The bolt can have loctite on it, or a little siezed from corrosion over the years, sometime a strap wrench or pry on the starter teeth won't hold it still enough to break the bolt free.
Never done it on an XJ, on a mini-van with an automatic, I tried everything, finally went and took the vehicle to someone with an AIR IMPACT Wrench, that took it out for me, THEN we put it back in and torqued it lightly, it was good enough to drive it home and go back to work, this time able to remove the crank bolt with hand tools.