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Alternator Issue

TiTAN

By TiTAN,
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TiTAN Grand Master

TiTAN

Posted
Posted

two days ago the battery light came on in my car. Checked the voltage and it looked like the car was running on the battery only. I have just installed a replacement alternator and the issue is still there that the battery light is on and the car isnt making more than 12v.

If you run the car with the jumper leads connected to another running car it idles/revs fine if you disconnect it the fuel pressure drops and the car leans out (i assume thats to do with voltage)

do you think i have gotten a faulty altternator or is there some other electrical issue that people know of that would stop the alternator making any current?

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mad082 Grand Master

mad082

Posted
Posted

could it be a battery issue where the battery is what is stopping it from increasing the voltage?

there is a way to check this although it isn't the best thing to do. start the car with the battery connected, then disconnect the battery and check the voltage of the alternator then connect the battery again. only problem is that there is a small chance that the extra voltage from the alternator can damage the ecu, but i have seen this done before when jump starting a car without jumper leads.

Bozz Proficient

Bozz

Posted
Posted (edited)
  mad082 said:
could it be a battery issue where the battery is what is stopping it from increasing the voltage?

there is a way to check this although it isn't the best thing to do. start the car with the battery connected, then disconnect the battery and check the voltage of the alternator then connect the battery again. only problem is that there is a small chance that the extra voltage from the alternator can damage the ecu, but i have seen this done before when jump starting a car without jumper leads.

Do not do this. Easily possible to destroy all electronics on your car and cost you a lot of money in repairs. That was an old trick before cars had electronics, to test if the alternator was working. The battery acts as a large capacitor and supresses voltage surges through the electrical system. Most EFI cars have enough of an idle current draw to keep a regulated alternator from spiking sharply but do you really want to chance it? Have you ever tried to switch on cruise control while your driven wheels were in the air? The reg in the alternator behaves very similar. Massive over and undershoots without the battery attached.

Nissan alternators needs 2 things to properly charge a battery. A voltage reference input and an excite wire. The VRef wire should be attached to the battery positive to measure how much voltage drop there is in the charge wire, to keep the battery fully charged. The excite wire provides a tiny amount of current though the charge light to energize the alternator as it contains no magnets. The excite wire is clearly working (white / red stripe) so check you have 12v on the other wire (i forget the color) on the 2 pin connector.

edit - the white/red wire should be close to zero volts with the engine off, then up to 12v with it running. The other wire on thta connector should have 12v on it all the time.

If the white/red wire still has close to zero volts with the engine running and the other wire has 12v, you have a faulty alternator.

Edited by Bozz
DRD-00F Grand Master

DRD-00F

Posted
Posted

yeah I would have guessed that...

I've had the battery terminals drop off the batery a few times (the negative) and nothing went wrong, besides a quick drop in voltage whenever I turned the lights on... But my alternator is in pretty good nick, I have no plans of needing to change it anytime soon...

The positive terminal hasn't come off since I put the new battery in there about 2 years ago...

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