I noticed that my car has started to become slow to kick the starter on so I monitored the volts while driving with my ScanGauge.

Without lights on it reads between 11.3-11.4 and with the lights on it reads 10.9-11.1 volts. Am I in for another alternator?

 

YES !!

If you turn it off it will likely read just a bit higher. A fully charged battery will usually sit at around 12.1-12.4, volts, engine off. Normal voltage while running is about 13.5 to 14.3 This isn't cut in stone but given a couple tenths here and there it's close.
My guess would be that the regulator or diode trio have partially failed.

 

11 volts is no partial failure.

 

If it's not tripping the Alternator, battery light then the alternator is likely still charging some but not putting out what it needs to. The diode trio is what can fail in thirds. If one "arm" goes it will charge at 66% and if two "arms" go it will only have 33% of it's rated ability. It WILL NOT trip the battery idiot light when this happens as that circuit is a very dumb circuit and as long as the alternator is charging at any amount it doesn't see a problem.

There is also a chance there is some corrosion on a connection which is causing the regulator to "see" the wrong reference voltage but I'm guessing Rspi pulled this from a salvage yard and this alternators second life has come to a close

 

Well, I had to take a 30 mile trip this morning about 9 am and the volts was between 13.4 - 13.7. So, I was thinking this is kinda wacky.

Then to church at 11 am and the volts were back down around 11.3.

This afternoon I took another 40 mile trip and on the way back it started to get dark so I turn the head lights on. About 2 minutes later I got on the freeway and noticed that my ABS light came on. I thought, that's strange, this is not a post '95 car and a few seconds later I seen the volts drop to 10.4. Then the SRS light came on and the volts droped to 10.1. Rut ro! I was about 6 miles from home. A few miles later the battery charge light came on and the volts dropped around 9.5 so I reached down and turn off my head lights and continued with my parking lights. The volts slowly dropped to about 8.4. At this time I was about a 1/2 mile from home going down hill. Got stuck at the red light near my place and the volts dropped just under 8. Now the transmission was fishing for the right gear and I hit the gas to get into my apartment complex. Right as I was pulling onto my parking spot the tranny was shifting up and down so I turned the car off, it was at 7.4 volts. About 10 seconds later I reached down to try to restart and it wouldn't even turn over.

So, my guess it that this alternator is dead and I will do as Kiss guessed and head to the junk yard to pull an alternator. This one was in the car when I got it and it usually charged at about 12.4 - 12.7 volts so I have been expecting this for some time. Who knows, maybe I'll find a newish one.

 

The alternator died on me last year without tripping the battery light. The low fuel and service lights started flickering (the gas tank wasn't even close to empty). Then, the wipers were moving slower... and then the radio died, and so did the speedometer (though the other gauges still worked). Then, the car lost acceleration and slowed to a crawl... and stopped moving. Pulled the alternator and had it bench tested. It was indeed dead. Bought a rebuilt one for less than $200 and installed it myself. It's still going strong.

 

Well you need another one or you need to take that one apart and replace the regulator. If it was only charging at 12.4-12.7 it was bad when you put it in. The diode trio is a go, no go part. It's never intermittent but the regulator can do exactly what you describe and give you readings all over the place depending on temperature, vibration and RPM.

 

On modern alternators the module that fails is what the parts guys call the "regulator" but it is composed of:

1. The two brushes and holders
2. The diode pack (typically six diodes; if any one shorts or goes open, you'll have charging problems)
3. and the actual solid-state regulator

When an alt stops working (charging) properly, 90% of the time the brushes just wore out. They usually last about 120K mls or so. That's likely what happened in your case rspi, since they will work intermittently while they're near the end of their rope.


One or more of the diodes failing makes up most of the other failures; probably in the 9% range. Last 1% is regulator, hard wiring failures, or mechanical (bearings).


So unless your alt has more than 200K mls on it, most times replacing the "regulator" assembly will fix it.


There was a time when you could just buy the brushes by themselves from rebuilders but I have not been able to do that for at least a decade or more.

 

I found this video on replacing the alternator, maybe I'll use it to help me figure it out quickly and save time.

The video link was sarcasm. LOL

 

So I go to the yard and pulled the newest looking alternator. Had to stop by AutoZone to pick up something so I had them test it. They said it failed. I typically don't trust their test so I went to Advanced Auto and they could NOT test it. Their computer set-up was wrong. So I went by O'Reilly's and they tested it twice, both times PASSED with flying colors. Their machine said 13.7 was acceptible and it was putting out 14.3. My last alternator usually put out about 12.7 so this will be a treat.

Now to get it in. I'm doing a video. I could get it out in 45 minutes. Hopefully it go in as quick. Raining like crazy here today.

 

Changed the alternator. Took about 2 hours. Easier than expected.