What would cause an alternator to stop charging for a split second intermittently?

Forum for Infiniti M35 and M45, and Nissan Fuga owners.
eyedeekay
Posts: 21
Joined: Tue May 21, 2019 6:14 pm
Car: 2006 Infiniti m35

What would cause an alternator to stop charging for a split second intermittently?

Postby eyedeekay » Sun Oct 25, 2020 12:03 pm

2006 infiniti m35

So I replaced a reman alternator because I was having this issue where the rpm would randomly drop at idle. When I got an identical reman to replace that one, the same issue occured. I know for sure it's alternator/ electrical related because I got a used one from a donor car temporarily and the rpm did not fluctuate like this.

Therefore I ran some tests with my voltmeter and it seems like the alternator for a split second stops charging to battery, as the the voltage drops from the normal 14.6 to to 12.6 volts at idle. Curiously, 12.6 volts is the voltage of the battery when the car is OFF and battery is charged.

Things I verified already:

Alternator ground and plug are secure
Battery terminals are secure
Battery terminals were replaced
Battery was replaced
All visible ground wires were cleaned
Tension on serpentine belt is firm.


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Ilya
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Car: 2011 M56x but I spend a lot of time on my 2015 Kawasaki Vulcan S. Former owner of a 2007 M35x. Also take care of my wife's 2016 QX60.
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Re: What would cause an alternator to stop charging for a split second intermittently?

Postby Ilya » Tue Oct 27, 2020 5:44 am

That's an odd one...maybe some sort of lose fusible link somewhere? Does the FSM have any troubleshooting steps for the alternator?

eyedeekay
Posts: 21
Joined: Tue May 21, 2019 6:14 pm
Car: 2006 Infiniti m35

Re: What would cause an alternator to stop charging for a split second intermittently?

Postby eyedeekay » Thu Oct 29, 2020 6:29 am

Ilya wrote:
Tue Oct 27, 2020 5:44 am
That's an odd one...maybe some sort of lose fusible link somewhere? Does the FSM have any troubleshooting steps for the alternator?
I think I determined the issue. The reman alternator overcharges the battery higher than the stock alternator. My obdii app shows the reman alternator charging upwards to 15.1 volts. For reference the stock alternator never went above 14.6 volts and should operate at 14.3-14.4 volts in most cases. In order to compensate for the higher voltage the batterg receiving, the ecu cuts power received from the alternator to prevent overcharging of the battery.

Also, as far as why the stock alternator failed on me, it was mostly likely from a very fast power steering fluid leak from the pump which I replaced.

As for why the alternator is overcharging, I think it's not the alternator failing but rather how they are remanufactured from factory. Keep in mind this is my second alternator from the same exact retailer (NAPA) and the this same issue occured in my first example. Maybe the factory who rebuilds them are not making them provide voltages similar to factory, or the regulators are worse than factory.

I guess this is for anyone who is looking to replace their alternator for their M car, but if you experience weird idle fluctuating a it's most likely the ecu cutting power from the alternator to prevent overcharging of the battey

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Ilya
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Joined: Fri Apr 23, 2010 11:20 pm
Car: 2011 M56x but I spend a lot of time on my 2015 Kawasaki Vulcan S. Former owner of a 2007 M35x. Also take care of my wife's 2016 QX60.
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Re: What would cause an alternator to stop charging for a split second intermittently?

Postby Ilya » Thu Oct 29, 2020 10:05 am

Thanks for sharing! Definitely sounds like what's going on.


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