I hope someone can help me here. Im new to the z28 after wanting one since 93. Now i have a 97 that needs serious help. Anyways to my problem at hand. After owning the car for about a week i noticed the battery gauge dropping out. I decided since i wanted to make this car nice again i would just change battery and alternator. I got a belt as well. First thing i noticed was the belt was too long. Lucky I could read the #s off the old one, and so i bought the new right size belt. I figure something is diff to needed that new smaller belt. Well everything seemed great but I noticed that now when i start the car it idles at around 100 rpm. the batt. gauge stays around 14ish. as i drive it stays 14 ish, But as soon as i come to a stop light it drops to about 11 volts. I used my multi meter and read the same volts so i assume the gauge is right. Im wondering if anyone has a starting point for me to start trouble shooting. thanks in advance..

 

Take a look at the crank pulley. The previous owner may have installed an under drive pull set which slows down all the accessories. The consequence of this is lower voltage output at idle...

 

That would also make sense as to why the other belt was too long. Are you sure the car is idling at 100 rpm? Did you mean around 1000 rpm?

 

Does the belt tensioner hold good pressure on the belt? Have you cleaned all the connections and grounds? Good idea even if it isn't causing issues.

 

sorry i meant 1000rpm. the pully does seem small. not sure if its underdrive or not. if thats the case then maybe it could be it if its normal for underdrive pullys to hurt voltage at idle? just gets me the car does fine until i put it in drive, and idle.

 

Check your battery cable between the alternator and the battery. It could be corroded or damaged. I had a similar problem, my battery voltage would drop below 8 volts randomly when I drove.

 

For me, neg battery cable loosen up from the battery itself not firmly clamped.

For me I see 14 when cold, then after awhile driving drop to 12, idle would be a normal 11 after warmed up and battery charged.