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New alternator, but voltage isn’t constant.

Discussion in '2nd Gen Tundras (2007-2013)' started by aidan_pierce, Oct 30, 2024 at 12:48 PM.

  1. Oct 30, 2024 at 12:48 PM
    #1
    aidan_pierce

    aidan_pierce [OP] New Member

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    Alright guys, i got my new alternator in, and my battery is brand new. However, when running, the voltage meter keeps dropping and jumping back up. Anyone know what this could be? Bad connection? Loose wiring? Anyone else had a similar problem?
     
  2. Oct 30, 2024 at 1:47 PM
    #2
    mtucker

    mtucker New Member

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    Make sure serpentine belt is correct?

    large.jpg
     
  3. Oct 30, 2024 at 1:49 PM
    #3
    aidan_pierce

    aidan_pierce [OP] New Member

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    I wasn’t sure the thing would even run if it was wrong but shoot i might double check ‍♂️
     
  4. Oct 30, 2024 at 1:49 PM
    #4
    bfunke

    bfunke Tundra Curmudgeon

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    Tell me it’s a Denso and not some POS Chinesium aftermarket part.
     
    AZBoatHauler and KNABORES like this.
  5. Oct 30, 2024 at 1:53 PM
    #5
    blenton

    blenton New Member

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    Define 'dropping and jumping back up'; what range are you seeing? Alternator supplied voltages fluctuates with RPM and electrical load/demand, especially just after startup. Cruising down the freeway it will be fairly level.
     
  6. Oct 30, 2024 at 1:57 PM
    #6
    aidan_pierce

    aidan_pierce [OP] New Member

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    Well I was down a vehicle and couldn’t go another day without it fixed so I just bought an Ultima from Oreilleys, almost 400 bucks. heard they aren’t the best but it had a 4.8 star rating and so I bit the bullet.
     
  7. Oct 30, 2024 at 1:58 PM
    #7
    aidan_pierce

    aidan_pierce [OP] New Member

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    By jumping I mean idling at about 14 volts and dropping to around 10-11 randomly. It starts perfectly and runs great when driving. But stopped It completely dims out my lights and AC almost shuts off.
     
  8. Oct 30, 2024 at 2:00 PM
    #8
    mtucker

    mtucker New Member

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    I recently watched a Youtube video of a guy that was looking at a 5.7l that had the belt replaced, but it was squeaking. The previous mechanic put it on wrong. I looked in my Youtube history, but couldn't find it. I don't think a charging problem was listed, but it ran ok with the belt in wrong.
     
  9. Oct 30, 2024 at 4:13 PM
    #9
    Chuy!

    Chuy! New Member

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    That drop is excessive. Below 12.6 volts and the alternator is not charging at all. Sounds like the voltage regulator in the alternator is defective. Have Oreilly check it if they have a device that can check the charging system with the engine running.
     
  10. Oct 30, 2024 at 8:27 PM
    #10
    aidan_pierce

    aidan_pierce [OP] New Member

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    Had the workers test it and they said the alternator was perfectly fine. Passed everything. So that’s why I think it’s a bad connection somewhere. Are there wires or connectors that commonly or possibly go out that could result in this?
     
  11. Oct 31, 2024 at 1:52 PM
    #11
    bfunke

    bfunke Tundra Curmudgeon

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    Battery cables corroded?
     
  12. Oct 31, 2024 at 2:19 PM
    #12
    CreekDweller

    CreekDweller Not so new ...

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    Worth checking if the ground wire from the battery to the engine has a good connection. From your description it sounds as if current is flowing from the alternator to the battery, but not at a sufficient rate to keep up with demand, which could be due to a bad connection. A bit like what you wrote yourself about thinking is might be a wiring problem.
     
  13. Oct 31, 2024 at 8:15 PM
    #13
    lr172

    lr172 New Member

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    With a charged battery, the voltage should drop from 14 to around 13 or 12.5 if the alternator stops charging. The fact yours drops to 10 indicates a wiring issue on one of the thick lines, likely something connected to the battery or the line from the battery to the alternator
     
  14. Oct 31, 2024 at 8:30 PM
    #14
    10 Bears

    10 Bears New Member

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    None at the moment
    Double check your connections. Otherwise remove & bench test that alternator.
    Where did you buy & what brand is it ?
    Modern cars are SOOOOOOO sensitive to sub par electrical components.
    You'll know very fast.
     

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