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Q: Alternator overproduces power above roughly 5,000 RPM, how badly do I need to replace it? Worst case scenario?

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2000 nissan Maxima, 165,000 miles Bought a used alternator around 150,000 miles

Basically pretty much only when I floor it (which is more often than your average driver for me haha) any electronics will go overboard for anywhere from a half-second to about two seconds tops. This includes the fans blowing harder, and the lights getting brighter mainly, and two lights will come on in the dash. It is fairly reproduce-able and not random. Could the ECU crash eventually?? : /

The alternator should not be putting more than 15.5 volts and 95 amps at 5000 RPMs. If the alternator is, then you need to replace the voltage regulator inside the alternator or replace the alternator. Make sure you have a battery that is fully charged and is good when tested with a load tester. If you continue to run the engine with the alternator above the 15.5 volts maximum (should be about 13.5 volts normally), then you may burn out components and it will cost you much more than a replacement alternator will. The ECU and other modules have protection for over voltage, but this protection may not provide long-term protection against voltage above the 15.5 volts may eventually burn out. I recommend having your electrical system inspected by technician, such as one from YourMechanic. They will be able to make a diagnosis and replace your voltage regulator or alternator if necessary.

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