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  1. #1
    FEP Senior Member 9DBlackMagic's Avatar
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    Sep 2006
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    Default Question about alternator volts

    Hello fellow members,
    Hi my name is Les I just put in a 91 roller motor that's all stock except the new drop roller lifter, push rods and a new e-cam. I also did a 3g upgrade before the 91 motor it was pushing normal voltage with the all stock 82 motor. Now I just got it running and it's putting out 11.4 volts while running. I had the battery charged and tested and the said that the battery is at 40%. Could this be the problem.
    ~LES~
    157 HP @ 4200 RPM
    240 ft/lb @ 2400 RPM

    "Yeah Baby Feel That Pure Power"
    Capri:
    Is a Mustang With Hips And Class

  2. #2

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    If you dont have at least 13.8 volts while running then you are not charging correctly. Regardless of battery you should still see this voltage. So no. Its not the battery causing it not to charge, though it still may be bad.. I'd think you have a wiring issue somewhere. Most 3G conversions have a self energizing plug, so all you do is connect the 1 wire to the battery. If you have this setup, I would check this to make sure its in there correctly, and make sure you have a good ground. Negative battery cable to the motor, and negative battery cable to the chassis. You need both grounds.

  3. #3
    FEP Senior Member 9DBlackMagic's Avatar
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    Oh ok thanks capri-magic
    ~LES~
    157 HP @ 4200 RPM
    240 ft/lb @ 2400 RPM

    "Yeah Baby Feel That Pure Power"
    Capri:
    Is a Mustang With Hips And Class

  4. #4
    FEP Senior Member BMW Rider's Avatar
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    Oct 2014
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    Calgary, Alberta, Canada
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    Voltage output will vary based on the battery voltage. It will generally run about 2v higher than battery. Also, the alternator will usually not produce full voltage at low engine speeds particularly if there is a lot of electrical demand. To determine if the alternator is charging you'll need to measure the base battery voltage first, then check with the engine running at at least 1000 rpm or more.

    That said, 11.4 does seem quite low.

  5. #5
    FEP Super Member erratic50's Avatar
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    Dec 2016
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    Default

    Underdrive pulleys can influence low rpm but I agree.

  6. #6
    FEP Super Member
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    May 2003
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    Roseburg Oregon
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    Default

    Sounds like you have lost the exciter circuit , that makes the alt. charge , you are on battery voltage only.

    Battery should be 12 -12.50 or so cor a fully charged battery , with engine running , no less than 13.5 volts , usually 14 -14.5 with a load and 2500 rpm.

    Anything less , and you are draining your battery , it will die .
    clowns to the left of me , Jokers to the right

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