel ajusted& boost line blocked off,but i'v been running a holley black pump rated for only 7-10 psi so i may be starving my Ppump when on the go pedel.a must now to stock lift pump fixed. thanks again.

--- Update to the previous post...

thanks for the pump info,i'v owened a01 24v for 7 years  now & i'm still learning about how they work but i also have an 89 that i put a95 Ppump motor in about 2 years ago,just got it back on the road after a year plus frame rebuild.i have a great deal to learn about these systems & love doing so.so far i'v installed #4fuel plate, delivery valves,afc housing forword,star wheel ajusted& boost line blocked off,but i'v been running a holley black pump rated for only 7-10 psi so i may be starving my Ppump when on the go pedel.a must now to stock lift pump fixed. thanks again.

--- Update to the previous post...

thanks for the pump info,i'v owened a01 24v for 7 years  now & i'm still learning about how they work but i also have an 89 that i put a95 Ppump motor in about 2 years ago,just got it back on the road after a year plus frame rebuild.i have a great deal to learn about these systems & love doing so.so far i'v installed #4fuel plate, delivery valves,afc housing forword,star wheel ajusted& boost line blocked off,but i'v been running a holley black pump rated for only 7-10 psi so i may be starving my Ppump when on the go pedel.a must now to stock lift pump fixed. thanks again.

--- Update to the previous post...

thanks for the pump info,i'v owened a01 24v for 7 years  now & i'm still learning about how they work but i also have an 89 that i put a95 Ppump motor in about 2 years ago,just got it back on the road after a year plus frame rebuild.i have a great deal to learn about these systems & love doing so.so far i'v installed #4fuel plate, delivery valves,afc housing forword,star wheel ajusted& boost line blocked off,but i'v been running a holley black pump rated for only 7-10 psi so i may be starving my Ppump when on the go pedel.a must now to stock lift pump fixed. thanks again.

--- Update to the previous post...

thanks for the pump info,i'v owened a01 24v for 7 years  now & i'm still learning about how they work but i also have an 89 that i put a95 Ppump motor in about 2 years ago,just got it back on the road after a year plus frame rebuild.i have a great deal to learn about these systems & love doing so.so far i'v installed #4fuel plate, delivery valves,afc housing forword,star wheel ajusted& boost line blocked off,but i'v been running a holley black pump rated for only 7-10 psi so i may be starving my Ppump when on the go pedel.a must now to stock lift pump fixed. thanks again.

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i'v owened a 01 24v for about 7 years now, i'm still learning new things about it thanks to these forums & others more knowlageble than me(which don't take much)i also own an 89 w/a 95 Ppump motor that i just got back on the road after a year plus frame up rebuild.it has bigger delivery valves, #4 fuel , plate,afc housing forward,star wheel ajusted &4in exhaust.i'v been running a holley black elect. fuel pump since the stock lift pump went some time ago.now after reading this post i see i'm very likely starving my inj.pump when on the go pedal.the black holley pump only puts out 7-10 psi.i'll be fixing my stock lift pump ASAP.thanks again for the info.:thumb1:

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The tork tek. OFV020 adjustable is a great remedy for the overflow valve, has the right sized openings for proper fuel pressure and flow to keep P pump cool :cool:. (DONT buy the updated ones that they have out there, they shrunk the inlet hole from .168 to .105, increases your fuel pressure and will shorten the P- PUMPS LIFE!) You need to get the lift pump going ASAP.... or you will just run like everyone does when they have a crappy overflow valve. You will be running out of fuel in higher RPM's, smoking when cold,ect. 7-10 lbs is no good for the P pump......early burn out, costly to repair. One more thing you might want to consider is the stock fuel line will only let your lift pump run at aprox. 64% idle to 35% 2500 RPM. The lift pump is good for 1.51 gal per min, not the .52 GPM they have it running at , to achieve 100% you need to resize your fuel line from tank to lift pump. I did mine to 9/16 ID tank to p pump and eliminated the prefilter and heater all together , raising efficiency of lift pump form 64%-34% to 100 % all the time . This lets the lift pump work easier, and the P-Pump run much cooler! with full fuel to max RPM. ( Dont waste the $$ on the 1/2 " kit they sell , because costs more and wont be running at 100%) .You might think about a BHAF for more air in its a great combo with your MODS!. I have Pics of the project, I will post them soon. Good luck Dave

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