Argh!!! Fuel pressure issues....
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Argh!!! Fuel pressure issues....

  1. #1
    Half a bubble off jrork's Avatar
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    Default Argh!!! Fuel pressure issues....

    Okay, I’ll admit it, I’m stumped and need some fresh minds!

    My son and I have thrown his boat together with a bunch of spare parts I had in the shop and we're struggling with fuel pressure issues.

    The motor is a mild 468” Chevy. The fuel system comprises of twin SS gunnel tanks.
    The tanks are vented with separate vent lines and vented caps.
    Coming out of the tanks are 2 3/8” NPT 90s with 3/8” hose barb out of the top of the tanks. I know, not ideal but this was a 4 week thrash to get it together.
    From the tanks we have about 2 1/2' of 3/8” rubber fuel line to a tee.
    Off the tee is -8 SS to a Holley HP150 electric pump that is mounted as low in the keel as possible and well below the tank bottoms.
    From the pump we ran -8 to a standard Holley regulator.
    From the regulator we ran -8 to the carb with an inline fuel pressure gauge.
    Carb is a 1407 Edelbrock

    This setup worked flawlessly for his maiden voyage and then again on the Friday of the Laborday weekend.
    That Friday afternoon he ran the heck out of the boat to the point that he ran the boat out of gas.

    We dumped some more gas in it and it got fuel pressure right away but it’s never been right since.

    It’s gotten to the point that it won’t even allow the boat to get up much past 3000 rpm in the water with little to no fuel pressure.

    We loaded it up and brought it home and we’ve been messing with it ever since.

    The fuel pressure on the inline gauge up near the carb jumps all over the place. It’ll go 9lbs then 3lbs then 6lbs then 2lbs. It’s completely inconsistent.

    *I’ve changed the fuel filters.
    *Swapped out the regulator with a spare Holley regulator I had in the shop.
    *Bypassed the relay (momentarily) to make sure the pump was getting sufficient voltage.
    *Opened up the fill caps so I know it’s got enough venting.
    *Pulled the pump apart and cleaned the inlet screen.

    Still inconsistent and insufficient fuel pressure hovering around 3lbs but continues to bounce all over the place. I could probably turn the key right now and it’d show 9lbs for a second and then drop soon after to 3lbs.

    One of our friends (thanks Glenn) mentioned that that the rubber hose might be culprit and so I disconnected the fuel line from the tee and put it in a coffee can of fuel and turned the key. The fuel pressure was 7.5 lbs and stayed consistent.

    Figuring that I must indeed be collapsing the fuel hose, I replaced the little bit of rubber hose with new Goodyear 3/8” fuel line and put it all back together.

    Nuthin, still does it. Seems to hang around 2 to 3lbs of fuel pressure but still jumps around.

    So here I am, completely stumped and hoping that you guys can give me some ideas.

    If it was the fuel pump taking a dump, I would have expected it to be consistently low and plunking the line in a coffee can of fuel shouldn’t have changed anything.

    If the pickup tubes were too small, that should have shown that right away, not till after he ran it out of gas while boating.

    Does anybody have any ideas or see something I’m missing?

    Thanks………john
    Last edited by jrork; 09-20-2009 at 04:26 PM.

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  3. #2
    21 Daytona Outlaw's Avatar
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    John, two things I can think of, the screen on the bottom of the pickup tube and the screen on the inlet side of the fuel pump. Maybe they picked some trash
    when you ran it low on fuel. Just a thought
    #55

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    tintingsandiego krusn56's Avatar
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    I ran into a fuel pressure problem when I first got my boat. I took a gas tank(plastic can) with and ran a line into it. I had fuel pressure that way. I started cleaning out the tank in the boat and it had debris in it. Every time I would stomp on it the debris would get sucked up at the intake of the tank. Took a while to get it all out and kept changing filters for a couple trips but it was fixed. How long had the boat sat before you used it. Tanks could of had some trash in it. Fresh fuel and some wakes could of made the debris come loose. Look into cleaning out your tanks.....
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  6. #4
    Senior Member Rain Maker MN's Avatar
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    Try only drawing from one tank at a time....a 3 way valve

  7. #5
    Senior Member fleetimus's Avatar
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    Debris in tanks. Identical symptoms and found this in tanks!!!!!!!


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    Senior Member GAWnCA's Avatar
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    I wonder if you back blow the lines fro the carb and then from the splits if you can clear some of the garbage out that way? Also, are the fuel filters dirty? Could have dirt in the pressure regulator. And if it got past that there's a small screen filter in the carb, or there is in mine. Lotas of places for crud to collect and cause trouble. Good luck!
    Wags

  9. #7
    senior member turbo wog's Avatar
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    Quote Originally Posted by jrork View Post
    Okay, I’ll admit it, I’m stumped and need some fresh minds!

    My son and I have thrown his boat together with a bunch of spare parts I had in the shop and we're struggling with fuel pressure issues.

    The motor is a mild 468” Chevy. The fuel system comprises of twin SS gunnel tanks.
    The tanks are vented with separate vent lines and vented caps.
    Coming out of the tanks are 2 3/8” NPT 90s with 3/8” hose barb out of the top of the tanks. I know, not ideal but this was a 4 week thrash to get it together.
    From the tanks we have about 2 1/2' of 3/8” rubber fuel line to a tee.
    Off the tee is -8 SS to a Holley HP150 electric pump that is mounted as low in the keel as possible and well below the tank bottoms.
    From the pump we ran -8 to a standard Holley regulator.
    From the regulator we ran -8 to the carb with an inline fuel pressure gauge.
    Carb is a 1407 Edelbrock

    This setup worked flawlessly for his maiden voyage and then again on the Friday of the Laborday weekend.
    That Friday afternoon he ran the heck out of the boat to the point that he ran the boat out of gas.

    We dumped some more gas in it and it got fuel pressure right away but it’s never been right since.

    It’s gotten to the point that it won’t even allow the boat to get up much past 3000 rpm in the water with little to no fuel pressure.

    We loaded it up and brought it home and we’ve been messing with it ever since.

    The fuel pressure on the inline gauge up near the carb jumps all over the place. It’ll go 9lbs then 3lbs then 6lbs then 2lbs. It’s completely inconsistent.

    *I’ve changed the fuel filters.
    *Swapped out the regulator with a spare Holley regulator I had in the shop.
    *Bypassed the relay (momentarily) to make sure the pump was getting sufficient voltage.
    *Opened up the fill caps so I know it’s got enough venting.
    *Pulled the pump apart and cleaned the inlet screen.

    Still inconsistent and insufficient fuel pressure hovering around 3lbs but continues to bounce all over the place. I could probably turn the key right now and it’d show 9lbs for a second and then drop soon after to 3lbs.

    One of our friends (thanks Glenn) mentioned that that the rubber hose might be culprit and so I disconnected the fuel line from the tee and put it in a coffee can of fuel and turned the key. The fuel pressure was 7.5 lbs and stayed consistent.

    Figuring that I must indeed be collapsing the fuel hose, I replaced the little bit of rubber hose with new Goodyear 3/8” fuel line and put it all back together.

    Nuthin, still does it. Seems to hang around 2 to 3lbs of fuel pressure but still jumps around.

    So here I am, completely stumped and hoping that you guys can give me some ideas.

    If it was the fuel pump taking a dump, I would have expected it to be consistently low and plunking the line in a coffee can of fuel shouldn’t have changed anything.

    If the pickup tubes were too small, that should have shown that right away, not till after he ran it out of gas while boating.

    Does anybody have any ideas or see something I’m missing?

    Thanks………john
    jimthetoolman had the same problem & it was his other tank sucking air. his pickup tube fell out & he had 3lbs of fuel pressure! are both tanks full?

  10. #8
    Senior Member Hass828's Avatar
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    That pump has a bypass with a spring I believe, may have some trash in it.
    May be sucking air someplace.

  11. #9
    Senior Member GAWnCA's Avatar
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    Quote Originally Posted by turbo wog View Post
    jimthetoolman had the same problem & it was his other tank sucking air. his pickup tube fell out & he had 3lbs of fuel pressure! are both tanks full?
    Would that also cause the erratic fluctuations in pressure?
    Wags

  12. #10
    Senior Member GAWnCA's Avatar
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    Quote Originally Posted by Hass828 View Post
    That pump has a bypass with a spring I believe, may have some trash in it.
    May be sucking air someplace.
    I was also thinking that maybe the diapham in the fuel pump might have a in hole in it as well.
    Wags

  13. #11
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    Quote Originally Posted by Outlaw View Post
    John, two things I can think of, the screen on the bottom of the pickup tube and the screen on the inlet side of the fuel pump. Maybe they picked some trash
    when you ran it low on fuel. Just a thought
    Quote Originally Posted by fleetimus View Post
    Debris in tanks. Identical symptoms and found this in tanks!!!!!!!

    That makes three of us who had the same problem. As GAW mentioned blow through the line backwards. But from the fuel filter back (where is your filter mounted?) You should have one from each tank or one after the tee. Anyway take an air compressor and blow back from the tee. I'd bet problem gone for a while.

    S CP

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    fast is the other half.
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  14. #12
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    Quote Originally Posted by GAWnCA View Post
    I was also thinking that maybe the diapham in the fuel pump might have a in hole in it as well.
    Holley 150 is an electric pump.....no diaphram.

    S CP

    "Dark Sarcasm"
    Going fast is only half the fun ... what you make go
    fast is the other half.
    " A Government big enough to give you everything you want is big enough to take away everything you have"

  15. #13
    Senior Member GAWnCA's Avatar
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    So how does it pump then? The replacement parts all seem to be the type of a diaphram.
    Wags

  16. #14
    Senior Member Sanger Pete's Avatar
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    I also had the same symptoms and found that the fuel inlet screens were plugged. Finally narrowed it down by running a fuel line from the Tee down the fuel fill--presto, 5000+ rpms.

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