losing volts

[wad_e]

my 98 z28 loses volts at around 2000 rpm's took the alternator off had it checked, it passed. the battery is good, but after driving around awhile it kills the battery. all connections look good, i dont think it has underdrive pulleys all looks stock, anyone have any ideas?

[pajeff02]

There could be a problem that when the alternator gets hot that something causes it not to charge. This would explain why it passed the parts store test, but does not charge on your vehicle. Try using an analog or digital voltmeter to test your battery voltage with the vehicle off (and engine cold) as compared to running. Test again after the vehicle warms up and see if there is any difference. Interesting dilemma...

[mark21742]

seriously have it checked one more time on the car and them one more time off the car. three times so far (on multipul cars) ive had them test good, then later findout it was the alt the whole time