Alternator problem? Battery issue?
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Posting Guru
Joined: Oct 2005
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From: CA
Alternator problem? Battery issue?
For some reason, my battery light comes on when I rev the engine or when I take off. What does it indicate? Alternator problem? The indicator light goes away as soon as I bring to idle or stop at traffic. Any thoughts?
Post Fiend
Joined: Nov 2001
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From: Tallassee, ALabama
Check the tensioner to make sure if is still in good condition. On the old V belt motors, if the alternator belt wasn't tighten properly it would not charge the battery. Sometimes the lamp would light, sometimes not.
Posting Guru
Joined: Jun 2012
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next step is a voltmeter so you can see what the alternator is actually doing when the light is on. I wouldn't fully trust the OBDII output to a scangauge for this, the drop may be too transient for it to be captured with that setup.
Brian
Brian
Senior User
Joined: Apr 2011
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From: Southern Oregon
Mine was doing that while towing and hit higher rpm's. Found out the brushes were almost gone and the stator was ruined on account of that. New alternator and problem is gone. Old alternator lasted 13 years.
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Posting Guru
Joined: Oct 2005
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From: CA
Thanks guys,
Here is the voltage reading that I was able to pull out last night.
#1 running ( high Rev or Low Rev): the cable output at the battery:
Passenger side battery: 12.1v, Driver side Battery 12.13 Volts
#2 Not running battery output @ terminal:
Passenger side: 12.23 and Driver side: 12.24 Volts.
The in-cab voltmeter shows 14 Volts however!
Questions:
#1 Does the alternator charge system connect to both batteries? or is a single charging cable that splits to both?
#2 The belt is fine however I will replace it now (it has lasted 14 years and so is the alternator).
#3 The batteries are about 5-6 years old, with the voltage reading above in non running state, do you think I should replace them as well?
Here is the voltage reading that I was able to pull out last night.
#1 running ( high Rev or Low Rev): the cable output at the battery:
Passenger side battery: 12.1v, Driver side Battery 12.13 Volts
#2 Not running battery output @ terminal:
Passenger side: 12.23 and Driver side: 12.24 Volts.
The in-cab voltmeter shows 14 Volts however!
Questions:
#1 Does the alternator charge system connect to both batteries? or is a single charging cable that splits to both?
#2 The belt is fine however I will replace it now (it has lasted 14 years and so is the alternator).
#3 The batteries are about 5-6 years old, with the voltage reading above in non running state, do you think I should replace them as well?
Postmaster
Joined: Sep 2010
Posts: 3,472
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From: Southern Cal
You are not getting any charge to your batteries. You should expect to see 13.8-14.2 volts while running. 12.7-12.9 static.
Mine truck is a little newer but my alternator line hooks up to the passenger battery, however, both get charged as a direct connect. I would expect both batteries to be almost exactly the same voltage when running when alternator is charging properly.
Not sure what your gauge shows, vom at the batteries is the best way to check.
You batteries, based on such low voltage can't be determined if bad if the system has drawn on them with a bad alternator. Even though pretty old, get a new alternator and also top charge both batteries with a good amperage charger first.
Once that's done, vom the batteries again. Wait a couple of days and compare.
Mine truck is a little newer but my alternator line hooks up to the passenger battery, however, both get charged as a direct connect. I would expect both batteries to be almost exactly the same voltage when running when alternator is charging properly.
Not sure what your gauge shows, vom at the batteries is the best way to check.
You batteries, based on such low voltage can't be determined if bad if the system has drawn on them with a bad alternator. Even though pretty old, get a new alternator and also top charge both batteries with a good amperage charger first.
Once that's done, vom the batteries again. Wait a couple of days and compare.
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Posting Guru
Joined: Oct 2005
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From: CA
ok, one more question: What brand of alternator to buy? I ask this because there are some brands pepboyzzz and 0-Really carry that are pretty much useless unless you know what to look for.
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Postmaster
Joined: Sep 2010
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From: Southern Cal
Some really good info from Bullitt if you take the time.
https://www.ford-trucks.com/forums/1...o-replace.html
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Posting Guru
Joined: Oct 2005
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From: CA
Hello guys, the alternators at pepboyz and 00-Really is rated at 105 Amps??? what did I miss. Reading all the threads attached, I see people are buying 130,140 and hell one guy mentioned 170 Amps. What I'm I missing here?
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