Cherokee XJ Crank Position Sensor (CPS) Failure
I first heard the phrase "unconquerable misery" used by Diana while she worked on context-sensitive help for one of our software products. It describes the feeling you get while working on an intermittent auto-electrical problem.
Infrequently at first--then consistently--the XJ would crank, but not start. There was no spark at the coil. I eventually solved the problem by replacing the prone-to-fail crank position sensor (CPS). The CPS's propensity to fail is well known. What is not well known is that many times it's the connector which fails, not the sensor itself. Before buying a new CPS, try unplugging and re-plugging the connection a few times. If that seems to help, bypass the connection permanently by soldering the wires. The local (reputable) Jeep dealer says that this technique (soldering) has been "standard operating procedure" for years now.
The CPS is located on the driver's side bell housing behind the engine. The connector is located above the engine near the throttle body.
It goes without saying that I spent a massive amount of time gathering this information. At the same time--to add insult to injury--I foolishly purchased a Jacobs electronic ignition system in an attempt to improve my Cherokee's modest performance and poor starting characteristics. I have learned my lesson and will now pay penance by warning all unsuspecting buyers away from The Danger.