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Need some help low fuel pressure

Discussion in 'The Hokey Ass Message Board' started by Hotrodmyk, Sep 22, 2012.

  1. I have a '34 Ford pickup with a 327, mild Comp cam, Edelbrock Performer intake and an Edelbrock 1406 carb. It is plumbed with 3/8 steel tubing from the tank up with a Holley "red" pump mounted below tank level. It is wired on a relay with 10 ga wire. PSI is 7. My problem is that after a short time the pressure gauges shows 0. The truck still runs OK but I'm afraid of lean out problems. The tank is clean.

    The scenario is almost the same as a recent Hot Rod Magazine article where a guy had an old Mr Gasket pump die and replaced it with a new Carter generic pump then his problems started. I had the same pumps. Same situation.

    Can anyone help?
     
  2. Deuces
    Joined: Nov 3, 2009
    Posts: 19,916

    Deuces
    Member
    from Michigan

    Those Holley "red" pumps need a by-pass return line from the regulator back to the tank...
    I have one of those on my o/t '91 Fox car with a Windsor...
     
    Last edited: Sep 22, 2012
  3. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,955

    gas pumper
    Member

    If you have a liquid filled press gauge in the engine compt when it gets hot it no longer reads true pressure. They are only accurate at ambient temps. When they get hot, the pressure in the gauge case goes up because they are not vented to atmosphere. Try an un-dampened gauge before anything else.
     

  4. Actually although a return regulater works real well with them the Rd and the Blue are supposed to be able to run without the return line, the black pump is the one that Holley sughests needs a return line.

    When the rpressure drops check the pump and see if it is hot. If it is then I suspect that a return line is you option. But Holley says that the red pump doesn't need one.

    Here is a deal I ran into on an older holley pump with the same symptoms. It would run fine then the pressure would drop off sometimes enough to kill the engine. I replaced it with a spare that I had on the shelf. I was going to toss it and decided to take it apart. It had a conical inlet screen and I found what appeared to be a label off of something in the screen. Just something to look for.
     

  5. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    It's best to put a filter in the line to prevent debis entering the pump. Much cheaper to change the filter than the pump.

    Do you have a fuel pressure gauge mounted in the vehicle or how did you notice a pressure drop? You might want to put some type of return near the carburetor to allow fuel to circulate to keep the pump cool. You probably only need 6 psi.
     
  6. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    I am not familiar with Holleys red pump, but your line is way to small.

    I run 3/4 to the pump, 1/2 to the front regulator, then 3/8s to the carb on any performance engine.

    I put the filter right before the pump, and in winter storage run Marvel Mystery oil through it.

    any length of 3/8s longer then 24 inches, you suffer a big volume loss, and it puts alotta pressure on the pump, thats both sides.

    In race application, I run 3/8s to each float bowl off the reg not longer the 12 inches....

    The issue of no return line, would actually raise feed line psi, unless the pump is cavitating??
     
  7. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    Not all filters are suitable for use with electric fuel pumps. Some will collapse internally from the suction or otherwise restrict the flow. The ones that work are the steel mesh type. If you have one of the fiber ones in there it might be overworking the pump and overheating it.

    Don
     
  8. D.W.
    Joined: Jun 5, 2004
    Posts: 2,070

    D.W.
    Member
    from Austin Tx.

    ^^^What he said.


    Chased this myself once. Remove the rubber plug from the gauge & dump out the glycerin. Reinstall the gauge & see what it reads when hot.
     
  9. Deuces
    Joined: Nov 3, 2009
    Posts: 19,916

    Deuces
    Member
    from Michigan


    Correction: I just went and looked under my pony... It's the Holley "black" pump I have bolted to the spare tire well..:rolleyes::eek::eek:
    Sorry!..:eek:
     
  10. Deuces,
    The holley pumps are backward in color by my way of thinking. You would think that red would be the race pump. I always have to think about it at least twice and sometimes get out a book to make sure that I didn't get it backward. :eek:

    Good for you to rethink it then admit that the Holley color code got the best of you. :cool:

    Now here is the clinker, I run 3/8 line and a blue pump to feed 400+ ponies of small block and never starve. I did run a 1/2" line on a big mopar once in a class where stock fuel pump was required. It was starving on the big end and we used the 1/2 feed line to over come the problem.

    One of the things that I have noticed when fellas are bulding a car is that they normally go one way or the other, it is over kill on the feed or not enough. I suppose overkill is better than the other.
     
  11. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    I've only heard of that big of line used with alcohol or in race cars where sanctioning bodies limit fuel cell capacity so car builders try to make up for it by having lines that can hold extra fuel. The hole in the seat of the needle valve that lets fuel into the carburetor bowls is probably 3/16 or less. OP has a mild 327 that probably wouldn't need over 5/16 line. The pump is rated at 97 gph, about 1.6 gpm which is easily handled by a 3/8 line.

    When there is little or no flow, the impeller is spinning in the pump, the fuel is circulating through the internal bypass and the fuel might be vaporizing in the pump causing cavitation. Once there is any flow, the incoming fuel is liquid and the pump pressures up again. A 6 psi return line near the carb would keep fuel flowing through the pump.

    Here are Holley's installation instructions.
    http://www.holley.com/data/Products/Technical/199R7914-3rev3.pdf

    Note that the red 7psi pump with the internal bypass is not alcohol compatible. They also say the pump doesn't have much suction.
     
  12. Guys, thanks so much for the help. I have some things to check. Gas Pumper, yes I do have a liquid filled gauge. I will look around and see if I have another one without the liquid. BTW when this happened, I checked the fuel line all the way from the tank up. It was cool to the touch except right at the gauge area but not too hot to touch.
     

  13. If you are cool to the tank you can rule out pump overheating.
     
  14. Where/how do you have that pump mounted?

    If it is not gravity feed that will be part of your problem. The other may be a cheap-ass gauge.

    I run a Holley "Black" pump with no return line and no problems.
     
  15. D.W.
    Joined: Jun 5, 2004
    Posts: 2,070

    D.W.
    Member
    from Austin Tx.


    Like I said. Dump the liquid out.
     
  16. Pump is below tank level mounted inside frame rail far away from exhaust.
     
  17. Well sure as shootin' that fixed it. Thanks so much for your help....AND...saved me a ton of brain cells!
     
  18. johnybsic
    Joined: Oct 8, 2009
    Posts: 612

    johnybsic
    Member
    from las vegas

    dammped gauges dont work well when hot?
    Hmmm. No shit?
    I've been chasing fluxing fuel pressure for a week or so, seems 6-7psi on start-up, but drops to like 3psi when warm, car runs great, floats where they should be.
    I just kept adjusting the regulator. its a holley mech pump by the way.
    Learned something!:eek:

    ill look into this myslef.
     
  19. D.W.
    Joined: Jun 5, 2004
    Posts: 2,070

    D.W.
    Member
    from Austin Tx.

    Glad you got it ironed out. I remember chasing this myself for a couple of weeks. It was maddening haha!
     
  20. Geeneius ^^^^^ !!!! >>>>.
     
  21. YUP, exactly. I could let it sit on fast idle and as the temp came up the pressure fell off. Drove me nuts. This is the place for answers!:D
     
  22. johnybsic
    Joined: Oct 8, 2009
    Posts: 612

    johnybsic
    Member
    from las vegas

    DUDE.

    sure as sh*t solved it issue!
    I was starting to worry about a pump issue or whatnot. Very cool.

    I pulled the gauge off after driving it, the gauge was warm. when first cracked the plug loose it squirted out under pressure. (uh huh)

    emptied it out, reinstalled and shes nice n steady.

    Thanks guys!
     
  23. johnybsic
    Joined: Oct 8, 2009
    Posts: 612

    johnybsic
    Member
    from las vegas

    you think i would have heard about this by now?!?
    I mean most gauges i see at our speed shop are liqud damped. Hmmm

    Milage may vary, But it sure as shit worked for me:D
     
  24. Makes you wonder, doesn't it? You go to buy a gauge and the guy says "you don't want this cheapass dry gauge, how about this cool oil dampened one?" How many are out there chasing ghosts like we were?

    Well, that won't happen again.:mad:
     
  25. 77powerwagon
    Joined: Oct 22, 2010
    Posts: 44

    77powerwagon
    Member

    Yeah I had same issue on an O/T 70 bronco. I was the dampened guage
     

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