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  1. #1
    New Member VetVette's Avatar
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    Default Charging question

    So a couple weeks ago I bought an 85 with 23,000 miles. Tonight I had the voltage meter on instead of coolant temp. Long story short is that while idling in park, the voltage is fine. But if I'm stopped at a traffic light, I can watch the voltage get lower and lower. Car seems to idle around 600 in park and around 560-570 without the A/C on.

    Am I looking at possibly needing a new alternator? Can I adjust the idle a little higher? What are your thoughts? Thanks.

  2. #2
    Member LLC5's Avatar
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    Quote Originally Posted by VetVette View Post
    So a couple weeks ago I bought an 85 with 23,000 miles. Tonight I had the voltage meter on instead of coolant temp. Long story short is that while idling in park, the voltage is fine. But if I'm stopped at a traffic light, I can watch the voltage get lower and lower. Car seems to idle around 600 in park and around 560-570 without the A/C on.

    Am I looking at possibly needing a new alternator? Can I adjust the idle a little higher? What are your thoughts? Thanks.



    Make sure that the battery cables are clean and tight ,and have your battery properly load tested with a carbon pile tester, not a theoretical electrical tester, if the battery is bad or on it's way out the voltage can be low. But basically you need to perform the voltage test at the battery clamps with a quality voltmeter, gauges are not always accurate.
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  3. #3
    Member Hot Rod Roy's Avatar
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    Quote Originally Posted by VetVette View Post
    Long story short is that while idling in park, the voltage is fine. But if I'm stopped at a traffic light, I can watch the voltage get lower and lower.
    This may be normal as the battery recovers its charge after starting the engine. You say "voltage is fine". What voltage are you seeing? Check the voltage at the battery terminals with an accurate volt meter while the engine is running. Do you see the same voltage decrease? Do you see a different voltage if you test the output of the alternator (alternator red wire to battery neg. post.)? Do you have any extra accessories in the car (i.e. super stereo)?


  4. #4
    Member DonB's Avatar
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    Make sure the ground cable is making a good connection where it meets the block, too. Also, I Can't remember off hand right now(if the '85 has this), but check for the ground junction at the left, lower, rear of the engine by the trans. and make sure the connections are clean & tight. It may have NO effect on your issue, but it'll cause a ton of freaky things if NOT cared for.

    Checking at the battery(or the hot pole on) the alternator it should put out about 13.5 volts when running. If the battery is down or bad the alt. can put out up to around 15VDC.
    Last edited by DonB; 05-28-17 at 08:54 PM.

  5. #5
    New Member VetVette's Avatar
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    Thanks guys. I meant to check it out some this weekend, but the weather was so nice I had the top off and was cruisin'. Plus I cleaned out the lean to next to the garage to park it under.


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  6. #6
    Member Vettehead Mikey's Avatar
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    Quote Originally Posted by VetVette View Post
    So a couple weeks ago I bought an 85 with 23,000 miles. Tonight I had the voltage meter on instead of coolant temp. Long story short is that while idling in park, the voltage is fine. But if I'm stopped at a traffic light, I can watch the voltage get lower and lower. Car seems to idle around 600 in park and around 560-570 without the A/C on.
    If you didn't look at the gauge, what other symptoms are there?

  7. #7
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    Quote Originally Posted by LLC5 View Post
    gauges are not always accurate.
    Well said and that is the difference between a gauge (approximate) and a gage (accurate).
    Whoosh, and blur

  8. #8
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    I had the same problem with my 1990. Replaced my alternator and everything works great.

  9. #9
    New Member VetVette's Avatar
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    Quote Originally Posted by Vettehead Mikey View Post
    If you didn't look at the gauge, what other symptoms are there?
    Didn't really notice anything until I looked at the gauge.

  10. #10
    Member Vettehead Mikey's Avatar
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    Quote Originally Posted by VetVette View Post
    Didn't really notice anything until I looked at the gauge.
    Then if the battery is maintaining a charge and the alternator is putting out reasonable voltage while driving, I'd stop looking at the gauge.

  11. #11
    New Member VetVette's Avatar
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    Quote Originally Posted by Vettehead Mikey View Post
    Then if the battery is maintaining a charge and the alternator is putting out reasonable voltage while driving, I'd stop looking at the gauge.
    Probably a good idea Charging question

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