C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette
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Old May 20, 2013 | 09:45 PM
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Almost done with the 70 for the summer (work wise) and I have a nagging little issue I'm always forgetting to ask about on here. Sometimes...but not always...when I turn on my headlights, especially high beams, or AC, the car will act like it is being really taken to task to run them. This is not a vacuum issue I'm sure of it...I can raise the headlights without turning on the lamps themselves and it is fine, likewise the wiper door. Think of anything I can check guys?
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Old May 20, 2013 | 09:59 PM
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bad alternator
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Old May 20, 2013 | 10:03 PM
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Originally Posted by calwldlife
bad alternator
That was my first guess as well, just a little tired. It is the original, and a super rare unit...it's not causing any major problems, so if it is that I will wait till the winter and have it rebuilt.
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Old May 20, 2013 | 10:30 PM
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Both an alternator and AC can put a significant mechanical load on the engine. If the RPM drops slightly when everything is turned on, that's normal.
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Old May 21, 2013 | 09:04 AM
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Originally Posted by Mike Ward
Both an alternator and AC can put a significant mechanical load on the engine. If the RPM drops slightly when everything is turned on, that's normal.
The RPM drops slightly with the lights, and significantly with the AC unless I set the idle to ~900, then it will produce only a slight drop. I like to leave the car set at 800 at idle (spec is 750), because 900 can cause the occasional run-on. No noises or any weirdness from the AC system, and blows cold.
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Old May 21, 2013 | 09:32 AM
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Was there an AC idle solenoid available for '70?
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Old May 21, 2013 | 10:26 AM
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Originally Posted by Brcmpbl
The RPM drops slightly with the lights, and significantly with the AC unless I set the idle to ~900, then it will produce only a slight drop. I like to leave the car set at 800 at idle (spec is 750), because 900 can cause the occasional run-on. No noises or any weirdness from the AC system, and blows cold.
There's nothing wrong with your alternator then.
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Old May 21, 2013 | 11:20 AM
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Originally Posted by Raphiki
Was there an AC idle solenoid available for '70?
No, AIM shows one as planned but cancelled.

Mike, thanks.
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Old May 21, 2013 | 11:26 AM
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Too bad - I could have use that! My '70 has a Vintage Air system but still drops a few RPM when it kicks on. A bit disconcerting when you're idling.
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Old May 31, 2013 | 12:56 AM
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Still haven't figured this one out.
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Old May 31, 2013 | 12:58 AM
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Originally Posted by Raphiki
Too bad - I could have use that! My '70 has a Vintage Air system but still drops a few RPM when it kicks on. A bit disconcerting when you're idling.
I hear you...mine has the stock air compressor, and blows cold, etc., but at idle will pull the RPM down a few hundred easily...like from 800 to 500 or less...with a 4 speed that's no fun in traffic.
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Old May 31, 2013 | 04:10 PM
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Just a thought....
Do you have Pertronics or other after market ignition?
Is it wired correctly to a 12 volt source?
If it's connected to your resister wire it can cause the problem you describe.
Chris
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Old May 31, 2013 | 04:43 PM
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Hi Chris, I still have the stock style points system with the original distributor.

I'm going to check again tonight for any vacuum leaks that could be throwing the idle off a bit, but outside of that I'm at a loss. Idle remains rough with any accessories engaged, but pulls hard in every gear without hesitation.
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