Guys:

I started my car today and getting a :
1.) CHARGING SYSTEM FAULT
2.) SERVICE VEHICLE SOON

I'm getting 12.2 volts with the car off.
I'm getting 11.9v with the car running, and it dropped to 11.8v as I was idling.
I revved the motor and held it at 3000rpm for 10 sec and the voltage dropped to 11.75v.
Then back at idle it went back to 11.8v.

I have the charger on it now to pump up the battery.

I suspect the alternator is bad... what do you guys think ?

I believe that with the car running the battery should read 13+ volts right ?

I was thinking of pulling the Alternator tomorrow and have it tested.

Am I on the right path ?

Thanks !
Toque

 

Alternator or wires connecting it. Make sure the red wire is not loose or corroded on the terminal at the starter solenoid where the alternator and battery wires meet. You will interrupt the charge to the battery if it is. Alternator test is right path.

 

Thanks !

The terminal on the alternator is tight and no corrosion.

I was measuring my voltage on the tests in post #1 from the red wire on the alternator.

Toque

 

I was actually talking about the corrosion being on the starter solenoid bolt, but if you're measuring on the alternator and got 11v, the alternator is probably the problem.

 

Oh, sorry.. I misread your first post.
I'll check that connection tomorrow.

Thanks again !
Toque

 

If your alternator is bad, DO NOT turn it in as some kind of core until you find a correct replacement that actually works. Many people just have theirs rebuilt to avoid problems. Many supposed replacements do not have the correct electronic interface with the PCM.

 

^^^^ Good to know. Thanks for the tip !

Toque

 

If your alternator is bad, be careful with replacements. Check these postings from Evil-Twin on this matter. He gives a very detailed explanation on how this system works, and since the PCM controls and receives feedback from the alternator, anything that deviates from what it is expecting can set system faults.

1. Detailed explanation.

2. Replacing alternator with a higher capacity one.

3. Loads above the design point.

 

I first measured at the battery when the car was idling.
With my DVM.
I read 12.2v and it was dropping in volts as I was watching it.
I then went to the alternator red wire and frame gnd I watched it go from about 12v down to 11.8v.
Revving the motor made it go to 11.75v.
Back to idle it went back to 11.8v, but was still continuing to drop volts slowly.

I charged my battery last night and the charger reads full charge when I walked by it a monute ago. I don't think its the battery since it took the charge.

Thanks for the detailed info !

I'm pulling the alternator now to have it tested.




Yes I have heard of this issue. I am going to try to hold on to my original until the issue is resolved.

Thanks !
Toque

 

It can't hurt to have the battery load tested. It may show a "surface charge" of something like 12.6 to 12.8v, but a bad cell or an internal short can cause the battery voltage to drop quickly. A battery showing a very low 12v reading (12.0-12.1 or so) can indicate a bad battery.

 

Thanks for the tip !


Guys

Its not the alternator. It checked fine from O'reileys.

Battery with + removed is reading 12.79 with my DVM.
Its very stable. I watched it for a couple mins. No drop in volts.
I had charged it last night and removed the charger before I got the alternator checked 45 mins ago.

Think a battery check is still needed ?

Measuring resistance across the battery with my DVM I get an open circuit.

Strange little issue...

Just to give you guys an idea what I did recently.
I removed my engine covers, and installed some new valve covers, and coil relocation brackets.
I cleaned up the wiring and protected it with wire wrap.
I was very careful with the wiring.
I don't know if this could be related or not.
It started the first time I started the car after the install.

Thanks
Toque

 

Could it be that while doing all that the connector on top of the alternator that carries the control signals to and from the PCM got disturbed and it's making a bad contact?

 

There is a smaller red wire that comes from the solenoid and goes to the alternator at terminal D of the connector. This wire is used to power the regulator. It is also used to sense the "battery" voltage. In other words, it uses that voltage as the feedback to the regulator to control the output voltage. The alternator will not work if this wire is damaged and not connected. Check it.


These posts certainly have some wrong info in them. I'm not sure what makes the C5 alternator so tricky to replace but the reasons given in these posts are impossible.

The alternator can not start in generator mode and then switch to alternator mode. The alternator always works as an alternator, producing AC which is rectified to DC by the 6 internal diodes. To work as a generator the alternator must have a commutator, like in this picture.

http://store.eurtonelectric.com/imag...tail/63Bar.jpg


The alternator to PCM signal is a pulse width modulated signal. By definition, the duty cycle of a pulse width modulated signal can only go go from 0% to 100%. There is no way that duty cycle can go above 100% like written in the posts. If the alternator is rated for 110A then the duty cycle reaches 100% at 110A output. If the alternator is rated for 140A then the duty cycle reaches 100% at 140A output.

 

Guys:

So I put the alternator back on, re-connected the battery.

Volt meter idling car read 14.2 at the batt, 14.3 at the alternator.
Strange but true....
All I did was disconnect battery, and remove alternator for testing at Auto shop.
I wiggled some wires around and it was still good.

Went for a small cruise down my street and back home. No faults displayed on DIC.
Voltage good when I got home, and car displayed over 13v while driving.

Now I need to fix the fact that the spark plug on the drivers side next to the firewall is not in all the way.
It was HARD to get in there. I need to try harder to get it on I guess.

I could feel that I was not firing all cylinders.
Spray bottle with water stream on headers quickly told me which cylinder was not firing.

Thanks guys for your help !
Toque

 

I'm glad you are back in business and that neither your alternator nor your battery are bad

It might have been what I mentioned couple of posts above, that while working on your valve covers, brackets and wiring, the connector on top of the alternator got disturbed and developed a bad contact that was corrected when you removed and reinstalled the alternator. I can't think of anything else... But hey, congratulations!

 

Thanks !
I think your right. It must have been a connection since now everything seems ok now. Ill keep a close eye on it.

Thanks everyone for your suggestions !
Love this forum !

Toque

 

This guy is hard to listen to, but try and get thru it.

 

Thanks Ron ! Good information right there !
He should have also spoken about the starter and the connections there.

Toque

 

I broke down and purchased the double swivel socket from Snap On for the #7 plug.

http://store.snapon.com/Double-Swive...t-P642284.aspx

Made that plug tolerable, plus having my 2 C5's and my son's Z06 it was a good investment.

 

Very nice ! Thanks !

Someone recently told me about a cut down socket that a corvette vendor sells for $25 that works great on #7 plug.
I just need to remember what vendor it was....

Toque