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2G Is my alternator bad?

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bo0st

10+ Year Contributor
835
22
Jan 26, 2010
Phoenix, Arizona
Sometimes my AEM volt gauge will display 7v and at other times it’s displaying 12-13.

FYI: I’m unsure if this alternator was ever replaced. The battery itself is a brand new red top optima which is testing well

also if it helps I could upload a log from link
 
Sometimes my AEM volt gauge will display 7v and at other times it’s displaying 12-13.

FYI: I’m unsure if this alternator was ever replaced. The battery itself is a brand new red top optima which is testing well

also if it helps I could upload a log from link
Haved you tested the battery voltage with a volt meter when the cars idling?Id start there
 
Sometimes my AEM volt gauge will display 7v and at other times it’s displaying 12-13.

FYI: I’m unsure if this alternator was ever replaced. The battery itself is a brand new red top optima which is testing well

also if it helps I could upload a log from link

My car idling, volt gauge says 13.5. Have you checked the generator relay ( which isnt a relay)? Do you have a ground strap on your alternator? Battery is in the factory location?
 
If your system voltage is dropping to 7v in your log as well I'd check the condition of your battery too.

2G's ECU will turn off the alternator output to reduce the engine load and improve emissions but it shouldn't let the voltage drop that low and the car can run quite a while with no charge before the battery goes that dead.

Lets see the log, it will give more clues.
 
My car idling, volt gauge says 13.5. Have you checked the generator relay ( which isnt a relay)? Do you have a ground strap on your alternator? Battery is in the factory location?

Hey there, thanks for the quick reply! I haven't checked the generator relay yet and I didn't look closely enough at the alternator to notice a ground strap. The battery is indeed in the factory location.

If your system voltage is dropping to 7v in your log as well I'd check the condition of your battery too.

2G's ECU will turn off the alternator output to reduce the engine load and improve emissions but it shouldn't let the voltage drop that low and the car can run quite a while with no charge before the battery goes that dead.

Lets see the log, it will give more clues.

Thanks for the quick reply Steve! It's a brand new battery so I don't believe that's the issue.

I may have been a little too late in turning on the laptop, I don't think this log has any drops below 13V but let me know if you see anything that would point to a bad alternator:
 

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Hey there, thanks for the quick reply! I haven't checked the generator relay yet and I didn't look closely enough at the alternator to notice a ground strap. The battery is indeed in the factory location.

I personally dont have a ground strap on my alternator. But I have read people adding one to help with voltage drop. The log looks fairly normal to me. But Ill let someone else speak on that part. Im assuming you checked for loose wires? I would measure the volts at the battery and the alternator to confirm what you gauge is saying. If your alternator measures 7v when your gauge says, I would double check everything in that circuit. But I personally never had a alternator that was bad intermittently. They always just died on me without notice.
 
Does your dash battery light go on when the key is first turned on? A burned out light (and bad/missing generator relay) will prevent alternator field coil voltage and so the alt won't charge the battery.
 
I personally never had a alternator that was bad intermittently. They always just died on me without notice.
The normal ground path is via the bolts holding the alternator and those holding the bracket to the block and from there via the main block ground cable back to the battery. Just think about all the rust and crud that can get in the way. Installing an alternator ground seems like a really good/cheap way to improve the performance of the electrical system.

My original alternator in the 1G lasted long enough for the brushes to wear out. The electrical system did some interesting and sometimes exciting things when the brushes would arc.
 
Does your dash battery light go on when the key is first turned on? A burned out light (and bad/missing generator relay) will prevent alternator field coil voltage and so the alt won't charge the battery.
Typically no but the light will come on after. Here is a new log and in this one I noticed quite a bit of fluctuation. I turned the car off/on a few times for testing purposes.
 

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I noticed that my gauge says 13.6 but ECMlink will report different values so I’m unsure which one to trust.
 
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