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voltage change all the time


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Which car?  You may have a PCM controlled alternator.

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2006 tacoma stock alt  bought a new one stock. doesnt do this all the time. also at a light no music playing it drop down slowly sometimes. from 14.7 to 13.9  sometime 

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Your alternator is probably PCM controlled.  The computer may vary your alt output based on a number of factors.  Damn near everyone with a newer car has to deal with this issue.  There are modules out on the market, but not for every make and model.  

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On 8/11/2017 at 7:07 AM, WalledSonic said:

Your alternator is probably PCM controlled.  The computer may vary your alt output based on a number of factors.  Damn near everyone with a newer car has to deal with this issue.  There are modules out on the market, but not for every make and model.  

That is the best answer you're going to get. 

My car used to do it when I had my stock alt. The PCM would down my voltage when I would idle at lights. Drop from 14.0 to 13.3. You're on the lucky end of the spectrum. Your voltage is high for a stock alt. 

I just replaced my alt with a HO one about an hour ago and hot it reads 14.4. So you're reading higher than me and I have an aftermarket alt thats not even PCM controlled anymore. 

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I am seeing this with 2 different brand self exciting alts. NOT computer controlled ( from 14.7 to 13.9 ).
what I did notice is that when a load is being applied the stay level, even a constant RPM levels them out.

I wont list the brands right now. Both are hairpin self exciting and I think both have an LRC of 2.5 or 5.
not sure if it has something to do with self exciting regulators.

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I wouldn't worry about .3 or .4 volts. There are a lot of things that need power in a car that might turn in or off. This will change the load the alternator sees. Like radiator fans power steering pumps and power brakes (maybe). Differences in ambient temperature will play a role in alternator cooling which will effect output.

Does any one get a rock solid 14.7v all the time?

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