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Hot Rods Fuel pressure fluctuation still

Discussion in 'The Hokey Ass Message Board' started by doctor chip, Jul 16, 2014.

  1. doctor chip
    Joined: Dec 10, 2010
    Posts: 82

    doctor chip
    Member
    from Delevan NY

    I had a thread on this awhile back and got some good advice. My engine is a 351w with Edelbrock dual quads, their recommended cam,heads,intake etc.. I have changed fuel filters, checked voltage, replaced and relocated electric fuel pump lower than tank, checked fuel intake in tank and still having problems with fuel pressure loss especially (but not always)when I get on it. All line is 3/8 steel. This pump is rated 32gph and 4-7psi. Pressure gauge reads between 4 and 5 most of time. The only other thing I can think off is maybe a higher flowing/higher pressure fuel pump with pressure regulator. Im going nuts with this thing. What do you suggest for pump brand, pressure, and flow rate? or am I missing something else?
     
  2. yellow dog
    Joined: Oct 15, 2011
    Posts: 512

    yellow dog
    Member
    from san diego

    I'm reading that your "Pressure gauge reads between 4 and 5 most of time."....which shouldn't be a problem but I assume that it drops unacceptably under demand. You didn't mention that you have established adequate venting, however a 32gph pump isn't overly abundant (only 30% of it makes the car go). Spend a hundred bucks or so and get a Holley red or blue, Aeromotives are great but more money.
     
  3. You know about the liquid filled gauges needing burped to remain accurate as the temperature changes?
     
  4. doctor chip
    Joined: Dec 10, 2010
    Posts: 82

    doctor chip
    Member
    from Delevan NY

    Thanks, ordered the holly red pump - hope that is the fix, getting tired of throwing money at this thing.
     

  5. stimpy
    Joined: Apr 16, 2006
    Posts: 3,546

    stimpy

    and read the mounting instructions on the Holley pump as they can be finicky if mounted wrong . ( as in location and distance and height ) , they are meant to push fuel, not pull it and do not like pulling it and will cavitate . this is the number one problem with complaints on them . the pump mounted too high or too far from the tank .
     
  6. My 2c. The fuel is moving away from the pick up when you get on it.
     
  7. doctor chip
    Joined: Dec 10, 2010
    Posts: 82

    doctor chip
    Member
    from Delevan NY

    the problem will occur sitting in the garage when the second carb opens. As part of my initial efforts on this problem I moved the pump even lower than the tank. Its immediately in front of the tank. Thanks everyone.
     
  8. 4thhorseman
    Joined: Feb 14, 2014
    Posts: 261

    4thhorseman
    Member
    from SW Desert

    3/8th line could be marginal if there are a lot of bends in it to feed a healthy 351W IMO. If the better pump don't solve it consider running a 1/2. You can pick up the aluminum 1/2 cheap and gently bend it up into place yourself with your hands.
     
    Last edited: Jul 17, 2014
  9. BucketHeadBart
    Joined: Jan 13, 2014
    Posts: 59

    BucketHeadBart
    Member
    from illinois

    So your gravity feeding the pump. maybe try 1/2 line from tank to pump to keep the pump fed when that xtra fuel is needed.
     
  10. Just for the heck of it,check your rubber hose between the gas tank and hard line,,it's a much overlooked small thing that can cause big trouble....mine was severely cracked and sucking air along with gas. HRP

    [​IMG]
     
  11. PKap
    Joined: Jan 5, 2011
    Posts: 593

    PKap
    Member
    from Alberta

    X2 on checking plumbing on the inlet side of the pump. I would also ensure that if you have a bend in the flex line, that it is not flattened out. On the gravity feed side of the pump I usually run hose a size bigger than the out feed side, in my experience it seems to reduce cavitation problems


    Posted using the Full Custom H.A.M.B. App!
     
  12. doctor chip
    Joined: Dec 10, 2010
    Posts: 82

    doctor chip
    Member
    from Delevan NY

    Yea I had a shutoff and a lot of plumbing between tank and pump that I got rid of last go around. The pickup in tank is 3/8 I think so not sure if larger line would help. I used new rubber from tank. I'll see what happens with the new pump and go from there. Thank you so much for the input.
     
  13. doctor chip
    Joined: Dec 10, 2010
    Posts: 82

    doctor chip
    Member
    from Delevan NY

    Got the Holley red pump and so far so good. I have read some reliability issues with this pump- does this continue to be a problem or has Holley got it fixed? Gauge is showing 7-8 lbs which is kinda high for edelbrock carbs. I know you can adjust this with the pressure relief valve with shims. To lower pressure do you take shims out?
     
  14. stimpy
    Joined: Apr 16, 2006
    Posts: 3,546

    stimpy

    shims out lower , only reliabibilty problems I know of are mostly not installed properly either electrical or plumbing . there noisy buggers ( buzz ) but if you insulate the mount with a chunk of rubber from the frame it quiets down the in car noise , but still buzzes outside . its the 2 pole motor that does it ..
     
  15. doctor chip
    Joined: Dec 10, 2010
    Posts: 82

    doctor chip
    Member
    from Delevan NY

    Thanks - I did the rubber thing and its actually quieter than the one I had in there.
     
  16. Good to hear the pump seems to have been the ticket. If your gremlins return look close at the pump suction as previously suggested. I restored a truck for the missus many years ago and all was fine for months until we hooked a big camper to it and tried to pull it 400 miles in the summer. The first big hill we had to pull the truck started popping through the carburetor at WOT. Not long after we were down to a top speed of about 25mph. The new 3/8" fuel line upstream of the stock fuel pump was soft enough that it would suck flat at sustained WOT. EGT got hot enough to drop two exhaust valve seats. Had to limp it home 150 miles on back roads with the boss complimenting my work the whole way!
     
  17. doctor chip
    Joined: Dec 10, 2010
    Posts: 82

    doctor chip
    Member
    from Delevan NY

    Well I took the relief valve out and only thing under the cap was a very small brass washer which I removed. No change in pressure, so I called Holley .They dont recommend tampering with pressure relief valve but say to get a blah blah dash blah blah pressure regulator. Was trying to avoid spending more on this issue but guess I'll have to unless one of you guys can suggest something else. Can high pressure damage the carb or just cause performance problems? Thanks again everyone - your the best.
     
  18. stimpy
    Joined: Apr 16, 2006
    Posts: 3,546

    stimpy

    depends on what carb you have , if it is a modern holley or oem style carb ( gm -ford , carter , holley ) , no it shouldn't but the old stroms and 94s from what all the guys here say they like low pressure ( real low like 3-4 psi ) .. I never liked to deadhead/ internal bypass a holley pump as they will cavitate when it gets hot . and also with low pressure you can stall the fuel in the line coming forward ( one of the reasons why they say regulate near the carb .
     
  19. yellow dog
    Joined: Oct 15, 2011
    Posts: 512

    yellow dog
    Member
    from san diego

    It sounds like problem solved....but best practice would be a bypass-return regulator mounted at float level (probably more $ than the pump however). Aside from that if you haven't observed
    the bowls puking over, the needles are holding. If the Edelbrocks use Viton needles like the old AFB's, this may eventually be a problem with ethanol blended gas (E85 for sure)......otherwise drive it and develop some confidence
     
  20. doctor chip
    Joined: Dec 10, 2010
    Posts: 82

    doctor chip
    Member
    from Delevan NY

    ok , got a regulator in and pressure set about 5 1/2 lbs. Hopefully everything fixed now. But since I replaced pump I notice fuel pressure will slowly drop after car is shut off. Before it wouldnt drop at all. Is this acceptable or do I have a bad check valve or something?
     

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