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Old 05-15-2017, 06:49 PM
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Fuel pressure regulator not lowering pressure

Hey guys, ive had this problem I've been messing with for a few days now and I was wondering if anyone had any insight on this.

Basically the motor is a roots supercharged 454, topped with dual 600cfm Holley supercharger carbs, mild performance motor (street/strip).

I decided to re-use the stock fuel tank instead of a cell to keep it stock looking, and put in a new sending unit (Spectra FG91D) that has a 3/8" outlet and a 1/4" return. Regarding the lines I used some hard line to braided converter fittings, and converted the hard lines to -6AN. so the fuel sender outlet is a 3/8" to a -6AN braided hose, to a fuel filter capable of filtering 100 mocrons and flowing 100gph, to a Holley Blue fuel pump that has a maximum pressure of 14PSI. From there its back to a braided -6AN, to a braided to hard line converter fitting, then its a 3/8" hard line all the way to the front.

Up at the front I convert it back to a -6AN line, to another filter, then to my fuel pressure regulator with is a Holley 12-841, which has one inlet, one outlet and one return and has a PSI range of 4.5-9. I also fitted that with a Aeromotive liquid filled fuel pressure gauge. Then from the outlet of that I have a -6AN braided line going up and seperating to both the carbs.

Going back on the return is a -6AN braided line going to the hard line return which is a 1/4" pipe. That runs all the way back to the fuel pump where it converts to a -6AN which connects to the return on the fuel sender.

In case youre wondering why i went half braided and half hard line is that my buddy gave me his hard fuel lines he was using for his El Camino that he ended up not needing (the lines were clear, he kept the ends plugged and i tested them) and I wanted the braided hose look in the places that'd be visible.

Now heres the problem. We first tried starting the car with just the key on so only the fuel pump was running, and we loosened the regulator so it'd be at its lowest setting. The regulator wouldn't lower anywhere past 9PSI. After messing with it a bit making sure at the same time it wasnt leaking the carbs, we decided to just start the car and mess with it then. So we got the car to fire up (this was the first time starting the motor too by the way) while my dads buddy messed with the timing and I messed with the regulator. The regulator still wouldn't lower past 9PSI (I think it went to 8 but that was it) and when I turned the adjustment screw the other way it went as high as 12PSI. We left it at 9PSI and continued tinkering with the timing and carb adjustment for a few. Got the motor to steady out but obviously it was surging every few seconds so we didnt leave it running for long.

I assumed the regulator was faulty as I read reviews that others were faulty and wouldn't adjust as well and summit said they'd take care of it. Got the new one, installed it and same issue.

Obviously this is making me question a lot. Is the return line too small? Is the pump too powerful? Its not a Holley black but still this car will see the track and I want to make sure its got proper flow during WOT. Shouldn't it slow down once it starts detecting that backup of pressure anyways? I was going to call Holley but theyre closed at the moment and I figured I'd ask here and see if anyone has any ideas I could try and mess with.

If you have any more questions feel free to ask thanks

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Old 05-15-2017, 09:19 PM
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Are you sure the return on the regulator is the right port?

If so are you adjusting it correctly? Might be a stupid question....seen it happen though.

next I'd take it apart and make sure it's assembled correctly and debris free.
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Old 05-15-2017, 10:36 PM
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Quote:
Originally Posted by johnsongrass1 View Post
Are you sure the return on the regulator is the right port?

If so are you adjusting it correctly? Might be a stupid question....seen it happen though.

next I'd take it apart and make sure it's assembled correctly and debris free.
Yes the return is at the bottom labeled "RET" and the instructions say turning the regulator clockwise increases pressure and counter clockwise decreases pressure. First we tried it almost completely out counter clockwise and then went clockwise when that didn't do anything. Pressure was as low as 8psi and went as high as 12.
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Old 05-16-2017, 03:27 AM
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Verify the gauge is correct.
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Old 05-16-2017, 06:06 AM
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how about taking a 3/8 line direct from the regulator return to a container and see if pressure will adjust lower?
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Old 05-16-2017, 08:40 AM
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Quote:
Originally Posted by stanley9875 View Post
Hey guys, ive had this problem I've been messing with for a few days now and I was wondering if anyone had any insight on this.

Basically the motor is a roots supercharged 454, topped with dual 600cfm Holley supercharger carbs, mild performance motor (street/strip).

I decided to re-use the stock fuel tank instead of a cell to keep it stock looking, and put in a new sending unit (Spectra FG91D) that has a 3/8" outlet and a 1/4" return. Regarding the lines I used some hard line to braided converter fittings, and converted the hard lines to -6AN. so the fuel sender outlet is a 3/8" to a -6AN braided hose, to a fuel filter capable of filtering 100 mocrons and flowing 100gph, to a Holley Blue fuel pump that has a maximum pressure of 14PSI. From there its back to a braided -6AN, to a braided to hard line converter fitting, then its a 3/8" hard line all the way to the front.

Up at the front I convert it back to a -6AN line, to another filter, then to my fuel pressure regulator with is a Holley 12-841, which has one inlet, one outlet and one return and has a PSI range of 4.5-9. I also fitted that with a Aeromotive liquid filled fuel pressure gauge. Then from the outlet of that I have a -6AN braided line going up and seperating to both the carbs.

Going back on the return is a -6AN braided line going to the hard line return which is a 1/4" pipe. That runs all the way back to the fuel pump where it converts to a -6AN which connects to the return on the fuel sender.

In case youre wondering why i went half braided and half hard line is that my buddy gave me his hard fuel lines he was using for his El Camino that he ended up not needing (the lines were clear, he kept the ends plugged and i tested them) and I wanted the braided hose look in the places that'd be visible.

Now heres the problem. We first tried starting the car with just the key on so only the fuel pump was running, and we loosened the regulator so it'd be at its lowest setting. The regulator wouldn't lower anywhere past 9PSI. After messing with it a bit making sure at the same time it wasnt leaking the carbs, we decided to just start the car and mess with it then. So we got the car to fire up (this was the first time starting the motor too by the way) while my dads buddy messed with the timing and I messed with the regulator. The regulator still wouldn't lower past 9PSI (I think it went to 8 but that was it) and when I turned the adjustment screw the other way it went as high as 12PSI. We left it at 9PSI and continued tinkering with the timing and carb adjustment for a few. Got the motor to steady out but obviously it was surging every few seconds so we didnt leave it running for long.

I assumed the regulator was faulty as I read reviews that others were faulty and wouldn't adjust as well and summit said they'd take care of it. Got the new one, installed it and same issue.

Obviously this is making me question a lot. Is the return line too small? Is the pump too powerful? Its not a Holley black but still this car will see the track and I want to make sure its got proper flow during WOT. Shouldn't it slow down once it starts detecting that backup of pressure anyways? I was going to call Holley but theyre closed at the moment and I figured I'd ask here and see if anyone has any ideas I could try and mess with.

If you have any more questions feel free to ask thanks

Regulators don't have unlimited capability they are built with a range they can manage. To find that out it should be in the literature with the regulator, knowing the brand and part number would help us help you.


If the regulators prove to be out side of spec then you could consider that Summit has a quality control problem across a production batch something they need to know and should correct.


Bogie
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Old 05-16-2017, 08:42 AM
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Quote:
Originally Posted by johnsongrass1 View Post
Verify the gauge is correct.
Yea that was also on my mind if somehow the gauge is incorrect


Quote:
Originally Posted by dirt t View Post
how about taking a 3/8 line direct from the regulator return to a container and see if pressure will adjust lower?
I was going to try and test that today before calling Holley, it's a -6AN down to the frame where it connects to the 1/4" line and I'll pop the line off there again and put some 3/8" hose to a bucket or something and try starting the car and see if it lowers. If so then there's the issue
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Old 05-16-2017, 11:25 AM
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Originally Posted by BogiesAnnex1 View Post
Regulators don't have unlimited capability they are built with a range they can manage. To find that out it should be in the literature with the regulator, knowing the brand and part number would help us help you.


If the regulators prove to be out side of spec then you could consider that Summit has a quality control problem across a production batch something they need to know and should correct.


Bogie
I mentioned the regulator is a Holley 12-841, I got through summit. Has a range of 4.5-9 PSI with a single inlet, outlet, and return. This is the second one I got from summit and it's showing the same results as the first. I'm almost 100% certain it's because the return line is too small because the fuel can't go through as fast as the pump is trying to push it. I'll check today or tomorrow and post an update
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Old 05-16-2017, 12:08 PM
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Quote:
Originally Posted by stanley9875 View Post
I mentioned the regulator is a Holley 12-841, I got through summit. Has a range of 4.5-9 PSI with a single inlet, outlet, and return. This is the second one I got from summit and it's showing the same results as the first. I'm almost 100% certain it's because the return line is too small because the fuel can't go through as fast as the pump is trying to push it. I'll check today or tomorrow and post an update

One of the most common mistakes when designing a fuel system is using a return line thatís too small. This results in excessive backpressure, which makes it nearly impossible for the regulator to bleed off enough fuel to keep line pressure in check.
https://www.holley.com/blog/post/sel..._for_your_car/

Last edited by 2001Blazer4x4; 05-16-2017 at 12:26 PM.
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Old 05-16-2017, 12:14 PM
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Quote:
Originally Posted by stanley9875 View Post
I mentioned the regulator is a Holley 12-841, I got through summit. Has a range of 4.5-9 PSI with a single inlet, outlet, and return. This is the second one I got from summit and it's showing the same results as the first. I'm almost 100% certain it's because the return line is too small because the fuel can't go through as fast as the pump is trying to push it. I'll check today or tomorrow and post an update

Is this regulator biased to read manifold (blower pressure)? If it is the pressure could be the result of what manifold pressure the regulator is seeing.


Yes the bypass if too small would boost line pressure, probably at least 5/16 line would be better. But if this is the case the worst excess pressure would be at idle because the pump's output is constant where the engine's consumption varies with throttle position and RPM where at idle it isn't using nearly as much fuel as the pump provides. If the pressure comes down as engine speed is increased then the return is too small or obstructed in some other way. The down side of this test is without actually loading the engine by driving the vehicle or putting it on a dyno the fuel pressure probably won't respond, at least not by much, to just running up the RPMs.



Bogie
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Old 05-16-2017, 01:01 PM
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Quote:
Originally Posted by 2001Blazer4x4 View Post
One of the most common mistakes when designing a fuel system is using a return line that?s too small. This results in excessive backpressure, which makes it nearly impossible for the regulator to bleed off enough fuel to keep line pressure in check.
https://www.holley.com/blog/post/sel..._for_your_car/
Yea that makes sense, when I installed the main hard lines I honestly didn't really think much about the return size, and when I bought the pump same thing I didn't really think about how much fuel it would be returning when it's not using that much at idle.


Quote:
Originally Posted by BogiesAnnex1 View Post
Is this regulator biased to read manifold (blower pressure)? If it is the pressure could be the result of what manifold pressure the regulator is seeing.


Yes the bypass if too small would boost line pressure, probably at least 5/16 line would be better. But if this is the case the worst excess pressure would be at idle because the pump's output is constant where the engine's consumption varies with throttle position and RPM where at idle it isn't using nearly as much fuel as the pump provides. If the pressure comes down as engine speed is increased then the return is too small or obstructed in some other way. The down side of this test is without actually loading the engine by driving the vehicle or putting it on a dyno the fuel pressure probably won't respond, at least not by much, to just running up the RPMs.



Bogie
No the regulator isn't boost referenced, just the carbs for the power valves, ignition box and obviously boost gauge I have manifold vacuum going to... Roots Blowers don't need boost referenced regulators I thought? I thought that was just for blow through systems
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Old 05-16-2017, 05:38 PM
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Quote:
Originally Posted by stanley9875 View Post
Yea that makes sense, when I installed the main hard lines I honestly didn't really think much about the return size, and when I bought the pump same thing I didn't really think about how much fuel it would be returning when it's not using that much at idle.




No the regulator isn't boost referenced, just the carbs for the power valves, ignition box and obviously boost gauge I have manifold vacuum going to... Roots Blowers don't need boost referenced regulators I thought? I thought that was just for blow through systems

'No' is the answer I was hoping for. That eliminates one possibility.


This could be the return is too small or something else like a filter on the return or even the nipple back to the tank being only a quarter inch is just too small at idle when looking at how much fuel is delivered to how much has to be returned because of the low consumption by the engine against the constant high output of the pump which might be totally suitable once the engine is burning more fuel when the mains kick in.


Another trick is to use a regular regulator between the bypass and the carbs. This will let the bypass do its thing all the time but should also hold a steady 6 psi at the carbs regardless of engine demand.


Bogie
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Old 05-16-2017, 09:58 PM
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Yup problem was return line size. Used a 3/8" NPT to barb fitting I had lying around on the return port on the regulator, put some 3/8" rubber hose on the barb and put the end into a gas can and unscrewed the regulator and turned the key on and low and behold the pump dropped to about 3-4psi. Adjusted it to about 5/5 1/2PSI and left it for now. That was stupid on my part I should've caught it. So now to order more -6AN braided hose and drop the tank to get to the sending unit and pop in a new unit that has bigger tubes... Luckily there's like 3 gallons of gas in it. Fine tune the car later once the new lines are installed. Thanks a lot for the help guys as always
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Old 05-16-2017, 09:58 PM
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To whoever needs this info:

The Holley 12-841 fuel pressure regulator is Comparable and interchangeable with popular Holley 12-803BP regulator!! Holley also has a NOTE of warning

NOTE: These regulators are designed to work with a single carburetor installation. If two carburetors are used then two regulators will be required, one for each carburetor. Also, two of the P/N 12-803 or 841 regulators MUST be used when running a VOLUMAX fuel pump - one for each fuel bowl on a single holley 4v carb set up !!

The restriction in these regulators is about 1/4 inch "Both regulators feature a 3/8" NPT inlet port and two 3/8" NPT outlet ports with a .220" restriction (7/32")" at the regulators internal port junction!!

Most performance dual quad set ups use one regulator per carb but if hp is high and drag race only full throttle blasts then it may require one regulator per bowl !!
On a single quad drag car it needs one regulator per bowl !

Most regulators have the same drawback and thats were the regulator controls the fuel flow, it narrows down to about 1/4 inch so even if you run 3/8 or 1/2 inch lines its still feeding through this 1/4 inch restrictive point !

Anyone who has ever tore down a regulator for preventive maintenance and inspection knows this fact! And any racer worth his salt knows these facts!!

The better set up for multi carbs is the #12-706-1 VOLUMAX pump and the #12-707 regulator which has 6 outlet ports and has a much bigger .437" (7/16") restriction point ! And can deliver much needed fuel in volume needed for multi carb systems!

For mediocre street performance and to show off a little on the street many people run the restrictive regulators (they don't know any better no fault of their own) But Racers and speed enthusiasts know that they do not work well !!

Anyone can take this with a grain of salt it doesn't bother me if some disagree with me !! I only post this to help those who want to learn

Jester

Last edited by painted jester; 05-16-2017 at 10:07 PM.
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Old 05-17-2017, 07:49 AM
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On top of that lower set pressure opens the regulator so go as low as you can and still feed the bowls.

Pressure is a function of restriction and doesn't always equate to flow so in the case of the dead head type regulators lower pressure has the ability to flow more. ANY amount of pressure is an indication of more flow than what's actually needed so go as low as you can to get the max flow through the restriction. 3 or 4 psi is enough as long as it's hols that, or at least more than 2 at max flow or WOT.
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