[Parenn911]

I just got home from Whole Foods, and saw the red alternator light come on and hear a buzzing whirring sound coming from my engine. I suspect my alternator may be failing, thoughts?

[88carrera]

Plug wires going bad? The sound though may be loose drive belt or belt starting to shred.

[Vicegrip]

Don't Internet guess, test.

[Trak Ratt]

^ agreed, but if the idiot light comes and the engine isn't overheating then IMO it's a pretty good guess!

[Parenn911]

Originally Posted by Vicegrip

Don't Internet guess, test.

Originally Posted by Trak Ratt

^ agreed, but if the idiot light comes and the engine isn't overheating then IMO it's a pretty good guess!

True dat! Any information on what is the best test to perform, any special tools I will need?

[Vicegrip]

Brain, hands, eyes, ears, voltmeter. Use eyes to see that everything looks OK and in place. Check belt tension. Check that battery conections are clean and snug.

Set volt meter to DC volts and in a voltage range where 14 volts is mid scale. Start car. Test voltage at the battery while car is at idle and at 3500 rpm. Does voltage go to 14.7 or better at 3500? Listen to the alt and belt. Look and sound normal?

If no increase in voltage there is a list of next steps starting with checking the conectors at the starter and then the back of the alt.

[cmartin]

Good idea. Also check the battery with engine off, then add some load like headlight and/or fan and check again. A dead battery or dirty connection has sold many alternators.

[Vicegrip]

Run lights for a min or two before checking battery. A bad one can still hold an ok surface charge. Running the lights strippes this off

[blipshift]

If you don't have a voltmeter take the car to autozone and they can hook a machine up to your car and tell you what electrical systems are failing. Then while you're there, buy a voltmeter

[Dr K]

Originally Posted by threedownandlocked

Then while you're there, buy a voltmeter

Good advice!