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do i have a short ..??

Discussion in 'GM Electrical Tech' started by quicksilver8817, Dec 6, 2012.

  1. quicksilver8817

    quicksilver8817 New Member

    i dont know if this the right section but my truck is having an issue during cold mornings.. my voltage will go up and down up and down for about 10 mins until the truck warms up .. when this happens my fuel pump also whines ... i just upgraded my alternator to a 145 amp(didnt upgrade any wires idk if i should of) but this didnt happen until about 2 weeks after i did that so i dont know if thats realevent .. any help is greatly appreciated ...
  2. RayVoy

    RayVoy Active Member 1000 Posts

    That may be perfectly normal. My old '05 Envoy (AAFAIK all of the GM360/370) had a "cold morning load monitor" built into the PCM.

    When the PCM detected a load condition (engine load from a charging alt) that it didn't like, it would release the alt from charging duties. As the engine warmed, the PCM allowed the alt to charge without interfering. I don't know why it does this (the engine would still have lots of hp to handle the alt charging load), it must be for emission reasons.

    I haven't noticed my Av doing this, but we have only had a couple of cold days and I may have missed it.
  3. quicksilver8817

    quicksilver8817 New Member

    ill take a vidieo tomorrow morning so you guys can see it its almost like something cuts out for a split second repeatedly and it only does it for about 10 min so idk
  4. SurrealOne

    SurrealOne Former Member ROTM Winner 1000 Posts

    OEM wiring should be fine for the alternate, upsized 145amp alternator, by the way...
  5. quicksilver8817

    quicksilver8817 New Member


    its not a great video but i think you guys can kind of get an idea of what im talking about .. any help would be great .. thanks guys ..
  6. quicksilver8817

    quicksilver8817 New Member

    idk if it helps but i just discovered that if i drive it during this time , as i press the gas my voltage drops and when i lay off of the gas it goes back up... help please
  7. RayVoy

    RayVoy Active Member 1000 Posts

    Again, this may be normal, some PCMs will command the alternator to stop charging under WOT conditions. If you were only feathering the gas and it was falling off, then you have a problem.

    A fully charger battery should test around 12.6 volts, an alternator output is usually around 14.4 volts, when charging. If an alternator is switching from a charge state to a no charge start (and the battery is fully charged) a voltmeter should fluctuate between 14.4 to 12.6
  8. This is just a thought, because I want to find out If I maybe got ripped off. When I did my engine swap, I apgraded from a 102 amp alternator up to a 200 amp alternator. I asked the dealer about this, and they said you should have the PCM reflashed to correct voltage spikes that can happen. I fell for it and had it reflashed, It made sense to me at the time. Just curious what your original amperage was on the alternator??
  9. Jamm3r

    Jamm3r New Member

    Tell us more about the upgrade or provide pics.

    If u have an overwound CS130 well that might be enough to explain it as they don't produce as much output at idle as stock.

    If u have an AD244 or a DR44g then it shouldn't do that unless the PCM is telling it to stop charging. It could also be a symptom of early diode failure.

    The stock wiring is 8 gauge which can't carry 145 amps for more than a minute or two without overheating. An upgrade to 6 or 4 gauge welding cable (more flexible) is worthwhile. Some of the better high output alternators have an oversize output terminal to provide better physical support for heavier cable -- the stock stud isn't really heavy enough to support 4 gauge cable properly.
  10. vncj96

    vncj96 New Member 1000 Posts

    You can also use audio power wire to replace the stock stuff, super low resistencia and will be video shielded so you don't get wine through the radio from the engine. Also, is you fuel gauge broken or is your truck empty?? I just ask because if your pump is that loud it's because it's about to go or it's working hard because you have no gas and its cold out.

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