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Thread: 12-700 Fuel Pump - Rebuild?

  1. #1

    Default 12-700 Fuel Pump - Rebuild?

    My 12-700 fuel pump is powered through the HP EFI system.
    The pump was working fine. It auto primed and ran as needed while cranking. But after an hour or two of working through new system start up issues the pump has already quit working. It's dead to direct +12V input on a bench test.

    I have a 100 micron pre-filter installed, pump is mounted external and below the tank in the same place the low pressure pump lived.
    Why did my pump die this quickly? Doesn't the HP wire harness already have a fuel pump relay built-in?

    Can it be rebuilt? I would think the pump itself is fine, but the motor is the issue?
    Is the pump sensitive to fuel cavitation or starvation? If so, would it cause this problem? My fuel tank is low, maybe an 1/8 tank.

  2. #2
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    Quote Originally Posted by 421 Fuellie View Post
    Doesn't the HP wire harness already have a fuel pump relay built-in?
    Yes, it's called the system relay. The system relay's coil is grounded at terminal #85 by the loose black wire.
    The ECU's J1A-A2, (22 AWG red wire) energizes +12V the system relay coil at terminal #86,
    during the 5 second Fuel Pump Prime time, when cranking, and when the engine is running.
    There's a fuse next to the system relay, that powers the relay (14 AWG red wire) at terminal #87.
    The system relay activates the fuel pump, and powers the fuel injectors (& ignition coils - LSx, MOD & HEMI) from terminal #30.
    The ECU pulses the ground side of the injectors to spray fuel.
    http://documents.holley.com/techlibr...10555rev17.pdf (Holley EFI Wiring Manual, Section 13 - Wiring Appendix)

    I've never used the ECU's fuel pump trigger wire to directly power the pump (even if it is less than 10 amps).
    I've always used a separate relay (shown below) because that green wire is still only 14 AWG.
    The 2nd fuel pump relay is used so the fuel injectors aren't subjected to the pump's amp draw.
    It's only a 20 amp fuse and it also feeds power to the fuel injectors (& ignition coils - LSx, MOD & HEMI).
    I prefer to use 10 gauge wire due to its long length, especially for high output race pumps.
    Simply use the green fuel pump wire (+12V) to trigger your additional fuel pump relay's coil (+) terminal #86.

    https://www.holley.com/products/fuel...s/parts/12-753 (Holley 12-753 Fuel Pump Relay Kit)
    http://documents.holley.com/199r10059.pdf
    (Holley 12-753 Fuel Pump Relay Kit Instructions)
    https://www.holley.com/products/fuel...arts/30-199QFT (Quick Fuel 30-199QFT Fuel Pump Relay Kit)
    https://www.holley.com/products/fuel...s/parts/40100G (Mr. Gasket 40100G Sealed Relay Kit)
    https://www.summitracing.com/parts/pco-5593pt/overview/ (Pico Wiring 5593PT Sealed Relay Kit)
    Delphi Metri-Pack 630 Pull-To-Seat female terminals for retrofitting to a sealed relay socket connector:
    #12033997 10/12 AWG (3.0 mm²), #12066614 14/16 AWG (2.0-1.0 mm²), #12020156 18/20 AWG (0.80-0.50 mm²)

    Can it be rebuilt? I would think the pump itself is fine, but the motor is the issue?
    You'll have to contact Holley Tech about warrantying the fuel pump.

    Is the pump sensitive to fuel cavitation or starvation?
    All electric fuel pumps are susceptible to damage from cavitation or fuel starvation.

    If so, would it cause this problem? My fuel tank is low, maybe an 1/8 tank.
    Depends if it was sucking fuel or air (or aerated fuel).
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, 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.

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