Interesting charging behaviour

[OVERKILL]

So, now that the Jeep seems to be fixed (it also has a new alternator it didn't need) I've been watching the voltage to confirm. Problem was a loose main body ground near the battery.

Some quick data: Vehicle has a 220A alternator which appears to be made by Denso. Battery is a factory AGM situated beneath the passenger seat.

Upon initial, and most starts, charge voltage sits around 14.6V, usually going no lower than 14.5V and no higher than 14.7V.

HOWEVER

Some starts it will sit around 13.5V and go no lower than ~13.4V, no higher than 13.6V.

Next start, it will be back at 14.6V.

I've noticed this primarily occurs on a hot start after you've driven it for quite a bit. However, I've not noticed it step down to this voltage range while in use. It seems to take a stop/start cycle for this to occur.

I'm guessing it may have something to do with battery health charge programming but that's based on nothing. Dealer has no idea, thinks it might be what I'm thinking. No idea if it has always done this, as I was not constantly monitoring the charge system prior to these recent issues.

Thoughts?

 

[Rand]

Does that have ESS being the SRT model?

Not familiar with options on the ?6.4L?

 

[OVERKILL]

Negative, just MDS.

 

[clinebarger]

If it only happens on a hot start, The ECM knows the alternator doesn't need to "top-off" the battery. Just a guess though!

From a diagnostic/customer complaint standpoint....I would make sure that the Regulator Commanded On-Time (Duty Cycle) matched the Voltage Output at the charge post.

I wonder if the dealer flashed in the latest calibration & Alternator behavior IS now different? In my time working as a dealer tech......New calibrations changed all kinds of things & the manufacturer doesn't let you know WHAT got changed.

 

[OVERKILL]

Originally Posted by clinebarger
If it only happens on a hot start, The ECM knows the alternator doesn't need to "top-off" the battery. Just a guess though!


That was my thought too, as noted

Originally Posted by clinebarger
From a diagnostic/customer complaint standpoint....I would make sure that the Regulator Commanded On-Time (Duty Cycle) matched the Voltage Output at the charge post.


It does.

Originally Posted by clinebarger
I wonder if the dealer flashed in the latest calibration & Alternator behavior IS now different? In my time working as a dealer tech......New calibrations changed all kinds of things & the manufacturer doesn't let you know WHAT got changed.


Negative, it had the latest calibration before it went in (I checked it the week prior when I first pulled the codes on it, all the modules were up-to-date). There was nothing in the errata that mentioned charge system changes the last time I updated it, mostly "improved diagnostic ability" stuff