C4 Voltmeter

The battery on my 84 was low and I charged it. When I started the car the dash voltmeter read 10.8 volts. I had the alternator checked and it put out 14+ volts. I check the ground cables from the battery and
they are OK. I checked the volts at the battery without the engine running and it read 12.3 volts, and 14.4 volts with the engine running. Anyone got any ideas?
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How old is the battery? Sounds like it needs to go.

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puked:

Isn't 14v a couple volts low? -- lab~rat >:-) Do you want polite or do you want sincere?
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richk55 wrote:

voltmeter and with a voltmeter at the battery. Leave it for a few hours then recheck. If the voltage has dropped below 11 your battery is probably toast. You can also do a load test by simply turning on your headlights (car not running) and check the voltage drop periodically. You can also check the charging system the same way by running the car with everything electrical turned on and see if the alternator output drops.
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richk55 wrote:

I'd not worry too much. 10.8 isn't too bad a "sag" when cranking. When it gets below 10 then I start shopping for a new battery. If it drops to 9, I immediately buy a new battery. Somewhere down below 9 volts during cranking, the engine electronics will start to misbehave. At 8 volts things go to hell in a handbasket--and most L98s will quickly run the battery dead on following a "sag" to 8 volts.
Another real cold snap and you might have an issue but I'd guess you'll make it through spring and summer.
After the engine has started, the voltage at the alternator and battery should range from 13.5 up to 14.5 volts. The dash should agree with that give or take .75 volt. Although the C4 dash instrumentation was pretty good, we're not talking NASA grade stuff here.
Alternator output voltage when running is a real crapshoot. The alternator re-builders are using after market regulators. (This is a good deal because the new stuff is much better than what Delco put in there originally.) As a result, operating voltages are all over the dartboard and some are outside the shop manual limits for the car. I'd get concerned about a constant voltage above 14.8vdc and any steady diet below 13.5 most likely won't keep the battery charged. I'm using an Autolite rebuild of the AC-Delco original right now (good gear because it's lasted over 3 years) and the voltage runs from 13.8 up to 14.4.
12.3 volts (engine not running) at the positive terminal is about right. 14.4 (running) at the alternator is OK too. It should vary from 13.5 up to 14.5 depending on load & rpm.
Enjoy the ride and don't sweat the voltages you're seeing. The usual disclaimer on your getting stranded applies -- don't call me! {{;-)
--
…PJ
’89 HookerCar, ’02 E-blu 6-spd Coupe
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Whoa..he said he measured 14.4 on the alternator. That's correct running, and his 12.3 engine off is ok too.
But Rich needs to remember that the 84 alternator is "different" from any other. And there was some interaction with the inside monitor, but don't remember what any longer, sold my 84 in 1997.
There is usually some resistor(s) used to scale the reading, which may be bad, but again, this brings back memories of chasing alternator problems in my 84 about ten years ago.
Another idea...there may be a voltage drop going into the car's systems, these are ties together down at the starter through fusable links. So, important test: car running...measure voltage at the cigarette lighter. If it is still up in the 14 volt range, or close to the battery voltage, the "car to charging" system is ok.
Remember too that in he C4 a common problem was a broken, loose, or otherwise bad ground connection at the instrument cluster, which can make readings bad.
Just some thoughts.
George C Red/Red LT-1

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