My alternator will be working fine, 13.8 to 14.1 volts with or without a load on it. Then I see the dash flicker and the voltage is down to 12.6 or so, depending on the load. Sometimes it starts charging again, sometimes I'm lucky to make it home before the battery dies. Took it to Autozone and it tested good. Rather fix it than buy a new one, but don't want to throw parts in it and still have trouble. Any ideas?

 

Probably the voltage regulator inside, and never trust those idiots at Autozone. They said mine was perfect, then I replaced it, and had no further problems.

 

They are not idiots; they are just using a tool to test the alternator. Electrical components may perform differently when HOT (as in an engine compartment) than when bench tested. Since the Auto Zone guys/girls are not getting paid to trouble shoot your problem they will tell you it passed since it passes on the tester and move on to the next customer. If you need troubleshooting and want a repair performed correctly; you are probably going to have to do it yourself or pay big money since competent, knowledgeable, people are compensated at rates much higher than minimum wage.

Its probably the Alternator, check for loose/corroded connections and when you don’t find one install a new/rebuilt alternator.

Good luck.

Mike

 

What aboatguy said! I agree 100%!!!

also, Autozone is selling a new brand, Duragold, of NEW alternators. These seem like very nice parts. Installed one in bastet44s 87 and it works PERFECTLY. Has a damned good warrantee, too. All for 129.00!!!

 

My symptoms sounded exactly like yours...
Fortunately it dropped to 11.9V just as I pulled into Autozone. They tested it and found I had a "bad diode pattern"
$6 for the new diodes. Working fine now.

 

Maybe you dont have billybob redneck running the tester in your town, but this guy told me it was perfect, and that my starter was bad.

Because apparently he runs muscle cars and has infinite experience with everything GM

 

If the alternator quits charging the battery, the red battery symbol on the dash will light! Does it? When your dash voltmeter drops into the 12's, the alternator is not charging the battery and you can pull over, leave the engine idle and measure the voltage on the output terminal of the alternator. It should be 14.7 alternator cold, to 13.7 hot. If the alternator measures 13.7 to 14.7 volts and the battery terminal voltage measures much less than the alternator output, you have a bad connection from the alternator to the battery and you need to check the terminal lug on the alternator output wire, the fusible link in the output wire and the lug and connection quality on the end of the alternator wire near the battery (on my 87 its the jump start terminal behind the battery). Wiggle the alternator output wire on each end and at the fusible link and watch for the battery voltage to jump according to flexing the wire. Also check the quality of the plug in connector into the alternator, if the plug pins are corroded or have low spring tension, this might be your source of trouble. Next, the alternator may also be intermittent, and more so when hot. Parts houses don't test the alternator at various rpm, nor at elevated temperatures.

 

The most common, but not the only, reason for this is bad diodes.

 

I agree with Vader. These morons should NOT be saying an alt. is great due to the tools they are using. It obviously was an intermittent problem that they didn't diagnosis correctly.
I've had the same problem at work with a certain printing press that has had an intermittent problem that I told the press operator I couldn't fix it until it acted up when I was there to see it. I never told him what the problem was (or wasn't) until this past Friday and it screwed up with me there. I did a few quick checks and found the problem.