Charging Change

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by kchecca, Nov 6, 2001.

  1. kchecca

    kchecca Registered Member

    Sep 26, 2001
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    Feeding Hills, MA
    Good afternoon all. Still rolling the K5 rebuild and I came across an odd problem with the charging. It seems to run fine and sit at ~14.5V at all times except in the rain.

    Once it gets wet, I will see the voltage drop to 11-13V at idle and the idle gets rough. It will mostly go back up at speed, but there is a clear drop and roughness during idle.

    Is this a sign of dead battery cables and/or plug wires? The battery is 3 years old (Die Hard) and I have no idea on the alternator. I have had a rough wet-idle problem with other vehicles that was the plug wires, but never the charging issue. Anyone with ideas?

    Keith C
    Bigbird '00 Jeep TJ
    Grandpa's '77 Blazer
  2. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

    Feb 17, 2000
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    Well we need a little more info. is it "Grandpa's '77 Blazer" that is having the problems? The rough idle sounds weird. if it's a 77 it's pre anything electronc controled on the engine. Once started the engine should run with as low as 10V before the HEI starts freeking out. Raining usualy means lots of electrical load. All lights and whipes on any maybe defrosters and A/C if it works. My off the top of my head guess would be a bad Alternator that is not produscing enough power. Other problems would be shorts on windshiel wiper motor that's putting an unusual amount of draw on the electrical system. Check the fuse links at the starter for any signs they have blown and been replaced with possibly the to high of amp fuse link or worse yet a peice of wire. Also check for corrosion on the wires down there. All the power for the truck routes off the starter and with it down low it's usualy getting wet.

    Women dig dents and flat paint!
    75 Jimmy, Dollar
  3. HarryH3

    HarryH3 1 ton status Author

    May 31, 2000
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    Georgetown, TX
    How old and brittle are the spark plug wires? Sounds like the wires are leting moisture in and letting lots of your spark go to the block instead of to the plugs. The low idle may be causing the low alternator output, instead of vice versa.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <a target="_blank" href=></a>
    It's a great day to be alive...
  4. TorkDSR

    TorkDSR 1/2 ton status

    Sep 1, 2001
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    bucks co pa
    the low amp output is due to the low idle, now what the low idle is due to could be a few things......

    my first guess would be the cap and rotor. look at the inside of cap to see if you can spot any crossfire marks. if the cap is bad, then damp air will only help it to crossfire....

    second guess is wires, go out at night and, while running, spray the engine down with a garden hose and look for sparks jumping around, they're blue, and not always easy to see.

    and thats all i have to say about that.

    Tork DSR
    "Easy killer. That's technology you talk of..."

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