89 Jeep wrangler runs rich

How is your o2 sensor? if it is bad it would make the car run rich and foul the plugs.

double posted, now adds rich but not the actual DTC number
sadly.
why not post real numbers.
we work best with hard facts not interpretations. ...

case in pont
mike uses ford book to look up jeep DTCs.
he fails.

the condensor if it has one if the electronic module thats normally mounted under the coil

did you check the air filter? if the air filter is dirty, the mixture is automatic richer than normal. the ratio between air/fuel is changed.
try this ant let us know.

It sounds like your new crank sensor is defective. It should be under warranty.

you check for miss how is compression

a bad sensior on the thottle body

4.0 is an L 6 . Not having the luxury of being there and doing the necessary testing myself, you will need to do that. You will need to get either a chilton or haynes basic manual and a decent digital volt/ohmeter. things I'd immediately check are the map sensor, manifold temperature sensor and finally, remove and visually inspect the fuel injectors (can test good electrically but be fouled on ends, causing a poor spray pattern). These are suggestions only...I would not replace any of these without testing.
Any questions about specific items, just ask!!
Good luck

One possible explanation for this is that the crankshaft position sensor is going bad.

Have you checked the tightness and/or tried replacing the alternator/drive belt? I have an 89 cherokee and I had the excat same problem .. I replaced my alternator drivebelt and wala .. fixed .. Crayz