Charging problem
Thread Starter
8th Gear
Joined: Aug 2007
Posts: 8
Likes: 0
From: Naperville Illinois
Charging problem
Hi all,
I am a new member and wanted to say hi and get some advice. When I am driving my 85 and come to a stop light the voltage drops quite a bit, sometimes as low as 11.5 depending on what accesories I have on. I own an auto shop and my techs have put in a new alternator, rebuilt the voltage regulator on that alternator and ran new wires to and from the alternator. I even went so far as to put an optima battery in the car to see if that would help. If I am driving it will charge the car at between 13.3 and 13.8 but never above that and if I have the ac on it really drops. It never dies on me but I would really appreciate any advice you can give me. I am also always here for any advice you may need since all of my techs have at least 6 ASE certifications each so even though I may not know the answer I can get it from them, alldata or identifix. Looking forward to being a member of this community and meeting any Chicago area c4 enthusiasts such as myself.
Thanks for the help.
Bill
I am a new member and wanted to say hi and get some advice. When I am driving my 85 and come to a stop light the voltage drops quite a bit, sometimes as low as 11.5 depending on what accesories I have on. I own an auto shop and my techs have put in a new alternator, rebuilt the voltage regulator on that alternator and ran new wires to and from the alternator. I even went so far as to put an optima battery in the car to see if that would help. If I am driving it will charge the car at between 13.3 and 13.8 but never above that and if I have the ac on it really drops. It never dies on me but I would really appreciate any advice you can give me. I am also always here for any advice you may need since all of my techs have at least 6 ASE certifications each so even though I may not know the answer I can get it from them, alldata or identifix. Looking forward to being a member of this community and meeting any Chicago area c4 enthusiasts such as myself.
Thanks for the help.
Bill
Drifting
Joined: Sep 2003
Posts: 1,363
Likes: 7
From: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
-- both alternator/battery and dash board grounds.Also, presume your year has a digital dash and your quoting it. Has the digital dash gauge been compared to another gauge when driving to assure it is correct?
Has the alternator been bench tested to confirm it meets specs, as I have heard of 'new' not meeting specs, which could account for it not being able to maintain voltage with load at lower RPM.
Any chance that the pulley is the incorrect diameter and the alternator is not achieving its minimum RPMs?
It would appear that the 1985s started off with a 108 amp alternator (production # 01105450 -> 01105584), and then was upgraded to a 120 amp alternator (01105585+ & 10464392+).
In either case, the 'service' (replacement) alternator should be the 120 amp alternator, GM part # 10464392.
Was the 120 amp rated 'new' alternator installed?
Thread Starter
8th Gear
Joined: Aug 2007
Posts: 8
Likes: 0
From: Naperville Illinois
We changed the pulley to a smaller pulley when we noticed a 2000 Yukon had a smaller pulley on it then my vette did. I also drove it with an Edtronics 1080 battery/alt and starter hooked up and the loads were off .4 but it was still low when at an idle and never above 13.8 at any speed. I dont really rely on the alt gauge anymore for specifics just for estimate. The alt I put in was 120 v and not even a remanned on, it was totally new.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
The dash voltmeter reads 0.3 v low because it measures voltage after the ignition switch contacts which have 0.3 v drop. Also, alternators cannot generate their rated current at idle rpm and if you have a large electrical load, the alternator output voltage sags and the battery picks up most of the load current. When you get underway the alternator should provide your car's electrical requirements and the dash voltmeter should rise to 13.3 v hot. Also, it is by design that the alternator puts out 14.7 volts cold and the voltage drops to 13.7 v (at the battery terminals) when it gets to its operating temperature. My 87 maintains 13.3 v (dash voltmeter) hot, even idling. Maybe someday when I can ever get the !@#$%^&* a/c working, I'll see below 13.3 v idling.
