Suburban battery charges only during idling or acceleration

Discussion in 'GM Electrical Tech' started by E Boyd Daniels, Jun 14, 2013.

  1. E Boyd Daniels

    E Boyd Daniels New Member

    The battery only charges when I'm at idle and in gear or when accelerating, voltage drops to 12v or less when I'm cruising or deccelerating & the battery light comes on. I've changed the alternator, the battery, every corroded connector or contact I can find, changed the serpentine belt and the tensioner and nothing changes or fixes the problem. I used my multimeter to measure actual voltage from the alternator and it tracked 1 to 1 with the dash gauge under actual driving conditions.
  2. Conlan Rose

    Conlan Rose Epic Member 5+ Years 1000 Posts

    What's the year, and engine of your burb? Because if it is a new vehicle it may be the BCM or if its a much older one it might be the voltage regulator.

    Your issue is the opposite that most have usually at idle or acceleration the voltage drops from an increase in load or lower rpms and while cruising and decel the voltage raises.
    Best things to do no matter the year truck:
    Check every ground everywhere on the truck
    Make sure all electrical connections are clean and tight.
  3. E Boyd Daniels

    E Boyd Daniels New Member

    Sorry, I have a '98 C2500 2WD with the 7.4L engine.
  4. Conlan Rose

    Conlan Rose Epic Member 5+ Years 1000 Posts

    Ok, then I have much more of a clue how to help. Your truck is the same gen as mine, I have a 96 K1500 4x4 Tahoe with the 5.7L, these trucks have no BCM and the ECM does little to control alt output. Also their alts are internally regulated so we can likely rule that out.

    In my experience in my truck, before I got my current alt and upgraded power and ground cables, when cold at accel I would gain voltage and i would at idle as well. I fixed this with a new alt and belt like you have already done and then I upgraded the cables to further increase the efficiency of the system.

    Based on what you are saying in low load situation(on the engine) the system dramatically loses voltage. Usually this would be linked to a bad alt (which you already fixed) or a battery thats gone bad (ditto to before), but from what I can best guess your electrical system has a major thing causing an inefficiency somewhere. Likely it is a random ground somewhere or a short in something that is small enough it hasn't blown a fuse.

    90's GM trucks like ours have grounds everywhere and most of them are on the frame or chassis. I suggest trying to locate any many as you can and cleaning their contacts. Also look for frayed wires, dead bulbs, and fuses that may exist because any of the above may create a problem.

    Also another question. Does this happen no matter what (heavy load and light load) or only when the HVAC blower and headlights and such are on (heavy load)?
  5. E Boyd Daniels

    E Boyd Daniels New Member

    Thanks Conlan

    The AC has no effect on the operation or headlights. I'll look into the grounds, bulbs and fuses. Also think I'll also replace the alternator again with a new one instead of a reman'd one.



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