I have a 1980 Z28 with a charging problem. It has a new battery, starter, solenoid and alternator. I recently found the power lead to my distributer had been downsized from 12 ga to a 16 ga wire. I replaced this section and it charged fine, 14.4 volts. Or so I thought. I have now noticed that at cruizing speeds the alternator doesn't keep up with the load and I lose voltage. At idle it starts coming back up as long as the battery is still charged. Before I bought the car someone installed an Accel HEI supercoil distributor. I'm wondering if my standard alternator with a 63A output just doesn't keep up with my load? I have tried removing fuses one at a time and there is no change. I have turned on everything in the car with the ignition off and my voltage drop at the battery in only .2 - .4 volts. Once I start the car and bring the RPM's up around 2k, I show a steady drop. There is no one accessory that causes a quicker drop in voltage. I have also checked the drive belt on the alternator, it's tight. All connections and grounds are good and clean. I have traced and checked all wires from the battery to the starter, alternator and fuse block. Replaced the alternator plug and solenoid fusable links.

Any help would be greatly appreciated.

 

Welcome to the site!

Have the alternator tested. Sometimes even new ones don't work right.

 

I agree with having the alternator tested. Welcome to the site.

 

Welcome! The guys that posted above me are smart; you should follow their advice.

 

Thanks for the advice and friendly welcome.

I had my original alternator tested 5 times, always tested good. I thought I'd try a new one anyway in case one of the diodes had gone bad and the test didn't show it.

I did however fix the problem. I added a 10 ga wire from the battery to the back of the alternator and tightened the s#!t out of the belt. That seemed to do the trick. The belt seemed tight before but must have slipped enough at higher RPM's to stop charging. It seems to me like the belt is overtightened now but it's working correctly and if I loosten it at all it doesn't charge as well.

 

That seems indicative of another problem to me. Could a bracket or something be bent, such that you don't have the correct range of adjustment for the belt tension? I'm not terribly familiar with your car/engine, so I can't really be specific.

 

Bench testing alternators isn't always correct. I am thinking that there is a belt issue, because the alternator should charge at higher rpm's vs. idle, sometimes to low of an idle alternators won't start charging until rpm's come up.