I am having a small issue with the charging system in my 99 coupe. Not a huge deal really but it does drive me a bit nuts. For some reason the charging voltage will drop from 14.1 or so down to 12.6 (battery voltage) and back quickly. It's just long enough for the lights to blink slightly dim. If it wasn't for that I wouldn't even notice it. I have verified with my meter that it does drop so I am not just going off of the DIC readout. I have checked cables from alternator to battery and can't find a voltage drop. I have cleaned the grounds.

As for my alternator, there is no tag or information on it. I bought the car with 138k on the clock and based on looks it has been there a while. I did open it up and found that it had the Valeo Regulator and brushes so I replaced those thinking that might be the issue. No change.

The problem seems to happen more often when there is more load on the alternator such as the blower on high or the lights on. Rolling the windows up or down will cause the voltage to fluctuate but not drop that low.

I know the PCM sends a "turn on" signal to the alternator. Could this be dropping out and causing a problem? The car has been doing this since I bought it so who knows how long it has been an issue.

 

The first thing I would suspect would be the regulator, but you have already replaced it, is it possible that the alternator output current rating might be to low for your car?

 

It is possible. I wish I had a way to test it and know. No markings on the outside of the alternator itself. Would it be possible for the ignition switch to have this effect? I was thinking of taking it apart and cleaning it just to eliminate that as a variable.

 

Ignition switch's can cause many problems, but I have never heard of it causing charging system problems, most auto parts stores can test alternators if you remove it and take it in, they might help you find out what model it is.

 

Did you check the charging wire? The connection at the alternator and the fusible link and connection at the solenoid.

The PCM can't turn off the alternator once it's excited and charging.

 

This is how my battery voltage and currentdraw from my battery appear when I start my car .
Voltage drops from 12.9 volt to approx. 9 volt the first 1/10 of a second when the starter current is maximum .
After approx 1 sec it increase to 12.5 volt and after 8 seconds the voltage stabilize at 14.3 volts
Orange curve(A) is battery voltage
Green curve(B) is starter current (amp clamp with 1mV=1Amp)

 

I didn’t think it could but wasn’t 100% sure. I did check the connection at the alternator and cleaned it. Did not check the connection at the fuseible link. I will check those next.