Charging system issue

[slayermanny]

Hi,

I seem to having an odd charging system issue that never happened to me with another car, so i wanted to see if anybody else might have had it happen to them.

About 2 weeks ago, my stock alternator stopped charging the car, it dropped for 14.4 volts to 12.7. The battery was at 83.5% charge. The alternator i bought was for GXP, so it didn't come with a decoupler.
It worked for about a week, then died on me during a 30 mins drive.

I checked the battery charge in engineering mode, and found that after a week it had only charged up to 85%. I figured the battery must have a dead cell, so i bought a new AGM-H7 duralast. After i changed the battery, the alternator started charging correctly again, and worked for the past 3 days without issue. Suddenly today, the alternator just stopped charging again, my volts hitting 12.8.

I wanted to know, is there a possibility that vibration might have loosened a ground somewhere and it isn't charging because of that? I have headers on, could the headers have cause heat damage to the alternator? They are coated, and it doesn't feel very hot under the hood after a long drive...

Did not buying the actual GT alternator instead of the GXP alt cause the problem? I'd like to have a good idea what to do, before i jump into buying yet another alternator.

[slayermanny]

So, here something interesting and annoying. Driving to lunch, the charging system reads 12.8 in engineering mode again, I stop at an advance auto parts, get the guy outside with his little machine. We go through the whole shake down, lights on, a/c on, 2500 revs and idle tests. Everything's fine. The car reads perfect on the Atari gauges and on his little computer. It had less than a minute to cool down, I was the only person at the store. What the hell man? I drive to lunch at home, boom. By the time get home the volts are back to 12.8. Turn it off, grab the keys, run inside, grab my multimeter that's right next to the door, turn her back on and check the volts: steady 14.7. I'm at a loss.

[slayermanny]

Ok. Drove her back to work, left the multimeter in the trunk to be able to check quick once the interior gauges showed under 14v. Pulled over and without shutting off the car i got 12.9v at the battery terminals, where i was getting 14.6-7v before. Guess the alternator took a dump. Alright, do i replace it with another GXP AC Delco unit, or do i go with whatever Advanced Auto or Autozone has?

[camopaint0707]

if they have one

[slayermanny]

Well, according to the websites, is have to ship one in regardless of where I got it from. However, the ac delco unit from a Chevy dealer online is much cheaper than the tough one unit from advanced auto. Anybody have any opinions on either?

[LDM]

Read the PDF file in this post by Crazy Paul: http://forum.grrrr8.net/showthread.php?t=39054 In particular, read the section about "Fuel Economy Mode." When the right conditions are met, the alternator output will drop down to battery open circuit voltage (12.5-13.1V). It keeps the battery charged, but is supposed to increase economy by lowering the output. This could be what's happening to you. It freaked me out the first time I noticed it in my car, thought the alternator was toast.

[slayermanny]

Wow. Ok, you just blew my damn mind.

...

So I'm gonna be running around for the next few days, making sure the battery stays above 80% charge. If it goes under, and the charging system doesn't kick back in, then I'll buy a new alternator.

Thanks man.

[Napalm]

the G8 like most newer cars has an adjustable field generator. the BCM of the car monitors conditions and varies the alternator output to match needs.

so yes it could be working just fine - but only output 12.7 volts. or it might not output any volts and the car run straight off battery for a while if it's got plenty of load demand.

likewise it protects the battery from overcharging and so on. when you test the alternator you need to do so with the AC on and the headlights on - heads and fogs if you just want to.

on your multimeter test DC voltage first - should be anywhere from 13-14.7 ish. then set your multi-meter for AC - check at the terminals again - should be between 0-0.6 voltsAC. why the rectifer circuit should correct all AC ripple - if you are getting more than 1volt AC - your rectifer circuit is beginning to fail and the car should sense it and complain - it is also gradually killing your battery if there is AC ripple.

the cheaper alternators you get from autozone and etc - also are varible output - why they are cheaper is because of cheaper bits in the rectifer circuit and cheaper or less dense windings - thus barely making current load.

[slayermanny]

The last 4 cars I've had all charge the battery from the moment it turns on till it turns off. This is why i love this forum.

[Rbarganier]

I bought the upgraded ppv 170a alternator last week it's awesome