100+ PSI fuel pressure

mgeistman · Jun 3, 2012

Twan said:
Think of it like a air compressor, the tank has 150psi, then regulator is set at 100psi for the nail gun. The regulator is there to keep the pressure after it controed, not before. I'm sure that is a 100 psi pump, so it will put out 100psi all the time, as long as it can flow that much.

So if this is true?...... What do you run your return line pressure at to keep 60 psi on the heads? I think your looking at it backwards. To different types of reagulators were talking about here. The type were talking about is regulating pressure before the regulator, the type that would be before a pneumatic tool is regulating the air pressure after it leaves the regulator.

mgeistman · Jun 3, 2012

If the regulator was in front of the heads we would be using the style you're thinking of but since the regulator is after the head you're using a different style it's a total different set up than what you're thinking

Twan · Jun 3, 2012

What stops the pump from pushing it's 100 psi?
I see what your saying, but a small line should keep pressure up. I seen guys with the air dog running them at 65 psi. Maybe his pump is to big, or to regulators?

Twan · Jun 3, 2012

I don't run returns on my big blocks, but that is a good point, would a small return line be able to keep the pressure, or would the best thing to do would be to put another regulator on right after the pump to keep it from pushing full pressure.

mgeistman · Jun 3, 2012

Twan said:
I don't run returns on my big blocks, but that is a good point, would a small return line be able to keep the pressure, or would the best thing to do would be to put another regulator on right after the pump to keep it from pushing full pressure.

well if he put the same size 90's on the back of the heads as the front, and still has the same issue i would say he needs a larger reg. or maybe one after each head, or a reg. after the pump/before the heads.

the reg. he is using doesnt read pressure on the return side, it reads pressure on the inlet the reg. so i dont think the size of return would play a factor in this bc pressure in between the back of the heads and the reg. is working properly, that being said it pretty much narrows it down to the banjos have a pressure drop across them, meaning there acting as a non adjustible regulator, and keeping the regulator he has now from doing its job completly.

mgeistman · Jun 3, 2012

Twan said:
What stops the pump from pushing it's 100 psi?
I see what your saying, but a small line should keep pressure up. I seen guys with the air dog running them at 65 psi. Maybe his pump is to big, or to regulators?

the reg. controlls the pump flow witch controlls pressure. your 100% correct about small line keeping the pressure up ,and thats excatly whats happening here, but instead of it being a line holding back flow its a banjo bolt. make sense?

Twan · Jun 3, 2012

But the pump will push 100psi till it hits the reg right? Can he put a gauge on right before the reg, see if the pressure is at 100psi after the heads and before the reg?

mgeistman · Jun 3, 2012

Twan said:
But the pump will push 100psi till it hits the reg right? Can he put a gauge on right before the reg, see if the pressure is at 100psi after the heads and before the reg?

no the pump will NOT make 100psi before the reg. if flow stays the same from the pump to the reg. unless you have the reg. set at 100psi

mgeistman · Jun 3, 2012

in this case the flow is restricted before the reg. so all he is regulating is the pressure in between the banjo in the rear of the heads and the reg.

windrunner408 · Jun 3, 2012

I have a question, where the pressure readings taken while the truck was running or shut off but with the key on to run the pump??

mgeistman · Jun 3, 2012

At the bottom of the first post he mentioned that the truck was not running. I know what your getting at I think. Do you think fuel consumption at Idle would make that big of a difference? This didn't cross my mind yet. Good point Nate

Twan · Jun 3, 2012

Thanks for explaining, still don't fully understand, can't wait to see what he finds.

mgeistman · Jun 3, 2012

I can keep trying to explain what u don't under stand if you like? Maybe someone can explain it better than me will chim in. Sorry couldn't help more

windrunner408 · Jun 3, 2012

Sorry I missed that. No I didn't think that fuel consumption would be an issue persay, I was just curious.

I have to say that I think this is just gonna be a characteristic of the fuel system that is in place. The pump is gonna find the first restriction and pump up to its full capacity (100psi I guess) and then the pressure down stream of that will always be less. I would be interested to know what the pressure is at the discharge of the pump. I also believe that the biggest restriction is the banjo bolts but the 90* fittings will also have pressure drops. Basically the way I see this system is that (right now anyways) pressure is controlled at one point to be 55psi but up stream is a bunch of restrictions (i.e. banjo bolts, 90* fittings, pipe length, diameter changes, etc.) that is going to cause the supplying pump to have to put out more than 55psi in order to have that pressure after the fuel has traveled through all those obstacles.

mgeistman · Jun 3, 2012

windrunner408 said:
Sorry I missed that. No I didn't think that fuel consumption would be an issue persay, I was just curious.

I have to say that I think this is just gonna be a characteristic of the fuel system that is in place. The pump is gonna find the first restriction and pump up to its full capacity (100psi I guess) and then the pressure down stream of that will always be less. I would be interested to know what the pressure is at the discharge of the pump. I also believe that the biggest restriction is the banjo bolts but the 90* fittings will also have pressure drops. Basically the way I see this system is that (right now anyways) pressure is controlled at one point to be 55psi but up stream is a bunch of restrictions (i.e. banjo bolts, 90* fittings, pipe length, diameter changes, etc.) that is going to cause the supplying pump to have to put out more than 55psi in order to have that pressure after the fuel has traveled through all those obstacles.

:whs:

windrunner408 · Jun 3, 2012

Yea I really think this is just gonna be a characteristic of this pump because there is no pump controller to turn it down with rpm so it is just gonna run at its full capacity when it is powered on. JMO on this.

IdahoF350 · Jun 3, 2012

Fuel systems are NOT like compressed air systems. You're regulating the pressure BEFORE the regulator, not after. If there is a restriction anywhere before the regulator that flows less than the regulator, the pressure before the restriction will always be HIGHER than at the regulator itself. The Banjo assemblies are SEVERELY limiting the fuel flow to the current regulator.

The fix to this is one of several methods:

Fix #1 (cheap fix, not the best fix)
Add a -6AN line from the fuel block to the regulator. This will bypass some fuel past the restriction all the time, still maintaining a constant 55psi in the system.
Pros: Cheap, Easy, Improved Pump Life.
Cons: Flow Characteristics

Fix #2 (more expensive, good fix)
Add a second regulator. Install a multi-port return style regulator off the main feed line in place of your fuel block. Attach the main feed and the head feed hoses on the pressure side of the new regulator. Run the return port to a Y-block on your return line. Attach the return line from the current regulator to the Y as well. Set the new regulator 5psi above the old regulator, this will force fuel to flow through the heads at all times but take the strain off the pump.
Pros: Maintains Full Flow Through Head, Takes Load Off Pump for Pump Life, Will Maintain Lowest Regulated Pressure on System.
Cons: Additional Expense to Update System, Slight Increase in System Complexity.

I've done a lot of fuel systems with big pumps over the years, including regulating A1000s down to 7psi for carburetors. If you just move the location of the current regulator to before the heads you'll starve the injectors under load. If you route the lines from the back of the heads together with the lines from the front of the heads you'll end up with stagnate fuel conditions at idle and low demands that will heat the fuel and negate the full flow properties you want from a regulated return.

FX4 F2-Fifty · Jun 3, 2012

Twan said:
Thanks for explaining, still don't fully understand, can't wait to see what he finds.

To have pressure there must be resistance. In theory,in a regulated return the regulator should be the restriction that determines pressure between the pump and regulator and all excess should go back to the fuel tank.

windrunner408 said:
Sorry I missed that. No I didn't think that fuel consumption would be an issue persay, I was just curious.

I have to say that I think this is just gonna be a characteristic of the fuel system that is in place. The pump is gonna find the first restriction and pump up to its full capacity (100psi I guess) and then the pressure down stream of that will always be less. I would be interested to know what the pressure is at the discharge of the pump. I also believe that the biggest restriction is the banjo bolts but the 90* fittings will also have pressure drops. Basically the way I see this system is that (right now anyways) pressure is controlled at one point to be 55psi but up stream is a bunch of restrictions (i.e. banjo bolts, 90* fittings, pipe length, diameter changes, etc.) that is going to cause the supplying pump to have to put out more than 55psi in order to have that pressure after the fuel has traveled through all those obstacles.

The readings were taken key on, engine off. But i did go drive it with the gauge before the heads and it never budged from 100+psi even at WOT.

This is what i believe is happening as well, when i have the truck apart next week(hopefully) will will remove everything and check them. I will probably drill out the banjos, or possibly order some from Strictly just to be certain. And if the problem still persists, i might have to order 90fittings for the rear of the heads and have new lines made. I hope, but dont believe this will cure the problem 100%. But if i can get the pressure down to around 70psi i will be happy.

IdahoF350 said:
Fuel systems are NOT like compressed air systems. You're regulating the pressure BEFORE the regulator, not after. If there is a restriction anywhere before the regulator that flows less than the regulator, the pressure before the restriction will always be HIGHER than at the regulator itself. The Banjo assemblies are SEVERELY limiting the fuel flow to the current regulator.

The fix to this is one of several methods:

Fix #1 (cheap fix, not the best fix)
Add a -6AN line from the fuel block to the regulator. This will bypass some fuel past the restriction all the time, still maintaining a constant 55psi in the system.
Pros: Cheap, Easy, Improved Pump Life.
Cons: Flow Characteristics

Fix #2 (more expensive, good fix)
Add a second regulator. Install a multi-port return style regulator off the main feed line in place of your fuel block. Attach the main feed and the head feed hoses on the pressure side of the new regulator. Run the return port to a Y-block on your return line. Attach the return line from the current regulator to the Y as well. Set the new regulator 5psi above the old regulator, this will force fuel to flow through the heads at all times but take the strain off the pump.
Pros: Maintains Full Flow Through Head, Takes Load Off Pump for Pump Life, Will Maintain Lowest Regulated Pressure on System.
Cons: Additional Expense to Update System, Slight Increase in System Complexity.

I've done a lot of fuel systems with big pumps over the years, including regulating A1000s down to 7psi for carburetors. If you just move the location of the current regulator to before the heads you'll starve the injectors under load. If you route the lines from the back of the heads together with the lines from the front of the heads you'll end up with stagnate fuel conditions at idle and low demands that will heat the fuel and negate the full flow properties you want from a regulated return.

If all else fails, i will probably be doing this, I will just use the test port on the fuel block and run that to the regulator to bleed off pressure. The 2nd idea is great, but i really dont want to reroute everything and add a second regulator to an already crowded engine compartment.

Another thought: Am i thinking i have a problem when in reality i might not? Has anyone else every checked their fuel pressure before the heads that has the fuel block deleted and a fuel-lab or a1000? Because if one was to just read off the regulator, they would never know and think everything was fine(exactly what i did).

It still amazes me how much useful information there is available on this site. PSA FTW!:rockon::rockon: Thanks everyone for the ideas and explanations!