1998 cherokee 4.0. Vehicle has seat for 3 years. Tried to get it started and was crank no start. Installed spare ecm from a 2002 cherokee. Vehicle now starts but mifires on cylinders 2-5. Confirmed fuel system is ok. No spark on those cylinders. Replaced cap, rotor, plugs, wires, crank sensor, and cap and rotor again to verify. At idle spark from coil looks fairly consistant.

 

Are you sure that the spare computer from a 2002 is the correct application for your 1998?

I'm not sure but it very well may not be the right application and if not, that could be the cause of the spark/cylinder issue you are having.