Its a 2000 xj with 130k miles. The problems started with after I turn it off it would "short out" if I tried to start, when I say short out literally as soon as I turn the ignition all power would disappear. Jump it and it runs, then all of a sudden the voltage skyrockets to 19v. Turn it off, shorts out. Jump it take it home, switch batteries to one I had sitting around. Truck starts try to pull off dies, battery won't hold voltage. Leave it a few days. Come back to it, jump it and it only stays running if I have gas applied if not dies even with jumper cables attached. So I pull alternator, get it tested it passes fine. Reinstalled everything back, run truck with a direct jump no battery runs fine. Connect battery runs but gauge says 0 volts. Wtf!? Drive truck it runs then all of a sudden dies. Go to start it battery loses voltage, jump it and it won't stay running unless I'm pressing the gas keeps dieing out, it was doing this before I pulled the alternator as well. Finally it runs far enough to get home. Notice belt is squeaking so I thighten the pulley and it runs. One thing I noticed is one of the times I was jumping it, it was running fine as soon as I pull the cables off it dies. I start it no jump and it starts fine just out of curiosity I touch the jumper cables to the battery and it sparks and dies. Now it starts and runs but voltage is at like 11 volts. I did test this battery and guy said it had been drained past zero so he couldn't tell if it was good or bad. Not sure what that means?

Anybody have any idea what this crazy problem could be, I'm at a loss right now. I know it's running but if I take it out again I'm sure it will strand me.

Can it be a belt issue? Belt is squeaking under load and I know PO was messing with the belt day before I got the truck. It ran fine for a week before this.

 

Have the battery load tested. The PCM goes stupid when the battery dies and you have to keep your foot on the gas until the PCM relearns the correct idle position. I think the battery is the root cause of your problem.

 

Thanks for the feedback, yes I believe both these batteries I have may be trash but the other weird symptoms baffle me.

 

Low voltage and crap batteries cause a lot of weird issues. When dealing with strange electrical problems always start at the battery.

 

The next step with weird electrical issues would be to go over all your ground and electrical connection, in your case especially the starting circuit.
Clean all ground connections in engine bay shiny and snug 'em back up tight.
Clean your battery cable connections
Check your fuses for completeness.

As Busted said, start with the battery. Have it load tested or if its an old one, do yourself a fav and go for a good and reliable new one. Even if the above is not solving the problem, it's good maintenance.

Report back and

 

I think very often WEIRD=GROUND

 

True, once you confirm the condition of the battery the grounds would be the second place to look.

 

Thanks guys, I'm going to start tracing all the power and ground cables to see if there is any damage or corrosion.

 

I have to agree with what the others have said. Your grounding points are your battery terminals, battery to fender, oil dipstick, rear of the head to fire wall, 2 one the coil and the mounting area between the starter and the engine block. Take a piece of sandpaper or a wire brush to each of the connections and make sure that they are nice and shinny. Let us know how everything turns out.