Joel5.0

Yes it affects performance, you can check its output with a VOM to be sure it's an alternator problem, or get it bench tested free at any big chain auto parts store.

Fox

Using a voltmeter, check across the battery terminals with the engine running and you should read approximately 13.8 volts. This is the alternator output.

philly3384

with no accessories on im getting 12.4

with accessories im getting 11.6

Fox

Sounds like your alternator is bad. You should be able to run headlights radio etc. without much voltage drop. 13.8 is a regulated voltage out of the alternator.
Now if you have a voltage regulator seperate from your alt. then the voltage regulator could be bad, but most late model cars have the regulator built into the alternator.

Put the negative lead on a good ground anywhere on the chassis (Bare Metal), and the positve lead on the + side of the battery, but put it on the cable connector itself. You should read 13.8 Approx. If not I would suspect the alternator.

ckyguy68

are you running underdrive pullies?

philly3384

no underdrive pullies