Good to know. Still new to the 4.0. I come from the corvette world where you HAVE to improve the fuel system once you do mods more advanced than boltons.

 

Woah woah woahhhh..! You have a supercharged 4.0 that is working relatively well. That's badass! I wouldn't want to go back to stock. I would try to get more info out of the OP about the work he put into it and the struggles he went though. That could get you on the same page as him.

As far as tuning you could start by buying a Bluetooth obdii thing that will give you live readings of a/f and many other things. Then at least you know what's going on in there.

 

I would swap that engine for a good stock one any day for an XJ, more reliable for sure and less to worry about.