Put it in 4wd (or what you think is 4wd) find a nice patch of grass, and hammer down.
If you have one skid mark in the grass, it's not in 4wd. If you have two skid marks, then it's in 4wd.
I know nothing about jimmies. Was about to exit out of this forum, and never return, but decided to help someone out.
I don't know what kind of axles jimmys have, or if they're equipped with LSDs or lockers in them, but if you have two marks in the grass in the back, and one in the front, then you most likely have an LSD in the rear.
Should of bought a jeep.