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1986 Corvette not charging

kjordan

Member
Joined
Mar 26, 2003
Messages
5
Location
Macon
Corvette
1986 Bright Red Coupe
I have replaced three batteries and the alternator once, but my 1986 corvette continue to lose charge as you are driving or let it run in park. Eventually it cuts off. The amp meter in the corvette reads 12 when the battery is fully charged but it drops as soon as the vette begin to run. What am I missing?
 

bradfordsvettes

Well-known member
Joined
Mar 28, 2001
Messages
549
Location
Boston, MA area
Corvette
jewel blue 61.cranberry 69 t-top.black rose 92
may still be a bad alternator a rebuild or new only means just that not that it is working . I have installed many new or rebuilt parts that were junk . but do not rule out a wiring issue just my 2 cents Steve
 
A

auto_x_al

Guest
from what I have seen you have to make sure that the battery is fully charged before you fire the car with the new alternator. If you have a battery that is half dead the new alternator will burn up trying to charge the battery and keep the car running as well. This seems to be a problem unique to C4's.
 

pns0ccc

Active member
Joined
Dec 9, 2002
Messages
41
Location
Bradenton, Fla.
Corvette
1996 Triple Black
The voltage you're looking for is 12 to 12.2 without the car running. Once started the alternator or charger should increase the voltage to 14 volts approx. Voltage regulator, alternator, battery or connection. If you remove alternator from the car you can have it tested at one on the auto parts stores.
If the Alternator tests within specification test the battery with a smart trickle charger and it will either take a charge or indicate fault. Or take the battery to sears who can test if the battery will accept a charge.
 

86PACER

Well-known member
Joined
Dec 31, 2002
Messages
182
Location
CA
Corvette
1986 Pace Car
I agree with what has been said.

The new alternator could be bad too. What's your idle RPM's? Return it, and this time have them bench test the replacement in the store before you take it home.

The most common cause for an alternator to stop charging is a worn brush assembly that cost less than $10. For that you need to crack open the alternator, which is not that hard to do.
 

Andries

Member
Joined
Nov 29, 2005
Messages
18
Location
Cambridge, UK
Corvette
1994 Dark red coupe
It is worth checking all connections, also the earth from battery to chassis. put a voltmeter directly on alternator and the check voltage with car running, should be 14 but if the dash say 12 i'm pretty sure the alternator is not charging.
Earth/ground on mounting bracket. Positive current to battery big red wire (should be 14v with car running) Two small wires, one 12v live with car on and not running, both live with car running. If car started fine and only live on one wire it also means not charging.
I've actualy got a problem on my other car (french s*&t renault) where I got to hit the alternator with a hammer once a month to get it start charging. Regulator I guess)
 

Jeb

Well-known member
Joined
Jan 20, 2005
Messages
456
Location
Covington, Louisiana
Corvette
1987 Convertable
It is worth checking all connections, also the earth from battery to chassis. put a voltmeter directly on alternator and the check voltage with car running, should be 14 but if the dash say 12 i'm pretty sure the alternator is not charging.
Earth/ground on mounting bracket. Positive current to battery big red wire (should be 14v with car running) Two small wires, one 12v live with car on and not running, both live with car running. If car started fine and only live on one wire it also means not charging.
I've actualy got a problem on my other car (french s*&t renault) where I got to hit the alternator with a hammer once a month to get it start charging. Regulator I guess)

That's strange.

Normally with something French, all you have to do is threaten to hit it with something and it'll start running. That must be a stubborn alternator.

Ok, Ok, Ok. It was just a joke.:eyerole
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
MY 2 cents

OK just to reinforce what the others have said. I had a bad alternator on a car I had and so I went to the Parts store and picked up a rebuild. I rushed home and installed it and you know the answer it did not work. Back to the store for another. I did this 4 times that day until the store ran out of alternators for a Chevrolet and I started on the ones for a Pontiac before I got one that would charge. I have been using a homemade meter to check the charging system since. ( There is always a question if the meter is right.) I went to Radio Shack and bought a cigarette lighter plug in adapter with wires on it so I could hook up my volt meter in the car and check the charging system independently.(This adapter has a switch and a fuse with it).
As said before no load voltage should be about 12.2. The starting voltage should not drop below about 10 volts when the starter is engaged and turning the engine over. The voltage while the car is running should be 13.7 to 14.2 give or take. If the voltage falls in this area all is well but if lets say the voltage on the start up is less than 10 volts then your battery may be suspect only if all the other voltages are in line. Another thing you can check with this set up is whether there is a drain on the battery other than your meter with the car not running. I have used this meter checking method to find out that the alternator on my Olds was spiking causing my lights to go dim and bright. That alternator would spike as high as 18 volts at times yet every check the battery stores made said it was good at idle.
good luck with your problem.:confused
 

kjordan

Member
Joined
Mar 26, 2003
Messages
5
Location
Macon
Corvette
1986 Bright Red Coupe
Charging Issue Solved, thanks

I had a chance to remove and check the alternator. You all were correct. The alternator was not charging. I found a new alternator had it checked it was good. Everything working as designed.
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
Thanks

Thank you for the end of the story. When the solution is posted we all gain knowledge about our cars.:upthumbs
 

Edmond

Well-known member
Joined
Aug 1, 2001
Messages
5,218
Location
Louisiana
Corvette
2003 Z06
I had a chance to remove and check the alternator. You all were correct. The alternator was not charging. I found a new alternator had it checked it was good. Everything working as designed.

Good news. I was late getting in on this thread but I generally highly recommend against buying used or rebuilt or non-OEM electrical parts. To me, OEM parts offer the least variance and that is especially important in electrical parts.
 

jester

Well-known member
Joined
Nov 16, 2001
Messages
173
Location
Savage, MN, USA
Corvette
1988 35th Anniversary Edition
Good news. I was late getting in on this thread but I generally highly recommend against buying used or rebuilt or non-OEM electrical parts. To me, OEM parts offer the least variance and that is especially important in electrical parts.

When I replaced my second alternator in a year, the guy in the parts store adivsed me to spend the extra money for the AC rebuild and not go with the store brand rebuild. I did that and haven't had a problem in the six or seven years it's been in.
 

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