I've had this problem for a while, and i'm trying to diagnose it. The voltage drops into the red while idling, and only when the car is at running temp. If I give it a little gas while at the light, the indicator will move up. In other words, when I get the alternator spinning a bit more, it puts out the right amount of voltage. Is there any way to fix this so that the indicator doesn't drop into the red when i'm idling? Its not the battery. I changed it not too long ago with a yellow top optima. The battery before was a red top that was like 4-5 years old and it died after leaving it a week without starting.

 

Have you tried getting the alternator checked to make sure it is fine? I would also make sure that your belt is not slipping.

 

Same problem here. Alternator's good, battery's good, belt's good, just a gremlin somewhere...

 

There seems to be a fine line as to what rpms alternator charging voltage drops off. Your particular alternator may just be a little wimpier at low rpms than the next one.

 

Here's the deal. I just double checked everything on my way home. At ~600 rpms, the voltage dipps, touching the red part of the guage. If I give it a slight amount of gas to ~750-800, its back in the middle. Any ideas?

 

Are you sure the car doesn't have an underdrive pulley. It slips in behind the harmonic balancer.
After I put the pulley in it does just that.

 

I'm positive. It wasn't doing this before.

 

If it was not doing it before, it is probably the voltage regulator in the alternator that is getting tired. Either that or you have a new, big drain on the system that you did not have before.

 

Thanks for the help guys. I guess i'll just keep chugging away until the alternator dies.

 

Do you guys with the low voltage at idle have an U/D pulley?

 

yup, I have the alt od pulley also and the lights dim at idle in drive. But it's not too bad so I don't worry about it.

 

I just have a wimpy U/D pulley and it dims my lights to the point of annoyance at idle...I'm about to tug it back out and sell it

 

My voltage always drops a little but I figure its from the car having its oriiginal alternator from 93.

 

Would stepping up the alternator to somewhere around 200W be a good idea? ...or maybe even have it rebuilt to support more watts? I'm also running a stereo system off of everything and didn't really want to get a capacitor...

 

Yes, you can have the original rebuilt. Alternators are rated in AMPERAGE, not wattage. I would reccommend getting it rebuilt to higher specs, and getting a capacitor. Your just placing too much drain on the battery and the charging system with out one. (if you have anywhere near a strong audio system.)