Hey guys I have recently developed a new problem in the 81. It seems that one minute the alternator is charging the battery and the next minute it is not.

The volt gauge will randomly drop from 14.2v to <12v while the car is running. This happens regardless of whether it is idling or if I'm cruising down the road. The needle will drop to less than 12v for a some time and then shoot back up to normal voltage. I only drove it a few miles in fear that the battery may run out of juice and cut out on me.

The alternator is a cs144 which I installed about a year ago along with a new battery. During the install I also added an extra 4 gauge wire from the alternator to the starter post in parallel with the stock one.

The gen light does not come on when the voltage drops while driving.

So far I've checked the connections at the battery posts, the battery ground, the starter post, and tightened the connections at the alternator but so far I have not been able to find a solution. The belt is not slipping either. I also poked around with a voltmeter earlier today to make sure it wasn't just the gauge going crazy on me.

I got the alternator and battery tested at the local auto store but I'm not ruling out the possibility of a bad alternator since the problem seems intermittent.

 

Is there a way to determine if its a bad voltage regulator or rectifier diode?

 

I suspect that the terminal connections on the wires plugged onto the alternator are corroded and intermittantly allow the alternator to 'charge' or 'not charge'. Remove the plug, then clean the pins on the alternator AND the terminals in the plug. Then reassemble and try it again.

P.S. It would be best to pull a battery wire, first. One of the wires in that plug will be 'hot', otherwise.

 

Thank you for the help, I fixed the problem.

I opened up the alternator and found that the nut holding the BAT post inside the alt had managed to work itself loose. There were some black spots on the heat sink near the nut, probably caused by arcing from the bad connection. I cleaned up the terminals and tightened everything down.

I put it all back together and it is charging normally again

 

These rebuilt alternators... Replaced my original one because it was giving me similar symptoms to yours. Few months down the road while working on the engine I noticed the main screws holding the damn thing together were lose (the long ones holding the two halves together). Even when you get new parts you still have to worry about them!

 

The one in the car is a remanufactured Ultima alternator. Unfortunately cheap china parts are getting harder to avoid these days.