I put my car back together and went out on Friday night, only to find my voltage reading very low at night with the lights on. My battery had been sitting for the majority of the winter as I intended of buying a new one in the spring, so I suspected it to be the culprit. I knew the battery was near death given the car had struggled to crank over. But I was excited to drive my car after six months of waiting, so I went ahead despite the poor battery. Anyway, after noticing my driving lights getting dimmer when the brakes were applied, then returning to normal. I looked at the commander to see voltage dropping to 11.8 under breaking. Obviously way too low.

So the next day I went out and bought a new battery (800 cranking amps) to see if this would resolve the problem. At idle the voltage is around 14.0-14.1, and when the lights are turned on (brights as well) and the brakes are fully depressed the voltage stays at about 13.6. However, while driving under hard braking with the lights on (again brights as well) my voltage dropped to 12.8 on a few occasions. I believe I did the test about 5 times, with the voltage staying at 13.5-13.6 the other times.

I searched but I couldn't find any good information about low voltage other than Yanni's thread about 4-6 months ago. I’m also running the Greddy alternator/WP, and I know they reduce overall voltage. But I was wondering, are readings of 12.8 under full load too low even with the Greddy pullies?

 

I have underdrive pullies and I still see 14's... with the occasional 13.8 or 13.9 ..... possibly your alternator needs a rebuild?

 

is your system grounded well? i dont' know if this would make a difference or not

 

Common problem with Greddy pullies. Best combination is stock alt. pulley and Greddy water pulley to keep the belt from slipping. If battery dies, alt could be at fault but rare.

 

thanks guys anyone else?

 

Since you bought a new battery, I suggest you...

Check you alternator connections
Re-ground your car
Have your alternator checked at Kragen(for free)

I also saw lower voltages from running underdrive pullies.