Hi Everyone:

I'm trying to determine if i'm getting the proper voltage in my car. My car is basically stock except for a downpipe. When i'm sitting at the light (in gear) with load(radio, popup lights, gauge lights, and turbo timer) my voltage readings is between 12.8 - 13.2 (according to the turbo timer) and drops a little and recovers a little. Sometimes it gets lower and the dash lights dim a bit. I searched for what is the proper voltage, but most of the information I've found refers to people that have the underdrive pulleys in there FD. I already re-did the grounds by adding a ground strap from the negetive terminal to the upper strut tower, alternator to the strut tower, and UIM to chassis. So could anyone tell me what is the proper voltage and also where should I begin searching for fixes.

 

Regulated voltage from the alternator is 14.1 to 14.7 volts (temperature dependent, hotter the lower). With the stock pulleys this would be above 2500-3000 rpm and with zero electrical load. (source '94 FSM)

As there is always a load on the system, a voltage of 13.1 to 13.5 v would be considered normal at running rpms, dropping down towards idle.

You can consider alternator output as being proportional to rpm up to a preset limit set by the regulator.

 

For future reference, the Factory Service Manual specifies these values.

 

Your cooling fans may also be running as you sit at the stoplight. Those motors draw a lot, but the ECU compensates by kicking up the idle speed a bit.

The battery is intended to supply power mostly for starting the engine, while the alternator supplies power to operate the engine and accessories once you are under way, plus it recharges the battery for the next start.

If your meter is accurate and hooked up correctly, you may be drawing down the battery when the voltage is below 13.2 V.