I have a 1999 Jeep Cherokee with a 4.0. It cranks but won't start. Replaced the crankshaft position sensor, throttle positioning sensor, ignition coil, and the battery. I have no idea what else it could be. Any ideas?

 

Do you have fuel pressure (~40 psi)? You can check the fuel injector plugs with a "noid light"

Same for spark - do you have spark? Check with a spark tester, or put a spark plug in one of the wires and touch it to the engine block to complete the ground. Should have a good blue spark.

 

Def check for fuel pressure at rail with gauge. Can you hear the fuel pump run when you turn the key on? Check for 5v reference signal at each of those sensors with key on. When did this start happening? Has it ever started since this happened? Did it die while running then wouldn't start or simply wouldn't start one day?

 

pickup coil (camshaft positioning sensor)

 

^^^THIS.

Do not throw any more parts at it. You need to adopt a "testing based strategy" to determine root cause.

1. Check fuel pressure (must be done with a gauge) The spec for your 98 is 49 psi, plus or minus 5 psi. Parts stores rent fuel pressure gauges.
2. Test for spark. Looking for a strong BLUE snapping spark
3. Be sure that your fuel injectors are firing (noid light)

Good luck and keep us updated!