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Discussion Starter · #1 ·
Haven't been able to find any information here regarding these pumps.

My 97 stock 12v has a hard time starting in the summer running a back diesel/gas blend and the factory mechanical lift pump. I've been doing this a long time and changing the blend isn't the answer here when it's a 117 degrees.

These pumps have a >18000 hour duty life and are made for diesel however rated at 13PSI. with 60gph.

Anyone have firsthand experience?

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If your replacing your Factory LP with that electric pump then that pump doesn't put out enough fuel pressure.

How much pressure is your Factory LP putting out? It could be such a thing as the OFV is bad and most will get a adjustable OFV.

Have you checked the prefilter on the engine? If it's restricting fuel flow it can cause fuel problems.
 

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Discussion Starter · #3 ·
I have 15-18lbs. @ idle hot. [email protected] full throttle hot. I have fought this for years only with the black diesel in the summer, the factory lift pump does not like the gas. Thus looking for a.low coat alternative, absolutely not in with Fass or air dog, no thanks.
 

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You could use that walbro pump as a booster pump feeding its 13 psi of pressure into the suction of the stock lift pump. If you make a manual bypass for it (all you'd need is two manual valves), then you could take the electric booster pump out when not running black diesel in 117 F weather ( or should the electric pump fail, you could still get home)
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Discussion Starter · #5 ·
That's exactly what I'm thinking. I can see putting the Walbro pump on the frame rail near the tank or even midship.

I assume running a bypass line that would basically "go around" this pump when or if it failed is what you mean?
 

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Something like the crude drawing below. Just open whichever valve for what you're using and shut the other.

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I have 15-18lbs. @ idle hot. [email protected] full throttle hot. I have fought this for years only with the black diesel in the summer, the factory lift pump does not like the gas. Thus looking for a.low coat alternative, absolutely not in with Fass or air dog, no thanks.
Feel like 15 psi is real low for idle and could be contributing to your starting problems. Put a clamp/vise-grips on the return line for a bit and see if that goes up, if so, replace OFV, if not, try prefilter or check for suction leaks.

The stock LP is a simple positive-displacement design and it will move X cc's per stroke (every other rev as the cam spins) of winter diesel, summer diesel, or kool-aid, it doesn't care. LP is almost certainly not the cause of the low pressure (Assuming it's not 300k miles old with worn-out seals anyway).
 

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With the stock lift pump and stock OFV, my truck ran at 10 psi of fuel pressure just fine for the first year I owned the truck.
Started fine and ran fine, truck wasn’t fast by any stretch of the imagination , no stock 12 valve is, they’re all dog slow stock, but no issues really running or starting at 10 psi of fuel.
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Discussion Starter · #9 ·
Cool thanks for that. Pretty much what I'm thinking just need to figure out how to make that into a clean install that's not a snarl of fuel hose and hose clamps.
 

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Discussion Starter · #10 ·
Feel like 15 psi is real low for idle and could be contributing to your starting problems. Put a clamp/vise-grips on the return line for a bit and see if that goes up, if so, replace OFV, if not, try prefilter or check for suction leaks.

The stock LP is a simple positive-displacement design and it will move X cc's per stroke (every other rev as the cam spins) of winter diesel, summer diesel, or kool-aid, it doesn't care. LP is almost certainly not the cause of the low pressure (Assuming it's not 300k miles old with worn-out seals anyway).
It's not fuel pressure or leak or OFV. It's the black diesel, I can run straight diesel and everything is fine, black diesel with a lot of gas in it the pump goes dry after a hot shut down (zero fuel pressuer cranking) again on straight diesel problem does not exist.
 

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It's not fuel pressure or leak or OFV. It's the black diesel, I can run straight diesel and everything is fine, black diesel with a lot of gas in it the pump goes dry after a hot shut down (zero fuel pressuer cranking) again on straight diesel problem does not exist.
Assuming that is the problem, I guess I just don't see how adding an additional electric pump will fix it?
 

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You could put a one way valve like the foot valve on a well to stop bleed back between the pump and tank. Also change the spring on your lp to increase pressure as well as an adjustable ofv
 

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Assuming that is the problem, I guess I just don't see how adding an additional electric pump will fix it?
Because the gasoline in his "black diesel" is flashing to vapor (often called vapor lock on old carbureted cars). Went you put a fluid under pressure it raises the temp required to flash it to a vapor (hence the reason vapor lock isn't an issue in modern EFI gasoline cars).

So if he were to add the electric booster pump it'd raise the pressure on the "black diesel" such that it no longer flashed, then his issue would go away.
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Discussion Starter · #14 ·
Assuming that is the problem, I guess I just don't see how adding an additional electric pump will fix it?
Using it as a booster pump to get fuel to the factory lift pump is the idea.

I'm not that keen on the idea as it doesn't seem right no necessary, however I've fought this same issue every summer for nine years and sick of it. I'm not sure how it would act when actually in operation?
 

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So if he were to add the electric booster pump it'd raise the pressure on the "black diesel" such that it no longer flashed, then his issue would go away.
Still am not seeing how it changes things. The "booster" pump is (presumably) not always running with the key off, so nothing changes when the truck is off and pressure bleeds off. I guess if you turn the key on and wait a second, it will pressurize the few feet of fuel line between the electric pump and the LP (though not between the LP and the IP -- I don't believe the LP will allow flow through). Is this the point? I don't feel like that will change things much. If there's vapor in the system up in the IP, running an electric pump for a few seconds will do nothing different than cranking the starter (running the stock LP) for a few seconds.
 

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Jim, yes , you’d need to wait a second for electric pump to build pressure, but in a diesel you have a wait-to-start light anyway, so no big deal there.

A hard start ( letting the lift pump turn over a few revolutions) is what the OP is trying to solve. So yes, eventually after a few revolutions the stock lift pump will pick up.

Raising the pressure of a liquid also raising its boiling point or vapor pressure, so it keeps the gases in solution.

The basic engineering concept of the drawing I made above is not new by a long shot, that same idea is in all sorts of stuff in various industries and has been for over a century at least.
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Jim, yes , you’d need to wait a second for electric pump to build pressure, but in a diesel you have a wait-to-start light anyway, so no big deal there.

A hard start ( letting the lift pump turn over a few revolutions) is what the OP is trying to solve. So yes, eventually after a few revolutions the stock lift pump will pick up.

Raising the pressure of a liquid also raising its boiling point or vapor pressure, so it keeps the gases in solution.

The basic engineering concept of the drawing I made above is not new by a long shot, that same idea is in all sorts of stuff in various industries and has been for over a century at least.
I think this would make sense IF the LP was an impeller-style pump or something that allowed fuel through when it wasn't running... but I'm 90% sure that the LP will block fuel flow/pressure. So if you've got vapor in the IP/injector lines/wherever it is... it will still be there after the electric pump fires up, because the only thing that pump will pressurize is the length of fuel line between it and the LP. The engine will still be hard to start until the LP moves enough fuel to clear it all out, and having ~13 psi on the intake of the LP instead of 0 won't significantly change how much fuel it moves per stroke.

I don't think an electric pump is a bad idea for this particular case if vapor is indeed the culprit, but I think you're going to want to build pressure in the IP before starting the truck, which I think means the LP needs to actually be bypassed, and that makes the plumbing a bit more complicated if you want to keep the stock LP as well... you'd want to plumb in w/a check valve between the LP and the filter, and that's a hard line. This might actually be a legit case for a normal-HP 12V getting an airdog/FASS setup.
 

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I think this would make sense IF the LP was an impeller-style pump or something that allowed fuel through when it wasn't running... but I'm 90% sure that the LP will block fuel flow/pressure. So if you've got vapor in the IP/injector lines/wherever it is... it will still be there after the electric pump fires up, because the only thing that pump will pressurize is the length of fuel line between it and the LP. The engine will still be hard to start until the LP moves enough fuel to clear it all out, and having ~13 psi on the intake of the LP instead of 0 won't significantly change how much fuel it moves per stroke.

I don't think an electric pump is a bad idea for this particular case if vapor is indeed the culprit, but I think you're going to want to build pressure in the IP before starting the truck, which I think means the LP needs to actually be bypassed, and that makes the plumbing a bit more complicated if you want to keep the stock LP as well... you'd want to plumb in w/a check valve between the LP and the filter, and that's a hard line. This might actually be a legit case for a normal-HP 12V getting an airdog/FASS setup.
I disagree Jim. Pressurizing the line between the fuel tank an lift but would most likely solve the issue without ever touching anything between the lift pump and injection pump.

Like I said earlier, changing the pressure of a fluid changes is boiling point or the temp at which it'll change phase from liquid to vapor and is does that in both directions, i.e., lower the pressure into a vacuum and it'll change phase a lower temperature. Example, steam water desalinization units , or evaporators as they're also called, boil water at about 165 F by drawing a vacuum on the evaporator to about 19 inhg, they do this to save energy and maximum fresh water production. But the principle is the same with any fluid, the AC systems in our houses and cars use this same principle of changing a fluids pressure to change its boiling and condensing temperatures.

When the lift pump is pulling a vacuum on the what, 8-10 foot ling line going from the tank to the lift pump, its most likely causing some gases to come out of solution / flash a little of gasoline in the black diesel mix to vapor (not really an issue if you're just running straight diesel fuel). These gases make the engine harder to start because the lift pump needs to roll over a few time to get enough actual liquid fuel to get the engine going

Since the line between the lift pump and injection pump is what, maybe 18 inches long, and never exposed to a vacuum, its flashing either a lot less or not at all and once the lift pump makes one stroke , that line would be under pressure anyway.

So in conclusion, I would bet a bunch a money that an electric booster pump (mounted as close to the fuel tank as possible) would solve the hard start issue the OP sees when ambient temps are high running his weird fuel concoction. When running straight diesel, you don't need the booster, but it wouldn't hurt anything (other than waste some electricity and cause wear & tear on the booster pump itself).
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