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Discussion Starter #1
Have an old AND a new alternator both exhibiting the same symptom; a very loud whining noise when running, as opposed to the clacking noise of bad bearings and such.

The new one actually tested good on AutoZone tester, but failed after reinstalling it. If battery cable is removed, car dies instantly.

The noise will change when the plastic connector is removed, but it does not go away. I saw this video :

youtube dot com/watch?v=hmPUUVwIJUU

and this is my issue EXACTLY.

Man in video states the diodes being bad is cause of noise. I can only assume he is knowledgable.

Battery has good charge. Parasitic drain on battery is about 600mA when car is turned off.

Does anyone have any ideas what could cause an alternator to do this? I am STUMPED!!

Thanks in advance for your attention.
 

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Sup Mod keeping the peace
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If both the old and the new alternator are producing the same characteristic whine, then there may be a problem with the wiring. A properly working charging system puts out about 13.2 to 15.0 volts, but this is a general spec. and the factory service manual (FSM) should be referenced for the correct charging system voltage specifications for a particular vehicle. A battery should have a static charge of 12.2-12.6 volts. If a battery is not good, the charging system may not be able to charge properly. If a vehicle is not charging properly and the battery is good, first thing to do is to turn the ignition switch key to the "ON" position and make sure the charging system warning light is operating. If the bulb is burnt out, the charging system will not charge. If the bulb is OK but still does not illuminate, the circuit must be tested. If the warning lamp does illuminate, then the next thing to check is to make sure the circuit between the battery positive post, or fusible link, to the connection in back of the alternator is good. On Nissans, this will be a thick (approx. 10 gauge) white wire to the "BAT" post on the back of the alternator. It's not uncommon for this wire to get corroded and burn up, creating resistance in the circuit. So, before assuming an alternator is bad, make sure this circuit is good and battery voltage is getting to the alternator. It's also important to make sure the alternator belt is tight and not slipping and the battery connections are clean and tight. Also, it is NOT a good idea to disconnect a battery cable on a computer controlled vehicle while running to test the alternator. This is a good way to damage an ECU. When a charging system is not charging, or overcharging, a lot of "strange" things can occur.
 

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Discussion Starter #3
Thanks for the reply. Is there anywhere online that I might find a wiring schematic for this model. Tried googling, but just other models instead. Will have to look for service manual I guess.
 

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NF Mod/Nissan Master Tech
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600 milliamps is way to high for parasitic draw; it should be no more than 50 milliamps. Remove the 10 gauge wire to the "BAT" connection on the back of the alternator and see if the parasitic draw drops; also make sure everything is turned off and doors are closed when checking the parasitic draw. If the draw drops down to below 50 milliamps, then the alternator is causing the draw. These alternators have an internal clutch assembly for the pulley that often fails on the original units. Don't be surprised if your replacement alternator is bad as aftermarket remans can be very unreliable. Your best bet for a replacement alternator is using a genuine Nissan reman alternator. One more note: you should really have posted in the L31 Altima section, as this section is meant for only the Altima SE-R. It's no big deal, but you may get better exposure and/or a quicker answer when you post in the proper section. Good luck with your Altima!
 

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