2000 Jeep Cherokee Hydraulic Valve lifter

With only 80K on the engine changing one lifter or changing them all is a toss up. If it were a 180K, it would be a "no brainer" not to change them all. Problem is, which one is making the noise. You could pull the valve covers, let it sit over night, and look for a loose rocker, but you may find several that are just a little loose. A full set aren't that high buck. You might want to play it safe, and change them all. If you decide to change the set, be sure to soak them face up in oil for a while, until they stop bubbleing, and use a good engine assembly lube. Also, you want to check the bottom of each lifter for scoreing from the cam. Hope this helps.