Hello...I'm new to this community and I have a question...

I have a 2003 Convertible. I started having problems with the volts jumping up and down as I was driving a few months back. I'm in Las Vegas so I'm used to the car being a little finicky in the summer because of the heat.

My husband took the red top Optima battery out, had it tested, they said it was ok. It's not even 3 years old but out here in the heat, batteries don't last as long. Since it tested ok, he took the alternator out and had that tested, also told it was ok. So, the parts store said they would replace my battery. Now, new battery, same problem. Volts start out at 13.9-14.1 but as it's driven they fluctuate to as low as 11.7, the car has even stalled.

Next, my hubby changes the alternator just in case. Problem still occurs, we take it back, have it tested and it took until the 3rd test to show it was bad. Another new alternator has been put in, still having the same problem. I should mention that we replaced the alternator with remanufactured product because OEM is so expensive.

Also...there have been NO dash lights or codes showing that there is a problem. I know I should take it and have the charging system checked but I thought I would ask if anyone else has any suggestions as to what the problem may be.

Another thing, The pulley that is at the bottom of the engine seems wobbly. Could this have something to do with it?

I've had people suggest that it may be the starter but they also were not drawing on Corvette experience.

Any help is greatly appreciated. Thank you, sorry for the long post!

 

Welcome to the forum.

Most auto parts stores will check the battery and alternator in the car for free. That way you don't have to throw parts at the problem. They will also scan for codes.

Make sure the alternator belt is tite. I assume it is a serpentine belt, so the tensioning idler should be checked to make sure it's free. While probably not part of the problem, I'd get the "wobbly" pulley checked. Not sure how the starter could contribute to the problem.

On the 2007 and up Tahoes, the ECM controls the alternator output and it's not unusual for it to drop to 11.XX volts. Not sure if Corvettes do that.

 

I seriously doubt that the starter is causing the problem. The only time it comes into play is while starting the engine. After that it's just along for the ride. I suspect a defective cable, loose connection, or the most overlooked item, a bad ground. Do a good visual inspection of all ground connections and cables. Also check the positive cable connections between the alternator and battery. The older Chevrolet products used the positive cable connection on the starter as a junction point for the charging system as well as the main power feed for the rest of the car. I'm not sure if the C-5 still did this, but it is worth a look.

If the visual inspection does not locate the problem, you should do a volt drop test of the battery cables including the ground cable. To perform this test you take a DVOM (digital volt ohm meter), set it to read volts, connect the red test lead to one end of the suspect cable, and the black test lead to the other end of the same cable. (does not matter which lead to which end. the volts just might read as -volts.) It will read 0.0 volts at this point. Now have an assistant crank the engine to start, while you read the meter. A good cable will read .5 volts or less. Anything more than that is considered excessive. I have found cables that looked perfectly fine, but would loose several volts while under load. For the alternator output cable do the same test, just check the voltage between the alternator output terminal and the battery positive post while the alternator is charging. Then check between the alternator ground and the battery negative post with the alternator charging. You should have the headlights on, high beams on, and a/c blower fan on high to put a load on the alternator for an accurate test. If either circuit fails the volt drop test, work your way back through the circuit connection points to isolate the problem's exact location.

I have one question for you. When the volts dropped to 11.7, was that measured at the battery, or from the instrument display? If it was from the instrument display, did anyone verify that the battery had the same voltage? If it displayed 11.7, but the battery was still at 12.4 for example, this would indicate that the voltage feed to the instrument panel and probably the rest of the interior was at fault. Time to dig out the wiring diagrams, and search for the voltage feed.

I have some other ideas if you still need help, but this post is getting a little long.

Good luck, Gumby

 

Thanks for the ideas...I'll have my hubby check them out. All the readings of the volts when they fluctuate have been on the instrument panel. You can feel the car shudder when they drop real low.

We actually drove it for a while today and according to the instrument panel, the volts are staying between 13.5 to 14.3 for most of the time. It dropped to 12.7 once when I was coming to a stop.

Thank you for the help, Shannon

 

Did you ever figure out your problem? I'm having the same thing happen to me.

 

My husband took the 2nd alternator in to have it tested and before they tested it they told him that they now carry the 140amp alternator so he got that instead and we haven't had a problem since.