C-4 Voltage Problem
Thread Starter
Cruising
Joined: Oct 2010
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C-4 Voltage Problem
Hi Guys looking for a few suggestions. I have 85 corvette with digital dash. Just the other day I got an alarm with a red bar saving voltage problem. It is putting out between 17.8 to 18.2 on the digital display. I know the battery is good and I just replaced the (alt) today, with no change. I still get the alarm with 18.2 volts. Any suggestions. Tks Wayne
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
That voltage is way too high. I know on my car (different ECM) that the ECM won't let you start the car if the voltage is too high.
It's possible the voltmeter is just reading incorrectly. The way to find out is to measure the voltage at the alternator while the engine is running. When the engine is not running you will be measuring the battery voltage.
It's possible the voltmeter is just reading incorrectly. The way to find out is to measure the voltage at the alternator while the engine is running. When the engine is not running you will be measuring the battery voltage.
Le Mans Master
Joined: Oct 2004
Posts: 6,314
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From: South-central Missouri
with Cliff. If you changed the alternator, and still are getting the (dash) high voltage problem, I'd want to put a volt meter on it to see what is really going on, as "step -1".
Team Owner
Joined: Dec 1999
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
Just as suggested in your same thread in the C4 Tech section. 
But do the check not only at the alternator, but at the battery (both with engine running and off). I would make sure the battery has a full charge before testing voltage. Battery voltage with a full charge (engine off) should be around 12.7 to 12.8 volts.
A good alternator should provide around 14.1 to 14.3 volts after engine start, then slowly drop to around 13.6 to 13.8 volts depending on what accessories are turned on.
Where did the alternator come from? One of the chain parts stores? Sometimes the part store rebuilds are poor quality. You may have gotten one that is bad. I would take it back and get another one. If funds allow, consider buying a brand new alternator. AC Delco or Bosch are good choices.
Thread Starter
Cruising
Joined: Oct 2010
Posts: 10
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Just as suggested in your same thread in the C4 Tech section. But do the check not only at the alternator, but at the battery (both with engine running and off). I would make sure the battery has a full charge before testing voltage. Battery voltage with a full charge (engine off) should be around 12.7 to 12.8 volts.
A good alternator should provide around 14.1 to 14.3 volts after engine start, then slowly drop to around 13.6 to 13.8 volts depending on what accessories are turned on.
Where did the alternator come from? One of the chain parts stores? Sometimes the part store rebuilds are poor quality. You may have gotten one that is bad. I would take it back and get another one. If funds allow, consider buying a brand new alternator. AC Delco or Bosch are good choices.
Last edited by whmartin98; May 27, 2013 at 07:59 PM.
Thread Starter
Cruising
Joined: Oct 2010
Posts: 10
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Thanks for the information, I thought somehow changing the ECM may correct my High voltage problem. Sorry to hear it is in the cluster, If this is my only trouble in the cluster which it is, I guess I will live with it until another issue in the cluster comes up. Again Thanks for your thought, Wayne Tn.
Race Director
Joined: Apr 2002
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From: Anaheim CA
Well, you could always look at coolant temperature instead...
I just remembered that the cluster will switch to the display that is showing the problem automatically. You might not be able to switch to coolant temperature. I know mine switches to the voltmeter if the voltage is below 11.5 volts. I don't know if it does that if the voltage is too high.
I just remembered that the cluster will switch to the display that is showing the problem automatically. You might not be able to switch to coolant temperature. I know mine switches to the voltmeter if the voltage is below 11.5 volts. I don't know if it does that if the voltage is too high.
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Thread Starter
Cruising
Joined: Oct 2010
Posts: 10
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Well, you could always look at coolant temperature instead...
I just remembered that the cluster will switch to the display that is showing the problem automatically. You might not be able to switch to coolant temperature. I know mine switches to the voltmeter if the voltage is below 11.5 volts. I don't know if it does that if the voltage is too high.
I just remembered that the cluster will switch to the display that is showing the problem automatically. You might not be able to switch to coolant temperature. I know mine switches to the voltmeter if the voltage is below 11.5 volts. I don't know if it does that if the voltage is too high.
Burning Brakes
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