So, my new-to-me 5.9 has been doing a weird charging/no-charging thing. I had some posts on it in my general questions thread here --> http://www.jeepforum.com/forum/f13/n...tions-1533877/
, but I want to pull this one item out into a separate thread.
Here was how I described the issue in the other thread:
Charging system - after a few days of working fine, my charging systen seems to have fritzed out on me. Driving along today, all good, suddenly my volt gauge goes to ZERO, and "check battery" begins flashing on the VIC. Still running fine, as are all the electrical items like lights, e-fan, etc. I make it back home, about 10 miles, with no drama. Now, in the driveway, it will start up, gauge reads about 10 volts or so for a minute +/-, and then it drops to zero, and check battery message. I cleaned terminals, and checked cables, they look okay.
And, after some suggestions, I updated with ths:
So, today I went down to the local FLAPS and had them do the battery test. Battery tested fine. So, since it's so damn easy to do, I pulled the alternator right there in the parking lot and took it inside so they could mount in in their testing rig. Good news/bad news is that it tested perfect. Good news, because, hey, I don't need an alternator. Bad news, cause that means I move on to the next likely fail point. I guess it's the PCM now, right?
Later, I discovered I had new symptoms, here:
If I start the Jeep and the volt gauge jumps up to about 14, it will be fine until I turn the ignition off, no matter if I drive 1 mile or 10 miles. If I start the Jeep, and the volt meter goes up to just a hair over 12, in less than half a mile, the volt gauge drops suddenly to zero concurrent with warning chimes and "Check Battery" on the VIC. Jeep will keep running, at least for a while. I really haven't pushed this too far. New thing to add here is that I plugged a cigarette lighter volt meter in, and watched it as the Jeep malfunctioned. In the case where it starts off barely above 12V, when the chimes/alarms/VIC go off, the voltage actually sometimes jumps to 13.7 or 13.8 volts. Most of the time, it doesn't, it just hovers around 12V.
Okay, so now I have new info. I feel like a detective circling his prey. Today I'm working on the Jeep, and I remembered my Dad would sometimes tap on electrical components and sometimes it would work. So, opened up the hood, positioned a voltmeter plugged into the cigarette lighter where I could see it from under the hood (it's attached to a 4 foot cord) and started using a short piece of rebar to tap on things. Not too hard, just a tap. So, engine running, voltmeter reads 12.1V
- Tapped on PCM connectors. no change
- Tapped on battery terminals, no change
- Tapped on black plastic box on top wire of alternator, BINGO
Whn I tapped on that black box, the voltage meter immediately jumped up to 13.7, AND the sound of the alternator immediately changed. It went from making no discernible noise to a slight whine or whirring sound.
So, what is this magic little box?
Does it need replacing, or does my alternator need replacing?
Because the alternator had tested good, I tended to think the problem was something else, but now I'm not so sure.