So I've read a bunch of threads and still don't know where to start. So It's a 99 4.0 automatic with 220k. when I start it up everything is fine and dandy. Sometimes after a few minutes idle gets rough but sometimes it stays smooth. when I put it into drive and apply gas, the voltage spikes to about 17 until it tries to shift into second gear. The dash lights get brighter with the increasing voltage so it is indeed over charging momentarily. when it tries to shift into second, it puts me into what feels as 3rd gear and keeps me there unless I restart the jeep( like a default or limp mode). if I manually shift it through 1 and 2, the voltage still spikes but goes back to 14 at 30 mph where I can put it in drive and it shifts perfectly and I have plenty of power and no voltage fluctuation. So needless to say its just happening on acceleration from a stop and voltage seems to be the reason why the trans. Goes into default mode.
now on a side note, I went to jump by buddy the other day, and I could not get ANY power from my battery to his while my jeep was running but I no the battery isn't dead cuzz I can always start my jeep and my alternator is fairly new... so that makes no sense to me. Anyways when I get a chance I will start checking everything, but I'm wondering if anybody has any ideas on where to start. thank you.

 

Clean both ends of the battery cables and surfaces they mount to.

 

^this^ also the grounding systems on our xjs arent the best in the world. Please check out 5-90's wiring upgrade for our Xjs, its well worth it.

 

Here is 5-90
https://www.cherokeeforum.com/members/5-90-711/

and this info
http://www.kelleyswip.com/electric.html

 

okay thank you