Voltage issue?

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Plsdontflip, Jan 24, 2022.

  1. Plsdontflip

    Plsdontflip Light Load Member

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    Oct 10, 2021
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    Ok so let me give you y usual preface of I'm no mechanic, and not mechanically inclined but I do know the bare basics a man should know.

    Ok the problem arose last week around Thursday on my load home. I noticed my voltmeter said 12.8 or so rather my usual 13.6 to 14.1 or so. Parked it next day for the weekend, went to crank Monday afternoon to get my next load, it hesitated and made its noises slowly before starting. Voltmeter at around 12.5 or so now. Drive it to get fuel and it's at 12 now, maybe 11.9 because light came on. At this point I checked the alternator with multimeter. It's pushing out 14.35 volts. Take steps off check batteries, all the batteries show 12.5 or so. Decide to drive to pick up see what happens. Randomly gets back up to 13.5 volts and light cuts off. Have checked alternator at least 10 times It's never less then 14. Load tester indicates all batteries are good. I changed some ugly wires and fittings, and a couple potential loose grounds I saw. It's at like 12.2 right now when earlier it was 14 when I started my day. It's a 2015 international prostar. Any ideas what I should try or look at before giving to a shop and wasting money I feel like this is something I could do with a little guidance.
    Thanks in advance!
     
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  3. AModelCat

    AModelCat Road Train Member

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    Check the wiring from the alternator all the way back to the batteries. Power and ground side. Much of the ground circuit will be through the engine block and frame so make sure the alternator is bolted up tight. Also check the ground strap between engine and frame as well as the ground cable from batteries to the frame.
     
  4. baha

    baha Road Train Member

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    Alt. Is showing signs of failure, next rainy night when you are are running headlights and fans on hi ck if it can keep batteries fully charged?
     
  5. Plsdontflip

    Plsdontflip Light Load Member

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    Oct 10, 2021
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    Yeah I keep a close eye on it and check all frequently. Maybe it's just me but I swear I can hit a bump and lose all my voltage then hit another and be back at 14 lol
     
  6. loudtom

    loudtom Road Train Member

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    I had a similar issue, where the dash was showing 12.6-13.4 while running. But when I tested it with a multimeter, alternator was showing 14.1 when probed, and the batteries were at 13.9. The problem ended up being a maxi fuse between the battery and the power for the truck. It was failing internally, so every time I'd hit a bump or anything, it would fluctuate. As a temporary fix, I bypassed the fuse and went directly to the battery until I could get a replacement. Even if this is not your issue, it's not a good thing to postpone fixing. With the batteries being on the driver side, it's terrible to try and fix it while on the side of the road.
     
  7. Plsdontflip

    Plsdontflip Light Load Member

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    Oct 10, 2021
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    Last truck stop I was at I changed a ground cable going to the alternator that was rotting to bits and another connection I found between the frame and engine that had rotted all green and it seems to actually be holding now will update. Thanks all.
     
    baha and loudtom Thank this.
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