anyone experience this problem before?

[G Fry33]

when im driving at any speed my volt gauge shows roughly 13v but when i come to a complete stop or the cars at idle the volts drop down to the warning level down below 8v. i dont experience any electrical problems but i was wondering if anyone had any ideas about what it could be? it has a new battery and alternator.

[alenstein]

Alternator gremlins

[Craig 94 TA GT]

Yes, it happends to me all the time. It doesn't get to as low as you describe, however, when I have the fan switch on, it will go down to the tip of the yellow/warning area. It does this even with a Powermaster 140A alternator. However, there is nothing wrong with mine at least because I keep my laptop monitoring the systems, and the battery voltage never drops below 12.1. I would suggest, just to make sure, you use Freescan to see the voltage.

[TexasFBody]

Is it making a quick dip, then back up, or does it stay all the way down the whole time the car idles. It is normal for the RPM to drop way down for a quick dip when letting in the clutch at higway speeds or decellerating to a stop, while the computer adjusts the IAC and shuts off the EGR. Most F-bodies will especially dip RPM if you drop the throttle and let the clutch in while cruising on the highway, this is because the EGR valve was open during cruising, and it takes a second for the extra exhust gas to pass through the intake and the IAC to readjust to idle. A drop in voltage and oil pressure will accompany this RPM dip. If your Voltmeter reads constantly low at idle, check the actual charging voltage with a good multimeter. You should test it with your positive lead attached to the junction block under the hood <the one with the red cap on it, next to the fuse/relay block> and your negative probe on the battery (-) or a good ground on the engine. See if this reading compares to what is shown on the cluster.

[94 formula]

Mine did that not long after I bought it almost two years ago. I was planning on replacing the alternator but it quit doing it so I just figured just let well enough alone lol. Also are you the origional owner of the car? Is there any chance someone put underdrive pulleys on it. That could cause the drop.

[Jeff_in_Atl]

Crank the car. Disconnect the battery. Rev it to 1500 rpms. Turn on the lights, hit the high beams, Turn on the rear window defogger, Turn on the heater with the fan on low. Slowly turn the fan up to high. If the car dies, replace the alternator (and regulator built in/on). If not, start checking grounds.

[G Fry33]

i talked to the kid that i bought it from and he said he did put underdrive pulleys on it. so that could be the reason it does that? its one of those things that doesnt really effect the driveability of the car but kind of bugged me.

[94 formula]

Underdrive pulleys would be one of the last modifications I would do. They don't add a whole lot of power and cause issues like that. If it starts to dip when sitting still reving it up should take care of that. With the pulleys its just not spinning the alternator enough at idle.

[G Fry33]

well that makes more sense now. i havent done anything myself for performance parts. Thanks for the info everyone who posted.