I isntalled a high output alt in my 2002 I35(vq35), and now my car only seems to charge at 13.5-13.8 volts.

I kept factory wiring, but added on 0/1 gauge in several locations, 1 run of wire from the alt to the positive post of the battery, 1 run from the alt casing to the right strut tower, and one run from the battery - to the left strut tower, all the ground are secure and sanded clean. I am wondering if voltage is controlled via a pcm or something to that effect...I need to be charging in the 14's not the mid 13's. any help is greatly appreciated!

 

You are right about the voltages, 13.5 is low. Specification is 14.1 to 14.7 volts.

The voltage is controlled by a small printed circuit board inside the alternator, referred to as the voltage regulator. They are not adjustable.

The extra wiring you did does not sound like it is incorrect. Depending on the amperage output of the alternator, it might not have been necessary. Even if unnecessary, it is not harmful.

The only thing that could cause low voltage other than the alternator being bad would be that there is more demand for electrical current than the alternator is capable of providing.

So if the car is essentially stock with no outrageous sound system and lots of extra lights, I would say the alternator is bad.

 

FSM States

Regulated output voltage 14.1 - 14.7V

If you replace stock wire with thicker larger wire, keep in mind you have a lot more media to deliver power. If your not using more, you should not expand your capacity and may have a negative effect. Your alternator was use to a normal strain, now it has to work harder to provide same required power level. Your alt may have been fine before but if it works harder now it may go out sooner. Getting a new one should condition it to your current wiring and you should not have any issues. Voltage is regulated on the voltage regulator in the alternator. Stay away from ebay alternators and claimed high output ...