About a month ago I had started to notice a minor drop in my voltage on my 1996 'vette. About a week and a half ago the volts dipped below13v, so I went and had the battery and alt tested, Battery showed only holding a charge of 77% and alt was reading 0 amps at idle. I replaced the alt and battery on saturday with a 'Premium Palladium' advance autor parts Part Number: P817313, Battery was the walmart maxx 75n battery. Imidiantly after instally volts was back to a normal 14.7v but after driving it to work that day, it was reading 13.3v. Sunday it had started to dip to 12.9v at idle if id press the break, with nothing on. And then today 12.7v with the ac on. When driving and giving the car gas, maintaining a rev of around 1300+ rpms the charge would read 13.8-14.0 volts.

I figured I had just gotten another bad alt. So took the car to advance and had them test it, but the guy there said it was good, although when I was watching the guages when he put a load on it I saw it dip to 11.5v with a load then jump to 13.8v (not even hitting 14v now) as the engine reved. When stopping at a light I have to maintain a little rev to 1300+ now to keep the voltage to 13+v with ac running, if I didnt do this you would notice a drop in the fan speed too and would notice the increase if I reved it. Also tonight on the way home from advance with the lights on, when stopped I was sitting at 12.5v

He said its normal for when the alts to kick on for them to drop down to that voltage. Myself I had done some searching here this morning and found several posts stating that voltage shouldnt ever get below 13.

If the alternator is good as I was told, what else could be the problem? or is it normal on '96's to run that low on volts?

Btw I have a 1996 Lt1 coupe.

 

Usually my experience with these kinds of problems turns out to be the main grounds, and the main 12V supply from the battery and the alternator to the starter post. They live in a harsh environment and corrode over time. A new battery will mask the problem for bit because the extra current can sometimes override the corroded connections. But with time they will only corrode further as more and more carbon builds up on those connections.

When we installed a new motor (friends 95 LT-1) just two weeks ago I was surprised the thing started or didn't have electrical problems. The battery ground cable looked all grey and dirty where it attached to the transmission. The positive cable at the starter looked even worse.

I have a 96 also and notice at night with the lights on they dip in dimness at times, usually during hard acceleration. I'm almost positive I'm going to find the same corroded connections at the starter and the main grounds.

 

Thanks for the reply, allt4, ill get out there tomorrow since its my day off and check out those connections. Thanks

 

Engine cold and running, the dash voltmeter will read 14.3 volts due to 0.3 volts drop across the ign sw contact resistance (battery voltage will be 14.7 v) and as the engine gets to operating temp the alternator output drops and the dash voltmeter will read 13.3 volts (this is normal). Unless you have different pulleys to reduce accessory parasitic load or you have an unusual electrical load, at idle the dash voltmeter should hold up in the range 14.3 v cold to 13.3 v hot. Measure the battery terminal voltage (engine hot) while someone hits the brake to confirm that the battery terminal voltage follows the dash voltmeter. Also check the voltage at the alternator output terminal, it should be identical to the battery terminals voltage. The dash voltmeter might drop with the brake because of voltage drop across the ign sw contacts from the added brake lamp current (defective ign sw). If you have normal idle speed, turning on the a/c should not drop the dash voltmeter (you will see a momentary drop as the voltage regulator in the alternator cannot instantly correct for a sudden increase in alternator load current).
A fully charged lead acid battery has a voltage of 13.2 volts, so if you ever see a voltage below 13 volts, your battery is supplying current to your car electrical load and if the engine is running , this should never happen.

 

Looks like I may have misled you, I checked my manual and the battery goes to a fuse block on the fender well. Also another seperate run goes to the starter.

Here's a photo album with some pictures that may help...

http://www.personal.psu.edu/gls17/charging/index.html

 

thanks a bunch, yeah ill be pulling out the meter tomorrow and testing all of this.

 

Well don't be a stranger if you find out what's wrong. One thing we all hate is when we never hear the out comes or solutions to folks problems.

It makes us all feel good to know when something we've posted has helped someone.

 

actualy things came up and havent had time to get to the car something I did notice today before I worked that when I put the car in reverse is when it shows its lowest voltage, with the ac on it was at 12.5. work tomorrow at 1 but hopefully I can get in there and mess with some of hte grounds. Need to go by and autostore and pick up a manual though first so I can find these easier heh.

I will keep this updated though.

 

If you are going to spend money for a manual, get the best one out there which is the one GM sells. All the others are not anywhere as complete as the GM. Also, for electrical problems, the GM electrical diagnosis service manual supplement is extemely good. It has the circuit diagram, an explanation of how each circuit works, a diagnosis chart for typical problems and a list and pictures of where the system components are located including wire colors and ground lug locations.

 

All valid information so far but just let me add some information on the WalMart battery. I needed a battery for a vehicle that does not leave my property. Got a WalMart battery and have returned it twice so far under warranty. Never had this kind of problem with a new battery ever. I’m not saying they sell junk, just stating some facts. But I will never put one in any of my other vehicles.

My numbers run generaly from 13.9 to 14.5 and normally hovers in the middle.

The GM manual is well worth it and specific to your car and systems. The other books are Ok to own for some quick reference and pictures in addition to the GM book. But for a primary book, 10 electrical diagrams that are generic don't cut it for these cars with the amount of electrical there is.

 

I see nothing unusual about those numbers...at all.
Perfectly normal, I'd say....

Larry
code5coupe