2008 silverado charging behavior

[eljefino]

Got this truck in June. Was a bit of a mess with the door latch wiring cut in the hinge, so it would leave the radio on for a while after shutdown. Suspicious of parasitic draws, I removed both onstar fuses. Is W/T trim, no glove box light or fancy junk. Has a new, as of June, oversized group 65 WM Valu-Start battery. Yanked it this week and it tested good.

Truck gets driven once a week, to the dump. Runs for 20 minutes, once a week. I've put trickle chargers on it now and again due to under-use and a presumed bunch of convenience modules sapping power. 240k, 4.8, 4L60E, 2wd. Truck has computer-controlled charging. Installed a digital voltmeter that runs off a switched ignition feed. Have watched this voltmeter since summer.

It typically likes to run at 14.9-15.1 volts. Doesn't matter the outside temp, if the headlights are on, or if it's in tow-haul mode, both things that are supposed to boost system voltage. But, this first time after replacing the battery, it ran a solid 14.0. Cold, hot, any RPM. I park it, restart it, and it's back to 14.9. What gives? What other inputs does this truck use to set its system voltage?

I am not a heavy power user, in fact I disabled my DRLs. Only codes are a small EVAP leak.

 

[tyman]

GMs regulated charging system.

Gears Magazine - High Output: A Look at Today's Charging Systems

The longer I’m around, the more I realize the importance of the basics. How many times have you tackled a complex vehicle issue, only to find the problem was something really basic? With each year’s seminars, I find that we likely have some information that deals with system powers and grounds...

gearsmagazine.com

 

[LeakySeals]

GMs regulated charging system.

Gears Magazine - High Output: A Look at Today's Charging Systems

The longer I’m around, the more I realize the importance of the basics. How many times have you tackled a complex vehicle issue, only to find the problem was something really basic? With each year’s seminars, I find that we likely have some information that deals with system powers and grounds...

gearsmagazine.com

Interesting. What's more interesting is how you were able to highlight and create a link to that section of the article.

 

[eljefino]

^ By that article's logic I'm getting a desulfate mode, perhaps because the truck knows it's been parked a long time. Except for the time I just connected the battery, then it went with a default.

 

[eljefino]

Update.

Changed the starter because I felt like maybe the old one was "dragging", taking too much current to provide not enough motion. I was right. New starter works great.

Have noticed that the truck seems to monitor something while the starter is operating, and bases its voltage profile on info from that. IDK if it's a lowest voltage point or if it has some ammeter looped around the main battery cable, but somehow, it knows.

A cold start, dipping to the high 9 volt range, gives me 14.9-15.3 volts for the 20 minute trip to the dump and home.

A warm restart gives me less... 14.3 to 14.5 at the same ambient outside air temp. I needed the new starter to see this "warm restart" mode because the old starter would always drag and put the truck in "panic charge" mode.