Pull Pwr1

Hello,

Got a question about the Charging System on my 1997 S-10 Blazer. My Amp Guage normally stays around 14 volts when the engine is running. Now the guage is fluctuating between 12 & 14 volts. Is my alternator going bad or do I have a battery problem?

It does this on and off no matter if I'm turning on something that puts a load on the system or not.

It does not matter how long the engine has been running. It will stay steady at 14 volts then all of a sudden drop to 12 and then back to 14 etc,,etc.

Thanks in advance for your help.
Pull Pwr1

Siliconasp

I would suppect that the battery has begun to fail due to age. As it the case with automotive batteries, you should replace them every 5 years, whether they are showing issue or not. I would suppect that you have a cell or 2, in the battery that is going out.

Easy test.

Start Truck
turn on AC, Radio and Headlights if so eguiped
let engine come to temp (about 2 to 4 minutes)
remove the POSITIVE battery cable.

Results.

Engine Dies - replace the alternator
Engine is running - lights dim - replace the alternator
Engine is running - no noticeable change in lights - replace the battery

out of car testing of battery

using external charger, charge battery to full, attach multimeter to battery and check voltage and amp. note this. repeat this test every hour for 3 hours. if you notice more then a .5 voltage drop then the battery is bad and should be replaced. If not change seen, check all cables from Alternator to battery for looseness.

Pull Pwr1

Thanks very much for the information Siliconasp! I'll make the test and see how it works out. I was told the built in voltage regulator in the alternator was bad by a friend who has mechanical experience,,,I suppose it could be checked either way by the test your telling me about.

I replaced the alternator with a new one yesterday before I new about the test and it is still doing the same thing.

Thanks again for your time.

chaser

If you replaced the Alternator and it’s still not working correctly I would just suggest getting a new battery as well. You can take the batt to either Wal Mart or AutoZone and see if they will test it. They will check to see if any of the cells are bad or I it’s not pulling the right amount of cranking amps. Not sure if the voltage regulator would cause the problem but you can take it off clean the back of it with a steel brush and make sure its good and flush against the truck.

Not 100% but you can’t do the above test on most vehicles because it will shut down no matter what pretty sure it tried it on a 92 Chevy I had and I wouldn’t work I cant remember the reason but its sort of like a failsafe but you can give it a try.