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Thread: low fuel pressure

  1. #1
    Fuel Injected!
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    low fuel pressure

    In hard acceleration fuel pres. drops to about 5lbs.new pump(twice)3/8"supply line,pressured tank to help siphon(inline 2000 pump)pinched off return (helped a little but not enough)new filter,this has been going on for some time and tuning is impossible.This is on a built 350 with 90lb. injectors running just under 14lbs. of press.when at idle and when return is restricted, press. rise a kills engine like it should.

  2. #2
    EFI GearHead ! EagleMark's Avatar
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    Where is pump located? Wiring to pump, what gauge? Charging system voltage when happening?

    But more then likely... that pump sucks for more then a stock engine.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  3. #3
    Fuel Injected!
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    Pump is on frame apx. even with bottom of tank.fuel gauge is connected inline right in front of pump.voltage is 14 or above and wiring is factory wire from donor vehicle Pump is for a ford big block and it starts dropping off around 3000rpm.

  4. #4
    Fuel Injected!
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    Quote Originally Posted by EagleMark View Post
    Where is pump located? Wiring to pump, what gauge? Charging system voltage when happening?

    But more then likely... that pump sucks for more then a stock engine.
    Tend to agree with Eagle and your symptoms back that up at idle it's able to sustain but loaded the duty cycle's killing your pressure. Depending on the vehicle and it's use you may want to research an in tank drop in pusher. It'll run cooler and live longer as well.

  5. #5
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by mdj View Post
    Pump is on frame apx. even with bottom of tank.fuel gauge is connected inline right in front of pump.voltage is 14 or above and wiring is factory wire from donor vehicle Pump is for a ford big block and it starts dropping off around 3000rpm.
    If the wire is small gauge... it may not be able to keep up with voltage demands of pump under high load. Example there are Hot Wire kits for the LT1 vehicles with this issue.

    But dropping to 5 PSI is pretty bad and probably more likely a combination of not enough wire gauge and pump just can't keep up.

    You may also be experiencing the fuel line and/or filter between pump and tank collapsing? Or if plumbed to an old stock tank the inlet is usually 5/16 and the fuel pump feed requires a 3/8th line. I've gotten away with this if sock is removed from the tank in small low HP engines!

    Your basing the pumps ability on the fact it's for a Ford V8 and BB too, but specs are Minimum Free Flow Rate (gph) 30 but that is at 70-95 PSI... and only 5/16th hose.
    http://www.autozone.com/autozone/par...ntifier=386516

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  6. #6
    Fuel Injected!
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    Looking into a in tank install for the fuel cell. Any suggestions on a good pump that is a reasonable price,Plan on fabricating some type of hanger in tank for pump.Apx, 400 horse in engine. Will be increasing pressure to about 18lb. when I get pump problems figured out.(81lb, injectors not 90 lb).this is in a crawler 5500rpm max

  7. #7
    EFI GearHead ! EagleMark's Avatar
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    Carter p5000 is from TPI and handles all the TBI high pressure needs. But it does whine so lots of guys don't like it, should not be an issue on a crawler.

    This is the best route:
    http://www.gearhead-efi.com/gm-ecm-p...onversion.html

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  8. #8
    Fuel Injected! 1BadAction's Avatar
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    Quote Originally Posted by EagleMark View Post
    Is the factory mounting ring on a TBI tank the same as the mounting ring on a bucket style tank like that is from?
    2010 Porsche Cayenne GTS - DD
    1991 2500 Suburban - 454ci BBC tow monster
    1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac

  9. #9
    EFI GearHead ! EagleMark's Avatar
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    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  10. #10
    Fuel Injected! brian617's Avatar
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    Quote Originally Posted by 1BadAction View Post
    Is the factory mounting ring on a TBI tank the same as the mounting ring on a bucket style tank like that is from?

    Negative
    89 K1500 Scottsdale 5.7L 5spd 3:42

    Build specs: 97 4 bolt main block 350ci, Eagle rotating assembly with flat tops and 4 valve reliefs, Dart 165cc/67cc Iron Eagle heads, Manely SS valves and springs 110lbs seat @1.7, GM Ram Jet cam 196/206 @.50 .431/.451, stock intake and throttle body, heads and intake gasket matched, Delco EP377 fuel pump @ 22 psi, 427 PCM.

  11. #11
    Fuel Injected! 1BadAction's Avatar
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    Quote Originally Posted by brian617 View Post
    Negative
    Guess that shoots that idea in the ass. Thanks for the info.
    2010 Porsche Cayenne GTS - DD
    1991 2500 Suburban - 454ci BBC tow monster
    1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac

  12. #12
    EFI GearHead ! EagleMark's Avatar
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    But for a factory TBI tank you just change the pump to TPI or 96 Vortec...

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  13. #13
    Fuel Injected! brian617's Avatar
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    Quote Originally Posted by 1BadAction View Post
    Guess that shoots that idea in the ass. Thanks for the info.
    Anytime I can squash your ideas i'm glad to help

    What year truck are you working on?
    89 K1500 Scottsdale 5.7L 5spd 3:42

    Build specs: 97 4 bolt main block 350ci, Eagle rotating assembly with flat tops and 4 valve reliefs, Dart 165cc/67cc Iron Eagle heads, Manely SS valves and springs 110lbs seat @1.7, GM Ram Jet cam 196/206 @.50 .431/.451, stock intake and throttle body, heads and intake gasket matched, Delco EP377 fuel pump @ 22 psi, 427 PCM.

  14. #14
    Fuel Injected! 1BadAction's Avatar
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    Quote Originally Posted by EagleMark View Post
    But for a factory TBI tank you just change the pump to TPI or 96 Vortec...
    I like the bucket style better, they seem to have a more consistent fuel draw when empty but since it's not a somewhat direct swap then I'll just go ahead with a TPI pump in the stock type hanger. A new sender should help somewhat, at 1/4 tank on the gauge I have roughly 2 gallons in the tank, and with the way I drive 2 gallons doesn't get me far.
    Quote Originally Posted by brian617 View Post
    Anytime I can squash your ideas i'm glad to help

    What year truck are you working on?
    Hey, it saved me some cash or time at the auto parts store fooling with it Finally starting to get my Suburban (see sig) where I can start modding. Tune is spot on other than I'm running out of both fuel and air. With 102 atmosphere, at WOT it's 90Kpa at 3000 and vac increases to high 80s from there, at 13psi it's still wanting more fuel with the IDC into the 90s. The minute I put the ported edelbrock intake and bored TB on it, I'm going to need even more fuel.

    I also suspect the fuel pump isn't holding pressure when I snap the throttle open, I have the AFPR adjusted to what should be 18psi but all it'll give me is 13. I have the fp gauge but don't have what I need to read it while in the truck with the hood closed.
    2010 Porsche Cayenne GTS - DD
    1991 2500 Suburban - 454ci BBC tow monster
    1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac

  15. #15
    EFI GearHead ! EagleMark's Avatar
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    Quote Originally Posted by 1BadAction View Post
    I have the fp gauge but don't have what I need to read it while in the truck with the hood closed.
    Plumb it to a gauge on the hood you can see!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

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