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Dec 1, 2010
05 vette charging at 12 volts when idling in gear, replaced alternator and same thing. any ideas? 6l automatic,
In gear it's idling quite low, normally about 500 rpm's : not exactly the optimum charging time. I'm thinking around 12 volts could be normal.

Question: Does the charge rate rise to the normal 14 - 14.5 volts at cruising speed, and is the battery holding a charge? -- A load test would tell a lot.

Something to keep in mind is that our precious 'vettes do have a lot of live circuits that could cause excessive discharge and discharge problems do seem to be quite common.

If it were mine I'd want to know if there is excessive discharge with engine off and that the new alternator's charge rate is within spec.
A voltmeter is all you need.
ok, a little more time to tell here. it started dropping voltage with the old alternator. it was ok at 1000 rpm but drops to 11.5 volts in gear at idle. changed out 2 new alternators, and the pulleys to attempt to bring the voltage up. with the new one, it charges at 13.5-14, then as it sits in gear it slowly drops to 12.5 then eventually to about 11.5. tested battery and load everything is good and replaced the battery last august. and it is fine as well. my local mechanic says it may need a pcm reflash, what the general consensus here.
May just be a bad battery even tho it's not very old.
Suggestion: try another battery (that you know is good) from another vehicle to see if it acts the same or the problem goes away.
That would at least eliminate the battery as a source of problems.

No need to worry about fitment since all you need do is connect and let it idle.

Are you sure there's no excessive voltage drop as from a short circuit or a light being left on? (engine off).

so I have turned up the rpm in gear to 700-750 and the charge stays at 14 volts, also turned up neutral idle to 85o rpm, works ok now. I just have to be more aware, but no real noticeable difference when sitting at a red light, for foot pressure on the brake that is.

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