Battery gauge

Discussion in 'General Tech' started by tm8004, Jun 5, 2015.

  1. tm8004

    tm8004 New Member

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    Maybe this question is dumb but I'm pretty bad with electrical issues
    I have 94 gt and the battery gauge seems to be at 1/3 of the way up only and goes lower while driving
    I bought a new battery since my alternator died on me a week ago so I bought a new one
    then a few days later my battery dies so I just bought a new one
    I thought my gauge would go up since its new but still didn't
    could it be that the battery isn't charging?
    Also the dash doesn't light up when I turn on the lights it's pretty bad in the dark
    is this a battery issue too?
     
  2. ttocs

    ttocs Legend

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    could be a couple of bad grounds but the stock voltage gauge isn't all that accurate. Your not running under drive pullies are you
     
  3. RichV

    RichV Well-Known Member

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    Not sure what 1/3 of the way up is, but you should be at 12v with engine off. 14-14.5v with engine running. You can test this with a meter, or they sell a voltage gauge/display that plugs into the power outlet if you want.

    I know the gauge cluster is what tells the alternator to charge, so if something is not working there it may be causing your issue.

    Easy way to test, start engine and remove positive terminal from the battery. If it stays running, the alternator is charging. If not, you have a charging issue.
     
  4. evilcw311

    evilcw311 Most Evil Mod! Staff Member Staff

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    Not necessarily true on efi cars. That was an old way of testing back on carb'd cars. Lost of efi cars will instantly die if you undo the battery.


    This message courtesy of crapatalk!
     
  5. RichV

    RichV Well-Known Member

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    Explain to me why a EFI car would die and a carbed car would not. I can go do this right now with my 94 and I GUARANTEE it will stay running.
     
  6. RichV

    RichV Well-Known Member

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    I'm bored, so I just did this on my 05 GT. Let's take a look ...
    [video=youtube;M8VGJ5Z-dC4]https://www.youtube.com/watch?v=M8VGJ5Z-dC4[/video]

    In all fairness, IIRC there are cars out there that have a sensor on the battery, and if it's sensed missing it will turn off. Maybe some of the Mechanics on here know more about the latest technology.
     
  7. GregT94SCC

    GregT94SCC New Member

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    Its actually bad for the electronics in the car to pull the battery while running.

    I think my 94 has an idiot light as well as the voltmeter. The idiot light bulb is part of the charging circuit. I don't think the gauge is part of that equation.
     
  8. rz5.0

    rz5.0 Legend

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    That's the old school way of checking alternators.. That's not a good way now in days.. It's a good way to damage your alternator and/or ecc...
     
  9. rz5.0

    rz5.0 Legend

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    Just use a volt meter...
     
  10. RichV

    RichV Well-Known Member

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    OK, explain to me why.
     
  11. csellis3842

    csellis3842 New Member

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    My electrical is in tip top shape and when im idleing at a redline with ckutch in or in netural my gauge is at the n or o but if i rev it up or take off it goes to normal most of the time when im cruising im at the m mark.
     
  12. RichV

    RichV Well-Known Member

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    Yes, the charge light (not really the light but it is a part of the circuit that tells the alternator to charge). I had to jumper 2 wires in the cluster connectors to get my setup to charge.
     
  13. rz5.0

    rz5.0 Legend

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    Im not good at explaining stuff and I'm not an expert. But the battery connected gelps ground spikes. With the battery disconnected those spikes can damage electronics..
     
  14. mcglsr2

    mcglsr2 Well-Known Member SN95 Supporter

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    The issue could be several things:
    a) bad alternator,
    b) alternator is good but not charging battery

    You can easily find this out using a multimeter (if you don't have one, spend some money for a decent one [like $50 or more], it's a good investment).

    Step 1) With the car off, battery connected, measure the voltage across the battery terminals. Voltage should be around 12V (a tad below is fine). If the voltage is a lot below 12, like 11.4 or lower, then the battery needs to be charged.
    Step 2) With the car running, battery connected, again measure the voltage across the battery terminals. The battery is now being charged by the alternator so the voltage measured should be around 14V. If it is too high (like 16V) the voltage regulator in the alt is shot, alt needs to be replaced. If the voltage is too low, it's because either 2.1) the alternator is bad or 2.2) the charging circuit is faulty, so the alternator is not being told to turn on.

    The best way to tell if the issue is 2.1 or 2.2 is to take the alternator to a shop like Auto Zone or Advanced Auto and have them test it. If they test it and say it's good, then your issue is 2.2 - charging circuit. I am familiar with this circuit and will be happy to walk you through troubleshooting it. If they say the alternator is bad, then replace it. You may also need to put your battery on a charger - the alternator canNOT recover a battery that has been deeply discharged.

    To answer the question on why disconnecting the battery from an EFI car *might* be bad: the battery in this EFI system is used as a sort of buffer - if there are any surges or spikes, the battery absorbs it rather than delicate electronics. The reality, though, is that the alternator (and it's voltage regulator) is what is really controlling the voltage, surges and spikes. So, the battery should be able to be disconnected from this system with no problem. On a car that is running normally and fine, then yes the battery can be disconnected. Shouldn't matter. However, if something goes wrong (for example a master cut-off switch is hit) and the voltage all of a sudden has no where to go (because there is no battery and no specific ground provided for this situation), then it will most likely ground out through delicate electronics, typically destroying them in the process. A carb car is not as susceptible as it doesn't have the delicate electronics. On an EFI car, with a properly designed charging system, removing the battery shouldn't cause an issue (though cars now may have sensors for this), though I wouldn't recommend doing this too often or for too long. Also, some cars actually measure the temperature of the battery to help determine certain things (like injector pulsewidths) but this is typically in startup conditions and not running conditions).
     
  15. RichV

    RichV Well-Known Member

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    I think the battery is something to keep constant load on the alternator, rather than a ground connection. The chassis is the ground, battery is just connected to it.

    Since the alternator is actually making AC power, then through a rectifier bridge converting to DC, the problem could be the alternator's regulator/DC converter is not working. Then when the battery is disconnected, the AC influx can damage the electronics. This is possible, my SVO alternator had a diode disconnect once which would make the DC a little funky, but no damage was done.

    I agree on getting the alternator tested regardless. However, whenever mine died, I've always checked by pulling the positive battery lead and results have been 100%.