Changing a 4.0L and 4.2L starter
Turn the key...clunk.
Even worse is when you turn the key and absolutely nothing happens. You can fiddle with the Crankshaft Position Sensor all you want, or hook up jumper cables but that won't work. First of all, since the motor didn't turn at all the CPS isn't at fault. It's not the battery either, so what else could prevent the motor from turning over?
Odds are that the starter is frozen up. Mine started acting up toward the end of last year, and I quickly learned to leave a hammer within reach of the driver's seat. When I would turn the key and get absolutely no sound in response it was time to crawl underneath and give the starter a couple of whacks to un-sieze it. In the last week or so though, it didn't even respond to multiple percussive maintenance attempts so I knew it was time to change it out.
The location and general technique is the same for almost all 4.0L and 4.2L (258cid) Jeep engines used in the CJ, YJ, XJ, MJ, ZJ, TJ, LJ, WJ, and other models. That motor in various configurations has been a Jeep powerplant for more than 40 years, and the starter has always been in the same spot. Bolt sizes may change, and connectors may vary but the general principle is the same for changing the starter.
Disconnect your battery, Negative (-) side first.
Locate the starter
This is the starter for most Cherokee XJ 4.0L engines. This one happens to be from an early Renix model, but it fits my High-Output 4.0L just the same.
This is a (relatively) clean starter
Of course, that info is no good without knowing just where to look for your starter. This picture is taken from the front of the Jeep, near the passenger-side front wheel. I am looking up along the frame and can see the oil filter at top center in the picture.
The starter is circled in the middle of this photo
Removal and Replacement Removing the starter meant first removing the wire loom coming down from the (+) side of the battery. In my case, this meant removing a 9/16" and 5/16" nut from the starter and simply pulling the wires away. After that, there are only two bolts holding the starter in place; one from behind the starter and one in front. For some bizarre reason, one was 14mm while the other was 15mm - I don't recall which was which right now though...
Replacement is the reverse of removal. Without the added time taken to snap pictures, this job is a pretty simple one and can be completed in less than an hour.
My starter replacement was also a great opportunity to notice I've got problems - the starter lobe on the bellhousing is cracked and just moved to the front of my "must repair" list.