evoman

I have a 2000 gc with the 4.0 and my check gauges light is on and the voltage gauge is on 9. Voltmeter on the battery says alternator starts charging at 13.6 v and rapidly climbs up to 18ish v. My lights start to flicker on the dash, the jeep is running so bad it can't pull its own weight. Why is my gauge saying nine but my alternator is clearly overpowering? Bad regulator I would think but idk since the gauge is acting strange. I have cleaned the alternator and battery connections well and checked belt tension and cleaned the engine grounds. No change. Any help would be appreciated!

Cherokee_Mike

Are you saying the battery reads 9v with the engine switched off ?
I had a similar problem with poor running and low voltage - dead cell in the battery causing a low & unstable voltage - new battery cured it.
Try a known good battery to see if that makes a difference.

dave1123

Yes, battery. I had a similar problem with one of my cars. I had just driven it about 20 miles to look at a motorcycle for sale. When I went to leave, I turned the key to start and heard a BANG from under the hood. All my electrics went dead. Opening the hood, both the big battery fill caps had blown off. It started with a jump but the voltage shot up to 18 volts! I turned on the high beam headlights and the heater fan to max and it went down to 16. After I got it home, I probed the cells by sticking the leads down into the acid. 2.2, 2.2, ZIP, 2.2 etc. A cell connector had shorted and set the hydrogen off. A new battery cured the problem.