How is tge low pressure piston lift pump lubricated?

[Sutter1stgen]

Just as the title says. I have a lpplp on the side of the block, and was wondering if it could be bypassed? I would hate for it to run dry if it is indeed lubricated by fuel. Ive installed a Carter 18psi/100gph electric. But would like to keep the piston pump for a backup.

[BC847]

The internal components are in fact lubricated with fuel.

[RCCUMMINS89]

You could make a valve opening/closing it from a direct feed line back to your return line, that is of course if you have a large enough return line.

[Sutter1stgen]

Well hell! I've put 200+ miles on it here and there. I need to remove it completely or figure out a return setup. I plan on running a sump or draw straw here soon. I guess u could use the factory suction as a independent return for the lpplp. Thanks guys for your input, hope I didn't ruin the lpplp.

[RCCUMMINS89]

Has it been running completely unhooked? Or just blocked off...meaning there was fuel in it that just couldn't go anywhere?

[Sutter1stgen]

There is some residual fuel still in it, but blocked off. Rc I know you sell a spring to bring the pressure down on a hpplp. Do you think it will keep up with 6x16s, if I run a larger line? I think I remember bc847 doing a test with a regulated hpplp in the past. I believe psi was sucked down pretty low.

[RCCUMMINS89]

Not a clue if it will keep up with 6x16s.... Depends on how it fuels. What I mean is, when I delete my afc I can drop it down with my setup to like 3 pounds....at 1200rpms. Meaning rpms have allot to do with the fuel pressure in a mechanical pump as well. My pump gives me a minimum of 10 psi at wot above 2000 rpms.

Can always pm me and we can work out a trial, if you are interested. I'd be curious to know as well.....as my pumps haven't been tested on anything with what I consider big injectors.

[Sutter1stgen]

Will do later this evening. Thanks.

[AHineman]

I didn't have a fuel pressure gauge when I was running a low pressure piston lift pump. So I can't tell you the psi it would hold, but it would not keep up. So much so that the truck would run rough and sputter if you ran it too hard. This was with stock lines, a good running pump I had tweaked, and the 6x.016s I still run. Bigger lines may have helped some, but IDK. My old pump died before I ran any, and I wasn't going to take any chances with my new pump.

[Sutter1stgen]

Thank you. Now I'm really caught in the middle. I'd like to keep it all mechanical. But I may have to keep my Carter 100 gph

[BC847]

Some notes I found regarding my running piston lift-pumps . . . .

With the low pressure piston lift-pump, running PDR "190" injectors with the typically tweaked injection pump, I'm seeing . ..

- Approximately 12psig while free-revving the engine to 2500rpm.
- Approximately 9psig at idle.
- Approximately 7psig under WOT.



With the high pressure piston lift-pump, bypass regulator set @ 15psig, PDR "190" injectors, etc . . .

- Approximately 15psig while free-revving the engine to 2500rpm (the FP regulator is limiting it).
- Approximately 13psig at idle.
- Approximately 14psig under WOT.

[PToombs]

Larger lines make a big difference also. I gained 3 psi at idle going from stock to a 1/2" id line and a draw straw. Everything from the lpplp to the IP is still stock. I can't remember how much I gained at WOT, I think it was a couple psi.

[Sutter1stgen]

I wonder how a regulated high pressure piston pump with 1/2" line would handle 6x16s?

And thank you guys for your input

[RCCUMMINS89]

But also... what kind of fp are you getting with that electric? Reason I ask is, I have a buddy who is running 5x14s... making about 340hp, and he can pull it down to about 3 psi with your exact same pump.

[Sutter1stgen]

I don't have a fuel pressure guage yet. But I plan on it. Like AHineman said," he could feel the engine run rough after a hard run. Mine doran do it every pass. But here and there is enough to try another setup, or improve the one I got.