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Thread: Alternator Overcharging

  1. #1
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    Default Alternator Overcharging

    89 Wrangler; 42.L; no electrical extras. Subject of a previous post and I have done everything suggested but still having a problem so I thought I would recap and see if anyone has any additional diagnostic suggestions.

    While offroad several weeks ago, we got into a tough spot and had to winch. During the process, we burned the positive cable terminal and ruined the positive battery terminal. I am not sure what caused the problem; don't know if the battery terminal was loose; heavy winching. I was also too busy trying to save the Jeep to notice what the voltmeter was doing.

    Was able to get home on the battery only. Replaced battery and positive terminal connection with a military terminal and noticed the overcharging problem. In hindsight, I am not sure if the overcharging problem existed before or after the melt but I had not noticed a problem with the volt gauge before that trip.

    Battery is new and has been checked; also swapped out a battery from another vehicle and same problem. Multimeter shows battery at 12.5-13; turn key on and dash voltmeter gauge only reads 10-11. Starts up easily but multimeter and voltmeter gauge jump to 14 at idle; increase rpms and needle increases to 17. Multimeter confirms 17 volts going to battery.

    Checked, cleaned, and tightened all connections (including connection on firewall); had alternator checked at two parts stores and both say it is good; also replaced alternator belt.

    Before I start buying and replacing parts and pulling the harness wiring out of the plastic sheathing, can anyone suggest an approach and in what order? I have a Haynes manual but it isn't much help.

    Questions:
    1. Is is possible that the alternator is actually bad but reads OK on the test bench?
    2. Why does the dash volt gauge read low when key is first turned on in comparison to the multimeter? Is there anything about the low reading that suggests a place to look?
    3. Read something about the "sense" wire which I believe is the red wire connected to the threaded post on the back of the alternator. Is there anything to test with it that might help?
    4. Read other posts about checking engine codes. If I got the codes, would that help anyone?
    5. Finally, can anyone help me identify the wires going to/from the alternator and from the positive terminal to the firewall?
    Thanks.
    89 Wrangler; 110K miles; 4.2L; 5 speed;

  2. #2
    Registered laybackman's Avatar
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    Mar 2003
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    Default

    Quote Originally Posted by grandlakejeeper View Post
    89 Wrangler; 42.L; no electrical extras. Subject of a previous post and I have done everything suggested but still having a problem so I thought I would recap and see if anyone has any additional diagnostic suggestions.

    While offroad several weeks ago, we got into a tough spot and had to winch. During the process, we burned the positive cable terminal and ruined the positive battery terminal. I am not sure what caused the problem; don't know if the battery terminal was loose; heavy winching. I was also too busy trying to save the Jeep to notice what the voltmeter was doing.

    Was able to get home on the battery only. Replaced battery and positive terminal connection with a military terminal and noticed the overcharging problem. In hindsight, I am not sure if the overcharging problem existed before or after the melt but I had not noticed a problem with the volt gauge before that trip.

    Battery is new and has been checked; also swapped out a battery from another vehicle and same problem. Multimeter shows battery at 12.5-13; turn key on and dash voltmeter gauge only reads 10-11. Starts up easily but multimeter and voltmeter gauge jump to 14 at idle; increase rpms and needle increases to 17. Multimeter confirms 17 volts going to battery.

    Checked, cleaned, and tightened all connections (including connection on firewall); had alternator checked at two parts stores and both say it is good; also replaced alternator belt.

    Before I start buying and replacing parts and pulling the harness wiring out of the plastic sheathing, can anyone suggest an approach and in what order? I have a Haynes manual but it isn't much help.

    Questions:
    1. Is is possible that the alternator is actually bad but reads OK on the test bench?
    2. Why does the dash volt gauge read low when key is first turned on in comparison to the multimeter? Is there anything about the low reading that suggests a place to look?
    3. Read something about the "sense" wire which I believe is the red wire connected to the threaded post on the back of the alternator. Is there anything to test with it that might help?
    4. Read other posts about checking engine codes. If I got the codes, would that help anyone?
    5. Finally, can anyone help me identify the wires going to/from the alternator and from the positive terminal to the firewall?
    Thanks.
    If it has an external voltage regulator it may have fried from all that resistance your corroded + (& -) battery cable caused. If then VR is in the alternator it could still be the problem. It will not satop chargfing the battery even when it is fully charged.
    TC's will not alert you to any charging issues They all relate to fuel/air management and timing.
    I'd rather have a bottle in front of me, than a frontal lobotomy

  3. #3
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    Oct 2001
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    langley, ok, usa
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    Default Don't Rely On Bench Test

    After doing everything everyone suggested including replacing cables, fusible link, and checking and double checking all connections, I decided to buy a new alternator even though two parts starts said my old one was good. Guess what - it was the alternator. When I took the core back, the clerk said that test machines in parts stores do not check every component. Wish I would have known that. I am sure that the alternator failure was the cause of the battery terminal melt and frying of my radio. If 18 volts going to the battery and melting the terminal doesn't cause the fusible link to break, I don't know what will. Anyway, I am back up and running.
    89 Wrangler; 110K miles; 4.2L; 5 speed;

  4. #4
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    Feb 2007
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    Cocoa Florida
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    Default voltmeter guage pegging out

    1998 tj 4 cyl. I replaced my alternator a month ago with new battery and belt, recently the volt meter guage pegged out and I made it home but with a dead battery. I charged the battery cranked it up, volt meter showed the alternator was charging at 14 amps, about 2 miles down the road on my way to the store the voltmeter pegged out. I cannot seem to locate what the issue is any help or suggestions would be appreciated. things I have done so far are check the battery cable connection, test the battery, for some reason the autozone machine will not check the alternator unless you take it out and bring it down.

  5. #5
    Forum Leader LeadFoot's Avatar
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    Default

    Quote Originally Posted by JarheadM198 View Post
    1998 tj 4 cyl. I replaced my alternator a month ago with new battery and belt, recently the volt meter guage pegged out and I made it home but with a dead battery. I charged the battery cranked it up, volt meter showed the alternator was charging at 14 amps, about 2 miles down the road on my way to the store the voltmeter pegged out. I cannot seem to locate what the issue is any help or suggestions would be appreciated. things I have done so far are check the battery cable connection, test the battery, for some reason the autozone machine will not check the alternator unless you take it out and bring it down.

    Then,uh, take it out and have them test it? Reguardless...if you got your alternator from autozone, that would most likely be the problem. Try another alternator from Napa, junkyard, or if you are truly forsaken, the dealer.
    '94 YJ
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