Strange Charging Problem - 1992 XJ

Hi,
I have a 1992 Cherokee, 4.0, manual transmission.


So about a month ago my check engine light comes on and I'm getting code 41 (Alternator field control circuit open or shorted). I check the voltage on my alternator and battery and they looked good. I forget exactly what they were but they didn't look bad from what I've read.


So I've been scratching my head on this for a month. The light goes on for a while then off for a while and I keep checking voltages and it always looks fine. Also when this started I started getting a lot or spark plug noise on my FM radio. I'm due for registration smog check anyways so this week I bought spark plugs, wires, cap & rotor.


2 days ago my battery was dead in the morning so I put it on a charger over night and it's fine. I drive it for the day and do a battery check by turning off the Jeep, turn on the headlights for 2 minutes, turn them off and read the voltage. I think it was at 12.79 or something. Then I leave my multi-meter connected and crank the starter. It didn't drop below 10 volts, so I'm OK. Still I clean the battery posts and cable connectors.



So tonight it took a new turn. I'm driving home at dusk, it's running fine but the check engine light is on (of course) and suddenly the radio dies. I look at the voltage gauge and it's at zero (0 volts). Oh sh*t! So I turn off my headlights hoping this will help me get it home. Then I notice that my RPM gauge is at zero (0 RPM) and starts jumping around, zero then jerks up and back to zero. My radio comes back on for a minute then off again. Both the radio and RPM gauge are freaking like this, the voltage gauge is at a steady 0 volts, the engine seems to be running fine and it kind of seems like when I revved up the motor that things tried to come back a little. And it looked like even my speedometer was jerking around a bit.


I drove like this for about 2 miles then suddenly my voltage gauge comes back to standard charging voltage again. Good and steady at about 14 volts. I turn on the headlight and everything is fine now until I got home (about a mile). When I got home I checked the serpentine belt and it feels good. I crawl under can wiggle the wires to the alternator and they feel OK.


Right now my battery reads 12.86 volts with the engine off and 14.1 volts running. My engine codes are 12, 41 and 55.


So is this the alternator going bad, some voltage regulator or computer or just bad karma for the way I treated my ex?


Thanks
Marc

Oh, and we changed the clutch about 6 months ago. My son and his friend did a lot of the work and I put most of it back together so there is a chance that someone missed a motor/transmission grounding cable somewhere or maybe something wasn't tightened enough.


I didn't see the option to edit my post so I had to reply to my own post like a lunatic. But I'm really a very stable person...

You should always suspect the most recent repairs or modifications when new symptoms pop up, however the symptoms described would make me suspect the alternator.

Typically if the dashboard gauge shows 0-9 volts there is an alternator issues, usually worn out brushes. If the dashboard gauge shows 16-19 volts there is usually a wiring or wire connection issue.

Worn brushes can easily get stuck and cause a loss of charging. A bump in the road, stopping and restarting the engine, or removing the alternator for testing can knock the brushes loose and normal charging resumes.

Remove the alternator and inspect the brushes. Have the alternator and battery Load Tested. Do not rely upon handheld testers that often pass marginal alternator/batteries, the testing should be done inside a test machine.

You should also perform basic trouble shooting of the start and charge systems. Remove, inspect, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, wire brush until clean and shiny the cable/wire ends and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds.

Have a look at the fuses and terminals in the fusebox under the dash. If the previous clutch cylinder was leaking and getting into the fuses, that can eat of the terminals. I had the same symptoms, dash and/or lights would stop working while driving until I lightly tapped the fusebox with my left foot. A bad ignition switch could also cause these symptoms.