I've got a 98 Cherokee 4.0 automatic that continues to miss and backfire intermidily, so far I've put the acell tune up kit which has wires, plugs cap and rotor, ran some fuel injector cleaner and some sea foam through the fuel system, replaced the throttle pos sensor and the crankcase sensor. I need to get this fixed so I can sell it, Ive bought too many toys and this one has to go

Thanks

 

You should verify proper fuel delivery. Backfiring is often caused by an imbalance in the fuel/air ratio so fuel pressure should be ruled either in or out. Must be done with a fuel pressure gauge hooked up to the schrader valve on the fuel rail.

For a 98, the factory spec is 49 psi, plus or minus 5 psi.

If fuel pressure checks out, test your MAP sensor. It too is involved in determining fuel/air ratio. There is a vacuum line leading to that sensor; be sure that the vacuum line is pulling good vacuum. You'll need a manual and a meter to test the MAP sensor.