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Lift Pump pressure?

countryboy69

countryboy69

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Marengo,IN
Whats an ideal pressure for a lift pump to the DS4? For a fairly modded 6.5. I was thinking of doing something different than a stock style pump

Has anyone tried this? I searched but found nothing.

Maybe a higher pressure pump with a regulator?

Lets hear what ya got!!!
 
Ideally, you always want to have at least 6psi, even at WOT to maintain the most power and keep the IP happiest. I would not put in more than 14psi at the IP though, as it might start affecting housing pressures and cold idle and advance.

A lot of people have a higher powered LP, it can be quite a difference maker when running more than stock fueling. The Walbro FRC-10 is convenient and not too pricey. Otherwise there is a cheap Airtex unit identical to stock but with a pressure spec of 14psi, but dont know how long it will last. The there is the plethora of other aftermarket units that can get into the $300+ area.
 
Curious, the DS4, isn't it totally electronically controlled, advance and all?

For sure, pressures over 6 will mess with a DB2 adv... The key is Volume.
 
3500GMC said:
Curious, the DS4, isn't it totally electronically controlled, advance and all?

For sure, pressures over 6 will mess with a DB2 adv... The key is Volume.
Click to expand...

It is electronically controlled, but you still shouldnt be overloading the transfer pump with high pressure and not allow the relief valve to function correctly. And its possible to overcome the strength of the stepper motor, and not code for it because you have to 5 degrees off before it codes. The pressure mapping of the IP for fuel metering is assuming an input pressure of 6-9psi to the transfer pump, then it multiplies that based on RPM from 30-130psi.
 
Pressure is like voltage. Flow is like amps.
You could have 100 PSI and little flow. Like a 9 volt battery trying to spin the starter. Not enough amps/flow. 9 volts goes to 0 volts when it hits the starter... Engine RPM goes up and the IP returns more fuel to the tank and uses more fuel. Thus 17 PSI at idle can go to a vacuum at WOT full RPM because there isn't enough flow. Snaps of the throttle also drop pressure from sudden fuel demand - it takes a moment to get the heavy fuel moving.

You get more flow from the higher pressure Walbro over stock. You get ~50 GPH from the Walbro. Put two in parallel to get 100 GPH at the same pressure - this requires "t" fittings. Or get a higher GPH pump. 100 GPH is enough to keep up when using biodiesel and 250 GPH (overkill) will keep 10 PSI at the water drain. (My IP has some changes that may flow more fuel through it than stock.)

The filter restricts flow and has a pressure drop.

You want flow on fail for the pump via a bypass check valve or pump design. Or you stop just like a gas engine when the (lift)fuel pump quits.
 
War Wagon I agree totally with what your saying because I have a setup on the Alky race car that kinda follows this thinking. I am running a bypass system

My fuel pump on the block pushes a heavy and full 14 psi. It goes from there to a fuel log with 2 lines to the float bowls on the carb. Out the end of the log it goes to a bypass valve that is hooked to throttle linkage, from there it goes to a regulator and then back to the fuel cell. The regulator is set to the lowest pressure I want(7psi) at any given time. Thats idle so the high 14 psi doesnt blow the needle and seats. As the throttle opens the bypass valve closes bringing my pressure at the log up to 11 psi.

I wonder if a log setup and even a regulator running with dual pumps as you mentioned would be a nice setup? I do run Biofuel as I make mine from used cooking oil.
 
Thanks for the links Burning Oil and I sent some customers your way last week. Guy from Indiana getting a 4" for a 4 door. I will be putting that on!

He will be hunting more stuff as we build his too.
 
I noticed on the page for the Walbro pump that under high loads the pressure could drop to zero or even negative? Is that still heating up the PMD or is that only if its still on the pump?
 
d Play" for GMT-400 trucks or 88-2000 Chevy GMC. The stock lift pump only puts out 5PSI and can drop to 0 or negative on hard acceleration or driving up hills and mountains.

The add for the Walbro^^^

Oh and I am gonna have to get the bigger inlet for the IP! I figure since I am finishing the truck with new fuel lines and all the changes I had better address all I can.
 
countryboy69 said:
d Play" for GMT-400 trucks or 88-2000 Chevy GMC. The stock lift pump only puts out 5PSI and can drop to 0 or negative on hard acceleration or driving up hills and mountains.

The add for the Walbro^^^
OK, thats for a "stock" oem type pump not a Walbro.

Oh and I am gonna have to get the bigger inlet for the IP! I figure since I am finishing the truck with new fuel lines and all the changes I had better address all I can.

Not required, but suggested by most.
Click to expand...
.
 
countryboy69, I would suggest a stock style airtex pump if you are staying with the stock fuel lines and no-prefilter. The pressures I was seeing with my healthy stock pump were more than enough for a stock truck.

But if you are going for possibly a computer chip or reflash, I would highly reccomend the FRC-10 from leroy with a pre-filter. You will not be dissapointed with the pressures.
IMG_0925.jpg

-Nick
 
countryboy69 said:
I noticed on the page for the Walbro pump that under high loads the pressure could drop to zero or even negative? Is that still heating up the PMD or is that only if its still on the pump?
Click to expand...
Having positive pressure at all RPM's and loads keeps the IP cool and healthy,never mind were the PMD is located.
Starving the IP by running negative fuel pressure hastens its demise.
 
Already have a chip tune and doing race car style AN lines. Along with a pre-filter. That what got me wondering what I could do different for a pump. Have a lot of other stuff going on with this motor too and trying to get the most from it. Wish I had knew about the new cam from heath before we buttoned it up last week!
 
buddy said:
.....The pressure mapping of the IP for fuel metering is assuming an input pressure of 6-9psi to the transfer pump, then it multiplies that based on RPM from 30-130psi.
Click to expand...
Ah hah. :pat: That answers a nagging question I have had. So when the PSI at the IP inlet goes below 6 you are out of the hard coded assumptions the PCM (ECM) is making about filling times and such.
 
L98TPI said:
Ah hah. :pat: That answers a nagging question I have had. So when the PSI at the IP inlet goes below 6 you are out of the hard coded assumptions the PCM (ECM) is making about filling times and such.
Click to expand...

Its more like below 1 psi that problems might develop,most stock pumps have a hard time keeping 3 PSI just cruising
 
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