Voltage woes

Shop says the charging system checks out fine. The wife commands I replace both the battery and the alternator. Sigh.....

2 possibilities: 1. Alternator is intermittent. 2. A short exists somewhere that is loading down the system, but not enough to blow a fuse/let the smoke out.

If you wait long enough, either the alternator will go from intermittent to permanently not working or the smoke will be let out of the wires somewhere. Either way, momma gets stranded and you will NEVER HEAR THE END OF IT.

In reply to Dr. Hess:

Indeed. I really think the alternator is to blame. If it was a short it would have to be a huge one to create that sort of voltage drop, so I think the smoke would have already been released.

Time to roll up my sleeves.

Edit: apparently my wife made the executive decision to have the shop replace the alternator. Good bye $170 for labor. Sleeves returned to their normal position.

Guess it was the battery. The voltage was still fluctuating with the new alternator. I had the battery tested, no bueno. Seems rock solid with a new one.

Also which ever GM engineer came up with the 8mm screw on battery terminal deserves to have his testicles gnawed on by a rabbid honey badger.

In reply to bgkast:

Why? They solve a lot of issues with the post style batteries. I've never had a corrosion issue with one(cause the battery isn't as prone to cracking and leaking), they're harder to overtighten, and easier to clamp to. Also a lot harder to accidentally set a wrench on them.

The threads are bigger than the bolt head, the head rounds off because the metal is softer than cheese, and it binds in the terminal just enough so that you can't start it by hand.

Maybe it's just the awful position of the negative terminal in this engine bay, buried way back under the fender.

Glad to hear you had that fixed... If momma is not happy, no one is happy..

Some stores have a battery/alt tester that doesn't require removing anything. It also doesn't require any smarts. Its an electronic box that you hook to the battery. You press a button and it says things like start engine, turn on lights, turn off engine, turn off lights... it measures voltage drops and then at the end it says "replace xxxxxx."

But, a healthy alternator should provide over 14v at idle. Even with everything running at once, it shouldn't ever drop below about 13.5v. Industry standard is 14.6-14.7v for alternator output.

I can't explain why it was doing what it was. Maybe the battery had an intermittent internal short.

Dang, still doing it. With the healthy battery when it drops it only goes down to 12v. No loss of power any more either. I'm thinking maybe a bad connection to the alternator? Any reason why the ecm would be cycling the alternator on and off?

In reply to bgkast:

Could be a goofy ECM, got a old 1 wire style GM alternator on the shelf or know somebody you can borrow one from?

I forgot the the voltage regulator is built into the alternator in this vehicle. It's a 2 wire alternator, and it's brand new, so unless it failed exactly like the old one it's not the issue. Off to study wiring diagrams.