Hi everyone. I bought a used 2010 G37x Sedan about two months ago. When I purchased it, it was running great. In the last month or so, I unfortunately have had multiple issues pop up.
About a week ago, I had a CEL come on. I don't have a scanner, and it was the weekend, so I had to wait until I could get with my step-brother to check it out with his scanner. I was assuming it was an emissions code popping up, I had a few of them already which I'm pretty sure was related to the gas cap. Replaced that, Haven't had one for quite a while now though. My car still seemed to run fine.

That evening, my accelerator pedal suddenly stopped working (thankfully, in a parking lot), and I sort of rolled awkwardly out of the way a little bit. After restarting my car, it stalled, and wouldn't start again. I had no power.
Got towed home, charged up the battery, and the car started up and worked fine again, but the battery wasn't being charged and was just depleting.

Ordered a replacement alternator, and had it installed on Friday. CEL turned off. Since then, though, the car starts and runs fine, hovering at around 14-14.5v with A/C off, and the battery rests at about 12.4v while the car is off.
However, when I activate my A/C, the voltage drops to around 12.95-13.2 and jumps around within that range. I can hear the car almost struggling as if it's about to stall, but it doesn't, it stays alive, and still drives fine.
I can see my headlights pulsing, and my RPMs seem to go up and down, with the lights pulsing to match. Turning off the A/C does not restore the voltage, and this behavior continues until I restart my car. After restarting, it holds at 14.5v again and everything seems fine, until I engage the A/C.


Could the replacement alternator that I got bad? Could the battery be struggling? Is the A/C Compressor getting seized, and is the car struggling to crank it? I just find it weird that I hadn't noticed this issue at all before, until my car died and my alternator was replaced.

Any insight or ideas is appreciated - my wallet is starting to grow thin!
Cheers.

 

Always check codes before throwing parts at a unknown problem. It may/ may not have been the alternator, but being you replaced it there is no way to know now. My first though would have been the battery current sensor, but... too late now.

Where did you buy the alternator and, if you know, what brand?

Check the video out in this thread. If your interior lights are also "pulsing" then you likely have a bad alternator. Yes, even "new" (or, "refurbished") alternators can be bad.

AC draws a lot of current to function. The radiator/ condenser fans turn on, the cabin blower, the various modules to regulate the refrigerant and temperature circuits- it all adds up. To me your description of that symptom appears normal.

Even though the electrics on these cars are highly durable, the electronics are extremely sensitive to voltage changes which explains most of your symptoms.

 

Appreciate the response! I purchased it from RockAuto. It was a remanufactured alternator, I believe the brand was BBB Industries. Seemed to have decent reviews from what I could see. It does have a 30 day warranty that fully but that sure doesn't help the labour costs.

From what I have seen, the interior lights/dash all work fine even while the headlights are pulsing. I will need to do more testing on the dome lights and everything though tonight to be sure.

I tried charging my battery last night with my charger. It was reading 13.1v. when I disconnected the charger. I turned the headlights on to discharge it and it immediately dropped back down to 12.4v.

Car seems to run fine with a/c, radio, seat heaters and everything off, although when I checked the voltage when I got home it was at 13.2 (while idling) - going to try replacing the battery to see if by some miracle that helps somehow, and if not, I'll return it and see about getting that alternator exchanged for a different one.

Thanks for your time mate

 

In almost every case whenever there is pulsing, or flickering, of the lights that varies with engine rpm and load, the alternator is suspect. Some folks here have reported issues with Chinese units sold on Rockauto as opposed to the Hitachi or Mitsubishi OEM units. While I understand the need to "penny pinch" sometimes the aggravation is not worth the cost difference.

Temporarily, you could disconnect the battery current sensor and see if that changes any of these odd behaviours keeping in mind doing so "may" set a code itself.

Additionally, as added confidence, make sure ALL of the electric connections are clean, tight, and dry.

 

I can't explain the why or how, but replacing the battery seems to have done the trick. I did clean the connector terminals pretty well too and made sure they were good and tight on the new battery.
Under full load (A/C on, headlights/fogs on, radio full blast), it maintains 14.4-14.5v, and all seems well - no more sputtering sounds and no more feeling like it's going to stall. Thank God.

One thing I noticed when taking the old battery out is that whoever last replaced it put the incorrect battery group in and had it propped up with a chunk of wooden plank so it would reach higher.