Crawl under your XJ, on the top rod from the tc lever running down to the torque bar there is a block of metal with a bolt in it. The block is the trunnion, the bolt is the locking bolt. Loosen the bolt.
Crawl out from under your XJ and open the driver's door. Remove the tc lever shift bezel--the plastic piece with the markings on it. Move the tc lever all the way rearward to the rear shift gate. Place a 3mm (1/8") spacer between the lever and the shift gate. Secure the lever in place with a bungee cord so that the lever remains tight against the spacer.
The part is not listed, but number 1 points to the grommet that goes in it. Once you are sure that it is fully engaged in 4lo, then tighten the locking bolt in trunnion on the upper rod, remove the space and bungee cord, replace the bezel.