98 electrical issues

I replaced the alternator in my 1998 last July (with much grief) when it began making a bad grinding sound and stopped charging properly. The car still had the original battery as well. So, I decided I might as well change it out at the same time. The battery was from a GM dealer. The alternator was a remanufactured Ultima brand from O'Reilly.

The car would charge fine after the replacement (as high as 15.2 volts). The only weird thing was the tested specs on the new alternator said it would begin charging at 950 rpm. It really didn't start charging until almost 2000 rpm. So, we would have to rev the engine a bit at startup. I really didn't give it much thought.

About 2 weeks ago, I was driving it and it died on me. It started right back up and was fine again. I noticed that it was turning over a bit more before starting as well. The car worked fine until last week. My wife started it up and drove it 2 miles home and it wouldn't charge above 12.5 volts. I checked out the voltage across the battery with a voltmeter and it was 12.2 stopped and 13.0 running. So, it was charging a very small amount. I also noticed that the tach was twitching a bit for the first time. The engine was idling constant. So, it shouldn't have been jumping.

My first guess was that the alternator had went out again. I checked all the connections on the battery, jump post, alternator ground, etc. with no help. I was going to take the car back to O'Reilly to have it checked out as soon as I got the time which ended up being almost a week later. But, now the car won't even turn over.

The battery is reading 12.2 volts still. So, it is not dead. I even tried jump starting it just to make sure with the same result. Something is definitely fried. The instrument panel did flash "Service Vehicle Soon". I also noticed that, when I went to start it, the blower came on even though the controls were saying "OFF". I was curious and turned the controls to defrost and the blower kicked off.

I have no idea even where to begin. It sounds like the computer is fried or something. Any ideas would be welcomed.

Did you reconnect the battery thermister on the positive battery connector?

I have never heard of a battery thermistor.

At your positive battery connection on the positive wire is a round object called a thermistor (temp sensor) it is connected to the loom via a plug. It will regulate the amount of volts that your battery will accept.
Also if your tach was twitching I suggest removing and cleaning the battery connections and all ground wires to the chassis and motor.

I did some reading on the thermistor and it's job and checked to make sure it was connected and it's fuse was good. Which they were. I have cleaned and checked all the electrical connections as well.

This weekend I was able to jump start the car. But, it wouldn't restart. The battery still reads 12.2 volts. So, i don't know if I got a weak battery or the battery is weak because of another bad alternator or another bad electrical connection.

I will probably exchange the battery this week for one that hopefully puts out more than 12.1-12.2 volts and see if it will start and charge to 15.2. If not, I will probably exchange the alternator before I kill another battery.

Well, I ended up taking the alternator off Saturday morning and took it to O'Reilly to get tested. It was bad. I asked them if they have had a problem before with this "Ultima" brand alternator. I am debating on whether or not to spend $135 for an upgrade to an AC Delco brand. Has anyone out there had a bad experience with either brand? The good news is it only took me 3 hours to take the part off this time instead of 6. Maybe next time will only be 1...