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Electric Vs Mechanical Fuel Pump?

Discussion in 'Early CJ5 and CJ6 Tech' started by Jonbbrew, Feb 28, 2020.

  1. Feb 28, 2020
    Jonbbrew

    Jonbbrew Member

    Paso Robles, CA
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    My 198 had a electric fuel pump installed but has issues. Replace or better to go back to mechanical ?

    Thoughts? Preferences? Why?

    thank you!
     
  2. Feb 28, 2020
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    I’m a fan of the little chatterbox pumps. They will prime your carb unlike a mechanical pump, they won’t fill your crankcase with gas when they fail, and if your old one still sorta works, throw it in the glove box for a spare.
     
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  3. Feb 28, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    Not sure the crankcase issue is much of an advantage. Without some added circuitry, an electric pump will keep running as long as the key is on. Now a stuck float will flood out the bowl vents and down into the cylinders and past the rings. A wreck or rollover will keep pouring gas out until the key is off.

    You can address the roll-over problem with an oil pressure safety switch, which will shut off the fuel pump when the engine shuts off. A spring-loaded toggle on the dash helps with priming. Or you can buy one of the electric fuel pump controllers that will automatically prime if needed. Apparently some Fords have a rollover switch that you can add to the circuit.

    Seems like mechanical pumps are not as reliable today as they once were. I have had a couple fail after just a year or two in service. I have a Spectra in my J20 now, and it seems to be holding up ok. The two previous Airtex pumps (J20 and J10) both stopped working. In concept, the mechanical pumps should be very reliable, but possible the market for old car parts cannot support quality brands any more. Do you have a line on a mechanical pump? RockAuto shows nothing for a '63 Skylark with a 198. The aftermarket may make that decision for you. (Napa shows one. Amazon shows a Carter - likely the same as what Napa sells)
     
    Last edited: Feb 28, 2020
  4. Feb 28, 2020
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Hills of NH
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    I actually had the cylinders on my 360 J-truck hydro-lock from gasoline, thanks to an electric pump.

    Parked on a hill and the in-cab fuel tank was higher than the carb. Flooded all night.
     
  5. Feb 28, 2020
    Jrobz23

    Jrobz23 Member

    Northern, WI
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    I like mechanical pumps when I can get away with one.
     
  6. Feb 28, 2020
    CHUGALUG

    CHUGALUG Member

    Silverton, OR
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    No electric fuel pump should be used without an Oil Pressure Safety switch and the proper fuse. I've run like 6) different Electric fuel pumps and they all need the safety of an Oil pressure switch. Engine no run or your finger isn't on the starter button the pump will not operate. Holley has an excellent wiring diagram on line.

    By the way except for the Carter old school pump that went out in the Wifes 67 Mustang (did have almost 125K on it). They have all performed very well.
     
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  7. Feb 29, 2020
    Rick Whitson

    Rick Whitson Detroit Area 2024 Sponsor 2022 Sponsor

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    That is the first time I have ever heard of an oil pressure switch for an electric fuel pump, makes a lot of sense. I just saw that on a Diesel stationary motor I bought, it had a switch on the oil pressure that turned on the alternator exciter to make it charge while running, and turn off the exciter when not running, something I never give a thought to. I was never a fan of electric fuel pumps, me uncle watched his Jaguar XK140 burn to the ground because of one. Good Luck
     
  8. Feb 29, 2020
    Dphillip

    Dphillip Member

    Omaha NE
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    My opinion: Electric fuel pumps have become so reliable that most manufacturers are now offering lifetime guarantees with their units. I also believe it’s best to mount a electric pump in the tank as oppose to an inline pump because it’s easier to push fuel out of the tank rather than pull fuel from the tank.
     
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  9. Feb 29, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    How about a reliable fuel pressure regulator to go with an electric pump? Who has a source for a good one that actually works and lasts more than a day?
     
  10. Feb 29, 2020
    CHUGALUG

    CHUGALUG Member

    Silverton, OR
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    Glenn check out the Holley unit that runs 1-4 psi I have had very good luck with them holding the 2.5 psi Weber carbs like. I have my pump in my 2A mounted on the back side of the riser with the pickup at the same level as the fuel line is once it makes a 90° coming out of the tank. This way the tank is above the input on the pump. Works very well. I'm running a Holley Red pump (a street pump 7psi)
     
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  11. Feb 29, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Out-of-the-tank pumps are recommended to be mounted lower than the fuel level, or as low as possible. If mounted as low as an in-tank pump would be, I can't see how physically the load on an outside pump would be meaningfully higher. There would be a really minor flow restriction in the siphon to the pump, but the siphon due to be gravity would be way way faster than you'd ever need fuel. A totally dry tank might be harder to prime for an exterior pump, but how often does your tank run completely dry? I have heard that fuel injected cars with factory in-tank pumps can also have trouble priming after refilling a completely dry tank.
     
  12. Feb 29, 2020
    Dphillip

    Dphillip Member

    Omaha NE
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    I believe, easier to push fuel from the tank rather than pull fuel from the tank is more evident in higher elevations. It’s my understanding that altitude changes pressure in the fuel tank.

    In my own experience, I once had a Howell FI system with inline electric pump on my original motor a 258 straight six. Engine ran great except for trips to the mountains of Colorado where I experienced repeated stalling. Several FI techs recommended an in tank pump specifically because of the push pull scenario.
    After install of an electric pump I’ve never had that problem again.
     
  13. Feb 29, 2020
    47v6

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    This thread is something I am thinking about because of my 4.3 FI chevy engine I will be installing. I really don't want to go with an in tank fuel pump that I will have to modify my existing 76 tank.

    Are there retrofit kits that install inside the tank with minimal or no modification?

    Are there eternal volume pump and then pressure booster pumps that are external?

    Any experience?
     
  14. Feb 29, 2020
    PeteL

    PeteL If it wasn't for physics, and law enforcement... 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    All true, I believe. But it's not simply about "load."

    A mechanical (or electric) pump near the engine is drawing fuel a long way under vacuum, and with significant friction losses in the line. Add some heat, and the vapor-pressure of a volatile fuel, and vapor locking becomes more likely.

    As I'm sure you know, the maximum theoretical Delta-P (pressure differential) under a vacuum is about 14PSI. And, in a fuel line, the vacuum is encouraging vapor formation. OTH, under compression, say on the output side of a fuel pump, the pressure delivered can be almost limitless, and no vapor.

    Which is simply to say this is why some antique car guys developed the practice of converting to electric pumps in or near the fuel tank.
     
    Last edited: Feb 29, 2020
  15. Feb 29, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    If the diaphragm and check valves are good a mechanical fuel pump shouldn't have any trouble pulling fuel, especially with a CJ size vehicle. They do say to push fuel with an electric pump.
     
  16. Feb 29, 2020
    CHUGALUG

    CHUGALUG Member

    Silverton, OR
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    An electric pump will not suffer vapor lock if its located close to the Tank
    An electric pump will prime and empty float bowl in a couple seconds
    An electric pump that fails just stops delivering fuel to the engine no leaking into the crankcase or leaking down of the fuel line.
    An electric pump will not work with a dead battery (but then neither will a coil) so thats kind of moot.
    An electric pump can be set up with a manual shut off that can operate as an anti theft device
    An electric pump should ALWAYS have an Oil pressure safety switch in the circuit to prevent running unless the engine is running (the starter button or position on the switch acts as a by pass for starting)
     
  17. Feb 29, 2020
    Dphillip

    Dphillip Member

    Omaha NE
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    My in tank fuel pump was quite easy to fabricate. I shortened the fuel pick up tube that come down from the sending unit. I used a short piece of submersible rubber fuel line and attached one end to the shortened pick up tube and the other end to the electric fuel pump. A small hole was drilled in the sending unit to run the power and ground wires to the pump and that hole was then sealed up with JB Weld.
     
  18. Feb 29, 2020
    ITLKSEZ

    ITLKSEZ Hope for the best, prepare for the worst

    Liberty Lake, WA
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    Volvo might find issue with that statement. When they began using fuel injection in the 70s, they had a single pump that was about a foot in front of the tank under the car. A year or two later, they added a small in-tank pusher pump to supplement the main pump due to reports of vapor lock. That setup remained in place up into the 90s.
     
  19. Feb 29, 2020
    colojeepguy

    colojeepguy Colorado Springs

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    This might be an option for you
    Fuel Tank Sump # 36032 35-90 PSI 67 GPH/255 LPH
     
  20. Feb 29, 2020
    45es

    45es Active Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

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    Chris, bite the bullet and do the in tank pimp. The benefits out way the negatives. Hopefully you kept the pump and parts from the Astro.
     
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