It's the crank sensor!
Join Date: Nov 2007
Location: Central Minnesota
The fact that the engine was partially frozen, the subsequent overheat and now you have driveability symptoms is most likely not a coincidence.
You most likely have some engine damage here. If you're lucky, you had an overheat because of a frozen cooling system and it blew your head gasket or cracked your head. Cross your fingers that the block is okay.
Irregardless, it is time for some testing. Start with a simple compression test.
Spec for the 4.0 is 120-150 psi, with no more than a 30 psi variation between cylinders.
And as you know now, I would never leave plain water in your XJ. 50-50 is a good mix for the majority of people's applications.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!