Fuel Pressure Question

[maverick350]

When I first put my truck together, I put a low pressure electric fuel pump in line on the frame rail along with the mechanical pump. using the electric for priming purposes for the most part.
I recently replaced the mechanical with a faucet dura-lift, and put in a fuel pressure gauge.

Now here's where it gets interesting. With the small electric pump on the frame rail, maybe 1.5 psi. the 0-30 psi gauge barely twitched.

Turning on the dura-lift on the fender well, 7 psi.

Turning both pumps on, 10 psi.

Turning the engine on with just the dura lift, pressure drops to 4psi.

Under a load, climbing a hill, pressure drops to zero. Truck runs great.

I need to check my gauge with another to be sure, but I'm surprised to see this much of a pressure variation. Is this normal?

 

[OLDBULL8]

Is this the pump you have? 40285
If your sucking clean from the rear tank, that's a long ways (15-20 Ft), specs say 10 Ft.
As long as the truck runs great, whats the problem, put a cover over the gauge and forget about it.

http://www.facet-purolator.com/dura-lift-pumps.php

 

[maverick350]

That's the pump I bought.

I'm just curious if the drop in pressure under a load is normal?

My concern is any long term effects low pressure might have on the injector pump.

 

[IDIoit]

you wont see any "pressure" in the gauge when your flatfooted, because the pump is sucking it all.

you may even gain performance by adding a bigger pump, but at idle mayb e it could pop a seal?
at idle i see 9 psi, at WOT, the pump sucks it like a 2 dollar crack ***** when your holding a franklin over her head.(or so ive heard)
too graphic?

 

[maverick350]

Sounds like you're seeing pretty much the same thing on your pressure gauge as what I'm seeing. Good enough!

 

[fsmyth]

I added an electric 5-lb pump mounted close to the transfer switch, and plumbed it in-line with the valve output.
With an in-line filter into the pump. Consistant 6 PSI. The mechanical pump alone was 5 PSI. Both together is 6.5.
Constant. Loaded or not. Pressure gauge teed off the stock filter housing output.
As a side note, the mechanical pump pulls through the electric pump, so I leave it off except for priming. Works fine.

 

[IDIoit]

FYI, Mel at Conestoga Diesel, calibrates his pumps @ 5 psi.

 

[marmot]

FYI, Mel at Conestoga Diesel, calibrates his pumps @ 5 psi.

40285 has a 4-7psi range
40222/223 is 9-11psi

Both pumps flow 33gph so the difference must be the pressure switch.

Oldbull, spec of 10ft is self priming at 10ft of lift or as some folks, particularly californians holding benjamins call it "head"

 

[laserjock]

Fwiw, I picked up the 40222. It's on the high end of the supply range but I figure by the time it goes through the filter and pulls from the rear tank, the pressure should be on the high side of acceptable do maybe it won't go clear to 0 at wot. Also gives me a little head space if I add another filter.

 

[opusd2]

I have the 40222, and with my inline gauge ( I take it as a ball park figure since it's a simple gauge ), a plastic pre-filter before the pump with primary and secondary filters post pump, I manage 7 PSI idling. Approximately, even though that's what the gauge says.

 

[PwrSmoke]

Pressure is resistance to flow. When pressure is high, the engine isn't using all the fuel being supplied. When pressure is low, the engine is using most or all the fuel being supplied. In other words, low pressure does not necessarily indicate low flow.