fuel pressure problem questions
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fuel pressure problem questions

  1. #1
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    Default fuel pressure problem questions

    broke in the new motor on monday and all is well except that I am loosing fuel pressure, this is my setup, from the tank to a earls screen filter(just for any big trash) to a holley marine blue pump then threw a 4" by 6" 30 micron filter to a holley bypass pressure regulator then to the carb and the bypass goes back to the tank.
    I can run this all day and it stays at 6 lbs, but when I run the motor for about 10 min, at 2000 to 2500 rpm I am dropping to about 1.5 to 2 lbs. of pressure and then have to shut it down, am I missing something here, its working good enough for break in but I can't hit the water this way. can you guys give me a bit of help?
    thanks a bunch.
    Adam

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  3. #2
    Living in a cage of fear thatguy's Avatar
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    I have never ran a bypass on a Holley Blue.

    Run basically the same system on the Miller.
    Tanks to a cartridge separator/ filter, Holley Blue, Holley reg w/ 2 outlets to the 660's.
    No return, set a 6# and never varies.

    Do you run a relay switch?
    Tommy
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  4. #3
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    no relay, just a 7.5 amp fuse, but I have no problems with power to the pump, I used a bypass regulator so the pump doesn't have any problems in long no wake rivers. sometimes up north in Michigan you have to run in rivers for about an hour to get to the next lake, I have heard of guys burning there pumps up doing that, and it keeps the pump cool. this is only happening when the motor is running, (shut off it is always at 6 psi)but at 2000 rpm I am just on the cruse circuits, I don't see any fuel going threw the boosters if that matters but I dont see why it would. its a 850 holley dp carb, the floats are set so when I pull the bowl plugs it just tries to dribble out a tiny bit on the bottom of the threads, and that is how I have always set my floats. I am new to the electric pumps tho.

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  6. #4
    SR
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    Quote Originally Posted by thatguy View Post
    I have never ran a bypass on a Holley Blue.


    Do you run a relay switch?
    Me neither.....I would try blocking the bypass and also wire in a relay............ A single holley 670 on a sbc w/reg. no bypass fed by a blue pump I have,the pressure drops at w.o.t (top feed tanks)....Ya might try a black pump...

    P.S....I might be wrong,but,your pump should run cool (more volume)at cruise speeds,bypass would keep the pump from fighting at idle...
    Last edited by SR; 08-25-2010 at 07:07 PM.

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    Return fuel systems at time show lower pressure, the system lets the fuel flow instead of building high pressure. Unless the engine shuts down then there is a problem. I use a mechanical pump and electrical constant pump.
    Maybe your pump can't supply the amount of fuel needed.

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    just got off the phone with jegs tech, he said it is probably my liquid filled pressure guage and I should dump the fluid out.he said liquid guages are notorious for giving false readings. any one ever heard of this?
    thanks

  9. #7
    gn7
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    Quote Originally Posted by Adam View Post
    just got off the phone with jegs tech, he said it is probably my liquid filled pressure guage and I should dump the fluid out.he said liquid guages are notorious for giving false readings. any one ever heard of this?
    thanks
    All pressure gauges, reguardless of what they are reading, are nothing more than pressure differential meters. They show the pressure difference between the line hooked to the, and the outside air pressure(atmosheric porssure). On a normal gauge, the case is vent to the out side, and can see the atmosphere pressure. Liquid filled cases are sealed. If the case gets hot, pressure builds in the case and shows a lower reading because it is still comparing the line pressure to the case pressure. they are also effected by altitude. the only way a liquid fill gauge can give accurate reading all the time is if you open the vent hole on the case every time you run the boat. Actually, every time you even start the boat. OK in the morning, false readings in the afternoon. Maybe OK on oil pressure because it only throws the gauge off by a pound or 2. But for a fuel pressure gauge, they suck. BG won't even sell them. Dump the fluid.



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    Wet
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    Tanks not venting?

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    Quote Originally Posted by gn7 View Post
    All pressure gauges, reguardless of what they are reading, are nothing more than pressure differential meters. They show the pressure difference between the line hooked to the, and the outside air pressure(atmosheric porssure). On a normal gauge, the case is vent to the out side, and can see the atmosphere pressure. Liquid filled cases are sealed. If the case gets hot, pressure builds in the case and shows a lower reading because it is still comparing the line pressure to the case pressure. they are also effected by altitude. the only way a liquid fill gauge can give accurate reading all the time is if you open the vent hole on the case every time you run the boat. Actually, every time you even start the boat. OK in the morning, false readings in the afternoon. Maybe OK on oil pressure because it only throws the gauge off by a pound or 2. But for a fuel pressure gauge, they suck. BG won't even sell them. Dump the fluid.
    thanks, I am sure that is the problem now, the guage is only about 2' away from a dry header, within 10 min. its getting very hot. makes alot of sence, and after it cools for a bit its back at 6 psi.

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    Quote Originally Posted by Wet View Post
    Tanks not venting?
    venting great, everything is working great,its the gauge. I will dump the fluid out tonight and I bet it will sit right at 6 psi. thanks for the reply.

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    Sounds like you found the prolblem. For an electric fuel pump, I can't understand why people would use anything other than a Weldon pump.

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    If you are going to stick with the bypass regulator, it wouldn't hurt to put a stiff spring in the internal bypass in the pump. I have been told that the internal bypass can aerate the fuel.

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    Quote Originally Posted by cp562 View Post
    Sounds like you found the prolblem. For an electric fuel pump, I can't understand why people would use anything other than a Weldon pump.
    Probably because Weldon are super great pump. There pricing isn't exactly realistic though. Its a pump. Not an artificial heart.



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    Last edited by gn7; 08-26-2010 at 12:47 PM.

  16. #14
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    Quote Originally Posted by Adam View Post
    thanks, I am sure that is the problem now, the guage is only about 2' away from a dry header, within 10 min. its getting very hot. makes alot of sence, and after it cools for a bit its back at 6 psi.
    Most have a small venting screw to re-acclimate the gauge. Either leave the screw out. or drill a tiny hole in the bottom of the gauge can.



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