I have 94 Cherokee sport 4.0 h.o. developed a mis. it does have a good crack in the weld in the header. I replaced plugs, dis cap and button, also installed ford stang 5.0 injectors and new fuel pressure valve. still have mis, is it because of crack in header or something else. need help tired of spending cash. I have had this jeep for 7 years and just started running like crap after I noticed crack in header. didn't think the loss of back pressure would make it run like crap.

 

Plug wires not replaced?