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Thread: 40 psi from Walbro 255 LPH pump.

  1. #1

    Default 40 psi from Walbro 255 LPH pump.

    Have an internal LP255 pump, but I'm only seeing 40 psi at the gauge on the inlet to the Sniper. Another gauge tried reads the same there. Tried a second gauge at the inlet to the filter, and it's the same pressure (40 psi), so filter not clogged. Any suggestions on where to start first?

    Do I need to drop the tank and check the connections in there as a first step or should there be another more obvious culprit?

    Car starts and idles fairly good so far, but is early going and would like to get the pressure correct before I continue further if 40 psi can cause problems. Thanks for any input.

  2. #2
    Join Date
    Dec 2009
    Location
    Connecticut
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    Default

    Ensure the fuel pressure regulator hasn't failed. The fuel pressure regulator sets the pressure.
    Fuel pumps don't produce pressure, they only flow volume.

    EFI fuel pumps have a wide range of psi capability; you set the exact pressure you need/want.
    Electric fuel pumps only produce volume, the fuel pressure regulator creates the desired pressure.

    Don't confuse psi ratings with what the pump is actually capable of.
    The psi ratings are for performance (volume) information only; they're not a pressure setting.
    Also, any EFI fuel pump will decrease volume output (GPH flow) as fuel pressure is increased.
    http://documents.holley.com/holleyfu...ems_chart1.pdf (Fuel System Selection Chart)

    This is a copy & paste of one of my other posts:
    Originally Posted by Danny Cabral
    A loud fuel pump is usually an indication of fuel pump cavitation or maybe a clogged filter(s). Inspect/troubleshoot/service the fuel system (fuel pump, cavitation, plumbing, voltage, filters, pickup tube, tank venting, etc.). A datalog will just verify a problem with the fuel pressure, injector duty cycle, pulse width, etc.

    An EFI fuel system needs two filters:
    Before fuel pump - 100 micron pre-filter. (Or the OEM in-tank sock filter.)
    After fuel pump - 10 micron post-filter. (40 micron is for carburetion.)
    The 40 micron (carburetor) fuel filter has no place on an EFI fuel system. (I know you're not using it.)
    It's too "fine" of a filter to be used before the pump, causing fuel pump cavitation.
    FYI: The sock filter (HydraMat or OEM) of an in-tank fuel pump, is the pre-filter. Don't add another one.
    http://documents.holley.com/holleyfu...ems_chart1.pdf (Fuel System Selection Chart)
    http://documents.holley.com/flyer_ho...el_systems.pdf (Holley Fuel Systems Brochure)
    https://forums.holley.com/showthread...395#post223395 (Related Forum Thread - NAPA 20 Micron Pre-Filter)
    Contact Chris Myer at EFISystemPro.com. He's a Holley EFI parts professional, Holley EFI Dealer & fuel pump/fuel system specialist.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385"/6.3L SBF, Dart SHP 8.2 block, forged steel crank & rods, forged pistons, Trick Flow T/W 11R 205 CNC comp ported heads, 12:1 comp ratio, 232°-244° duration/.623" lift/114° LSA camshaft, TFS R-Series FTI comp ported intake, BBK 80mm T/B, Holley Dominator MPFI & DIS, Holley 36-1 crank trigger, MSD 1x cam sync, PA PMGR starter, PA 200A 3G alternator, Optima Red battery, 100HP progressive dry direct-port NOS, R134a A/C, Spal dual 12" fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, Earl's -6AN fuel system plumbing, Walbro 255 LPH in-tank pump & Pro-M -6AN hanger, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM C6 converter, B&M Hammer shifter, Stifflers transmission crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  3. #3

    Default

    If you're using the Sniper built-in pressure regulator that's what determines your system pressure before & after the filters and at the Sniper inlet. If the pressure regulator is dirty or not working properly you can see a reduced pressure. If you have the fittings, disconnect the inlet hose fitting into the Sniper. Cap that hose and then cycle the pump and measure the pressure on the supply side. If it's still 40 you may have a pump problem as you currently suspect. If you see 80 or 90 psi on the capped line then the Sniper regulator is suspect. Report back on your findings.

    The above assumes you are running a full return with the Sniper internal regulator. If configured differently, please detail your fuel system from the pickup in the tank all the way to the Sniper (and back if appropriate).

  4. #4

    Default

    Good idea. I'll try that to narrow it down further. Yes, I'm using the internal Sniper regulator and return. Thanks.

    UPDATE: Still at 40 psi bypassing the fuel pressure regulator. So it must be in the tank connections for the pump, or a faulty pump. Will drop it in the morning. Thanks!

  5. #5

    Default

    Now I'm seeing 70 psi on the input side. Any thoughts there? Sniper regulator clogged?

  6. #6
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
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    See post #2 above. Replace the Sniper EFI fuel pressure regulator (LINK).
    https://forums.holley.com/showthread...8356#post88356 (Holley Sniper EFI Fuel Pressure Tester/Gauge)

  7. #7

    Default

    @74mopar: I’ve seen a bunch of cases where the hose between the pump and the top of the tank outlet has split. This happens when hose that’s not rated for submersible use, was used in the installation. Andrew

  8. #8
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    31,483

    Default

    Stop using rubber fuel injection hose in the fuel tank, even if it is SAE 30R10 rated for in-tank (immersion) use. Use PTFE corrugated fuel pump pressure hose with fuel injection hose clamps (LINK).
    https://forums.holley.com/showthread...nts-amp-Clamps (Proper EFI Hose, Sealants & Clamps)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385"/6.3L SBF, Dart SHP 8.2 block, forged steel crank & rods, forged pistons, Trick Flow T/W 11R 205 CNC comp ported heads, 12:1 comp ratio, 232°-244° duration/.623" lift/114° LSA camshaft, TFS R-Series FTI comp ported intake, BBK 80mm T/B, Holley Dominator MPFI & DIS, Holley 36-1 crank trigger, MSD 1x cam sync, PA PMGR starter, PA 200A 3G alternator, Optima Red battery, 100HP progressive dry direct-port NOS, R134a A/C, Spal dual 12" fans, Frostbite 3-core aluminum radiator, Pypes dual 2.5" exhaust, off-road X-pipe, shorty headers, Earl's -6AN fuel system plumbing, Walbro 255 LPH in-tank pump & Pro-M -6AN hanger, S&W subframe connectors, BMR upper & lower torque box reinforcements, LenTech Strip Terminator wide-ratio AOD, 3000 RPM C6 converter, B&M Hammer shifter, Stifflers transmission crossmember & driveshaft safety loop, FPP aluminum driveshaft, FPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 M/T Street Comp tires.

  9. #9

    Default

    Yes, it was the outlet side of the pump, where the hose clamp had failed and was not tight enough to hold the pressure within the tank.

    Then the pressure was 70-80 psi at the gauge, so I took the screen off the regulator in the Sniper and it shows steady 55 psi now. I ordered a new regulator for it, but I'll watch it and make sure it holds steady and may just roll with it like this.

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