I put on an UD pully and Ive knowticed the alt gauge in the car gets really low. When I start the car its fine, but when it gets up to temp it drops down to the 13 on the gauge.
I checked the battery and the alternator.
Battery with car off--> 12.57
Alternator at start up--> 14.38
5 min after start up--> 14.05
A couple min later--> 13.95
Is this caused by the pully or is my alt going bad? And I do have a sub/amp but I tested this with them off.

 

Yes, you need to install a larger pulley for the alternator now, to allow it to catch up to proper rotation speed....

 

I found these at SUMMIT. Which one of these do I need? How big is the stock pulley?

 

Edit: Did a better search and found a link. Hopfully a new pulley will fix the problem.

 

There is ZERO problem with your alternator or pulley. 13.95V at idle is perfect...nothing to worry about. I don't even begin to worry about a charging problem until you are dipping below 13V. Anything above 12.8V is considered charging.

 

Sorry, I just realized that I kinda touched on this in the first message but didnt elaborate. I only tested the volts with the car sitting there idleing. When Im driving it sometimes drops below 13 volts. It gets low enough that my amp turns off. (forgot to mention that)

 

If it's dropping when the RPM is up, then it's a bad alternator. The problem with underdrive pulleys is that they lower the rotational speed of the alt, making them charge less at idle when the RPM is low, but as you get off idle, the alternator spins faster and it charges again. If it charges at idle and drops off, you probably have a bad regulator that dies as it heats up and the alternator needs to be replaced.

 

What happens is when I come to a stop it drops down. I can put it into neutral and it goes from below the 13 to between the 13 and the next line. Also while Im moving it is between the 13 and the next line.
I figured Id spend 20 bucks and hope it fixes it, instead of just jumping and buying a new alternator. Someone stole my "money tree" out back , so I didnt want to spend a lot of money.