Congrats your purchase of a WJ 4.0. Mine just hit 147k...yep....It's not the smoothest engine, but it's damn near bullet proof.
Here is a tip about a common issue that causes misfires, hesitation, bucking electrical shorts etc...Check it out during your next tune-up to save future headaches:
Carefully check the fuel injector wiring harness; follow it from the front of the valve cover to the rear of the engine....There is a cylinder head stud/bolt head at the very back of the engine (drivers side behind valve cover) this stud/bolt head rubs through the harness, short circuits the wires and causes rough idle, bucking, misfires, hesitation and random codes. The symptoms sometimes begin after the engine is hot or has been running on the highway for awhile, and often come and go...It will take more than just a quick visual inspection....If the harness is resting upon this stud (or near it for that matter), if you don't allready have this problem eventually you will. I repaired the wire, wrapped the entire in harness in nylon loom, and put piece of vacuum hose over that stud...problems solved...
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