Fluctuating voltage???
Thread Starter
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Fluctuating voltage???
When cruising along an Interstate at 65mph in 6th gear I noticed the analog voltmeter was fluctuating somewhat wildly, kind of what you might expect on a real bumpy road..this was daylight with no lights on, as an experiment I did put the headlights on with no apparent resulting change
Checked the digital gauge and as it refreshed itself about every second a new random reading came up....the readings were all between about 13.4 and 15.0 volts..
Everything else seemed normal..
We are talking about my 1996 LT4...
Suggestions??
Checked the digital gauge and as it refreshed itself about every second a new random reading came up....the readings were all between about 13.4 and 15.0 volts..
Everything else seemed normal..
We are talking about my 1996 LT4...
Suggestions??
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
Probably the voltage regulator.However I had a weird experience with my 280ZX where the voltmeter went wild. The problem turned out the be a shorted battery. There was no indication of a problem till it just happened. Glad I was in a Sears parking lot and got a battery right there.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
You should check voltage using a digital volt meter to remove any chances of the wiring or the gauge itself being bad. Set the DVM to a setting for reading up to 15v and use the + probe to check voltage at the terminal at the alternator post. Run the engine through different RPM levels and see what the readings are and if there is fluctuation.
Also check battery voltage with the engine off and then when running. A fully charged battery should read around 12.8v with the engine off (remember to close the car doors, ignition off and wait until the interior lights go out). Then check the battery again with the engine running. You should see very close to the same voltage readings as you got at the alternator, something like 13.2v to 14.3v or so.
Fluctuating readings like you describe is usually the internal regulator inside the alternator.
Also check battery voltage with the engine off and then when running. A fully charged battery should read around 12.8v with the engine off (remember to close the car doors, ignition off and wait until the interior lights go out). Then check the battery again with the engine running. You should see very close to the same voltage readings as you got at the alternator, something like 13.2v to 14.3v or so.
Fluctuating readings like you describe is usually the internal regulator inside the alternator.
Thread Starter
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Since it's going as high as 15 volts I agree with everyone who said defective alternator, or to be more specific, the internal regulator. If it's a high mileage unit I would just get a new alternator.
c4cruiser gave the best advice, verify readings with a digital voltmeter, if that shows normal then it's not the alt.
c4cruiser gave the best advice, verify readings with a digital voltmeter, if that shows normal then it's not the alt.
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Thread Starter
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Well it turns out the problem was a bad negative terminal battery connection that was corrected by simply tightening the connection.....
Fortunately it turned out to be a simple fix....not really what I was expecting...thanks for everyone's input
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
That’s a unique fix for that problem. Bet nobody would have guessed that and if they did all would probably think they were bats.
But it does occur to me that you might have had a cranking or starting problem also. Stranger things have happened I guess.
Last edited by pcolt94; Nov 25, 2009 at 10:45 AM.
Thread Starter
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
actually I drove it to the car wash and when I tried to start it, I heard an electrical pop and EVERYTHING went out...no cranking or anything
started looking around and found I could rotate the negative cable on the battery post.....snugged it up---car started, idled normal and no more fluctuating voltages..
