Alternator Charging Issues with a Twist

[Darkbloodmon]

03 H.O. 6MT 230.8K

Was running some scrap to the recyclery last Friday. Dropped the load and upon pulling away noticed the engine vibration was off, and my idle was higher at a grand. Quick glance at my gauges and volt meter is reading 12v. I pull over to the nearest gas station and confirm that the gauge was reading correctly with the truck running. Batteries weren't taking a charge, both reading at 12.5v. I had a few other stops to make on the way home. I cut the truck off for those stops, and upon cranking it back up, voltage dropped to 8 then bumped up to 12 on the way back home. The check gauges light was illuminated for my return home, the battery light never illuminated.

I was putting her on ramps since I figured I wouldn't be moving reliably for a while and had some major parts going in. Pulling on to the ramps, Voltage was nominal on the gauge, did a voltage drop test, and checked the alternator power cables, case, terminal as well as the connections on the cables. Everything was nominal.

Maintenance notes: Grounds and power had been previously cleaned less than 6 months ago. I re- cleaned all the grounds and power connections except for the one ground behind the engine to the firewall. I'll get that when I pull the trans for the clutch.

Batteries are Mopar flavored lead acid cell, MFG March of 2017. I maintain my batteries meticulously the tops are clean, cells topped, terminals corrosion free. Even now as they sit disconnected in my truck they are both reading 12.5v after nearly a week of sitting.

Alternator is OEM from the factory 230.8K, bearings are creaky but upon test the alternator is still putting out demanded voltage. This test was replicated multiple times with the same results.

My cables are old and not as tight on the ground side for the battery terminals, but the voltage drop test didn't indicate anything abnormal.

No codes, but I can double check, I know most of the soft ones floating around.

Thoughts?

 

[IH8CALI]

My cables are old and not as tight on the ground side for the battery terminals

I can't comment to the alternator specifically, but I will say one of the best improvements i've made to two trucks now, is the customer battery cables. I think you can buy straight from Geno's now, I can't remember the company name I purchased from in the past. Regardless, the cables are impressive and absolutely worth it.

 

[GCroyle]

Not a direct diagnosis but might be worth visual insp.

My ALT passed a bench test on machine but didn't charge in truck. Slip ring was worn. It shows as a black ring deeply cut compared to worn brass looking.

 

[Doc Holiday]

I just put new cables on my 2003 from custombatterycables.com. I bought the 3/0 winter upgrade, the alternator cable and the grid heater relay wiring upgrade. Not inexpensive but having installed them they are very well worth the cost. The only other thing to maybe investigate is the voltage regulator. There is a company that makes an external regulator ECM bypass kit if that's what you find the issue to be. I bought the kit as the next step in case the cables didn't work.

 

[AH64ID]

I’d see about getting your alternator rebuilt. Worn brushes and/or slipring can give you those symptoms.

Since both batteries are at the same voltage it doesn’t seem to be a crossover cable issue.

 

[Tuesdak]

As noted... common for worn brushes "sticking" and you hit a bump to unstuck it. Loose battery connection on alt (or elsewhere) is also possible.

 

[Darkbloodmon]

Thanks for the input, I'll follow up when I get my truck back together, it's been one thing after another recently.

 

[Doc Holiday]

I

Thanks for the input, I'll follow up when I get my truck back together, it's been one thing after another recently.

I understand how that feels...