Symptoms of a failing alternator? What is going on?

Hi All, I'm trying to figure out what is going on with my '99 C2. Recently, I tried to start it after a week and a half of not driving it. It was dead. Click click click. Charged the battery back up, starts no problem. Drove around. Next day, dead again. Jumped it, drove it for an hour, and all seems fine. The battery gauge shows just a hair under 14 when driving it. After the drive, 10 mins go by, and the car won't start again. Battery is dead. The weird thing to me is that while driving, the gauge keeps showing it is near 14. Hmmm… Went and had the battery tested at the auto parts store, and they say it is good. The battery is only about a year and half old. So am I looking at an alternator going out? Or is it out? Could I drive a full hour on a bad alternator? Not sure of the next step(s) I should take. I'm not to savvy when it comes to the electrical side of things. Any help appreciated. Thanks!!! CR

Here's a good generic alternator test procedure using a multimeter. http://easyautodiagnostics.com/alter...ic_tests_1.php Also, most auto parts stores have an alternator tester that will load up the alternator and check output.

Its pretty easy to take out the alternator. Much easier the second time though. It could be the voltage regulator (which is on the alternator) which is easy to fix and a lot less expensive then replacing the entire alternator. The other thing to check for is corrosion of the alternator cable at the starter as well as the ground strap from the engine to the body of the car. The below links may help: http://www.renntech.org/forums/topic...tage/?p=240055 http://www.renntech.org/forums/topic...trap-location/ http://www.renntech.org/forums/topic...tage-problems/

when you had the battery tested at your local auto parts store, did they also do a "load test" for the alternator?

Thank you guys for the help thus far. I did t know they could test the alternator as well. I'll have to look into it. It may be time for me to get a multimeter of my own. Kromdom, they did do a load test. He had to charge the battery a little bit (it was reading 12 when I took it in). Then he tested and said it was good. Any other advice is appreciated. Thanks!

Have them load test the alternator (my local O'Reilly's does it for free) so you'll know for sure if you need a new one . Best of luck.

If you turn on the low beam, a/c and rear defroster when the car is moving, the gauge should read 13-13.5v. If it's below, most likely your alternator or some cables are bad. Also, in the morning when you put the key in to the last position before crank, the gauge should read 12v and when you crank, it should read 10v or more. If your numbers are lower even after you fully charged your battery, it's likely you have a bad battery.

If the battery went dead after just a week and a half of sitting that's hardly the fault of the alternator. That's the fault of a bad battery. If the alternator wasn't working no way the battery could supply the juice to keep the engine running for an hour. More on the order of a few minutes, at best.

I smell bad battery, or bad cabling. Those "battery tests" have been wrong before. 14v whilst operating sounds like a good alternator.

Cables....

I think its a battery issue. A dead battery won't be charged by the alternator in an hour. Properly charge up hour battery with a charger and see what happens. You might have something draining it or a bad cell.

My guess is something is drawing power from the battery when the ignition is off that shouldn't. I'd check voltage right after turning the car off, then again 1/2 hour later.

Check this thread http://www.renntech.org/forums/topic...tage-problems/ Look at post #9 and #13 That crossover wire from the alt to the crimp at the starter has a bad habit of corroding and causing charging/starting problem.

I had an alternator that tested ok running, but with the engine off would put a large drain on the battery. Must of been an internal short as the alternator was quite warm to the touch when the car had been sitting overnight.

Thanks everyone. I'll check some things you've mentioned this weekend. I'm hoping its a battery or cables and not the alternator. I'll let you know what I come up with. Thanks again!

Thanks everyone. I'll check some things you've mentioned this weekend. I'm hoping its a battery or cables and not the alternator. I'll let you know what I come up with. Thanks again!

UPDATE: Looks like the battery was in fact bad. Had it tested at a different auto parts store, they said it was dead (had even last voltage just sitting on my workbench for two days). Took it back to the original place and they tested it again and confirmed, this time, that it was bad. Warranty in place, got a free battery. Will hook it all up tomorrow and hopefully all will be well. After a week of not driving the 911, I'm having withdrawals! Can't wait to drive tomorrow. Thanks for all of your help! Rennlist rocks! CR

I am having an interesting problem with alternator/charging system in my 2002 Porsche 911 and was hoping someone here can help. The alternator is Bosch remanufactured unit that I installed ~10k miles ago. Here is the operation. If I start the engine cold, everything works fine and system voltage goes to ~13.8 - 14 volts immediately upon starting and stays there as it should. You would never know there is any problem with the system in this scenario. However, when starting a fully warmed up engine, the alternator does not turn on initially. I've let it idle for several minutes after a hot startup, and voltage with remain at ~12v (so running on the battery) without the alternator turning on and with the battery/alternator error. The system will continue to run off the battery until I rev it to around 1,500 - 2,000 rpm as shown in the video. Once I hit this RPM level, the alternator turns on, as you can see the voltage goes up to the proper level, and then the alternator output remains normal (~13.8v) regardless of the RPM, even if it goes back to idle. So the issue appears to be that for some reason the alternator is not turning on when hot and at idle unless I raise the RPM briefly. However, it has no problem supplying sufficient voltage at idle even at high electrical load once it actually turns on. Appreciate any thoughts/feedback on what may be causing this. Here is a video: https://www.youtube.com/watch?v=cNq0...ature=youtu.be

There are likely two things (1) your Y-cable needs to be replaced; (2) after 10K on a re-manned unit, your alternator is getting heat soaked and the voltage regulator is failing. Replace the Y-cable and put in a brand spanking new Bosch alternator. Not re-manned, NEW.