Alternator issues???
Thread Starter
Advanced
Joined: May 2008
Posts: 70
Likes: 1
From: Pensacola FL
Alternator issues???
Hello,
1978 Vette, no mods, simple radio, When I start the car the voltage reads right above 13.. after driving for 20 minutes or so voltage starts to spike to the red and back when moving, like a bouncing motion, at a light or at idle it will go back to right above 13.. had alternator tested and "they say" it was fine..also the light does not come on for the GEN I know it works. can anyone help and lead me in the right direction please..
1978 Vette, no mods, simple radio, When I start the car the voltage reads right above 13.. after driving for 20 minutes or so voltage starts to spike to the red and back when moving, like a bouncing motion, at a light or at idle it will go back to right above 13.. had alternator tested and "they say" it was fine..also the light does not come on for the GEN I know it works. can anyone help and lead me in the right direction please..
Instructor
Joined: Jun 2006
Posts: 146
Likes: 5
From: North Brunswick New Jersey
Can't diagnose from here but, I can relate that I had the same problem after exchanging my alternator from a rebuilder. He also said my alternator was 'fine' when tested. I was not satisfied with the voltage spikes so I went to NAPA and bought everything needed to rebuild the alternator myself. Fairly simple change-out of parts and now it no longer spikes into the red; just a couple volts above twelve after starting and the settles down to about thirteen, like it used to.
Safety Car
Joined: Nov 2004
Posts: 4,359
Likes: 57
From: Mundelein Illinois
Either alt or guage is bad. Alt way work fine until it heats up, that is why the parts store says it's fine. As you stated, light does not come on so alt is not overcharging or undercharging, this would make me think guage.
I would change alt, if problem still exists, I'd replace guage.
Just my 2 cents worth
I would change alt, if problem still exists, I'd replace guage.
Just my 2 cents worth
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
any time you have a reading above 12 volts ie {for the battery} the only way that can happen is by the alternator and proof that it is charging. But it should not go below. The regulator is built into the alternator so it would have to be exchanged or taken apart to repair if the alt is at fault....try a remote volt meter and check the reading. They say 13.6-14.4 is optimum. and possibly check the plug in the side of the alt for corrosion
Thread Starter
Advanced
Joined: May 2008
Posts: 70
Likes: 1
From: Pensacola FL
Also the headlights will get brighter when the spike occurs, would that alternator do this if heated up?? and would that mean its bad even though the auto store said it was good?? thanks again
Drifting
Joined: Apr 2007
Posts: 1,970
Likes: 45
From: Cameron Park CA
It sure could be the voltage regulator. I had a similar problem awhile back with the ammeter. It would jump around from a normal reading just into the charge side, to jumping way over to the right - heavy charging. I replaced the solid state regulator (it's pretty cheap) and problem solved.
Cheers,
Pete
Cheers,
Pete
Le Mans Master
Joined: Aug 2006
Posts: 7,426
Likes: 1,559
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Here's a HOW TO: you can take the alternator apart and test the components. It won't cost any thing except if you find a bad part then you can get whatever you need at NAPA.
http://www.4wheelnoffroad.com/alter.html
I'm pretty sure that the test at the auto parts just indicates output but does not identify a bad diode trio.
http://www.4wheelnoffroad.com/alter.html
I'm pretty sure that the test at the auto parts just indicates output but does not identify a bad diode trio.
Last edited by Peterbuilt; Apr 30, 2010 at 01:18 AM.
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Drifting
Joined: Apr 2008
Posts: 1,305
Likes: 2
From: Lewisburg WV
thegazman
It sure could be the voltage regulator. I had a similar problem awhile back with the ammeter. It would jump around from a normal reading just into the charge side, to jumping way over to the right - heavy charging. I replaced the solid state regulator (it's pretty cheap) and problem solved.
Cheers,
Pete
Cheers,
Pete
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
I highly suspect that your ground strap [between engine and frame] is defective or making poor connection. A buddy just had the very same symptoms with his '67 Nova (modified car with an alternator having the integral regulator); I thought it was probably due to an alternator component in the regulator, but steered him to a good alternator/starter repair shop. The owner took one look at it and said he could easily change out the regulator components but that he would be wasting his money, and that the problem was a bad ground.
Sure enough, he checked it and the ground connection was bad. Once that was fixed, no problem since. Good luck.
Sure enough, he checked it and the ground connection was bad. Once that was fixed, no problem since. Good luck.
Le Mans Master
Joined: Aug 2006
Posts: 7,426
Likes: 1,559
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Thanks for posting back with an answer. 9 years ago I got a rebuilt from Auto-Zone, 5 years after that a bearing failed. Free replacement and no hassle and an alternator is an easy part to remove and replace.
Burning Brakes
Joined: Dec 2008
Posts: 971
Likes: 45
From: Middlesex NJ
I highly suspect that your ground strap [between engine and frame] is defective or making poor connection. A buddy just had the very same symptoms with his '67 Nova (modified car with an alternator having the integral regulator); I thought it was probably due to an alternator component in the regulator, but steered him to a good alternator/starter repair shop. The owner took one look at it and said he could easily change out the regulator components but that he would be wasting his money, and that the problem was a bad ground.
Sure enough, he checked it and the ground connection was bad. Once that was fixed, no problem since. Good luck.
Sure enough, he checked it and the ground connection was bad. Once that was fixed, no problem since. Good luck.
You may very well have had a bad alternator but you had to disturb the ground while replacing it. These old cars have had their grounds out in the open for far too long and they should be gone over and cleaned up reconnected then covered with a dielectric compound to prevent oxidization. Never know when bubba left it off being lazy and relied on the brackets and block to ground it.