99 4.0 problems

[99tjsahara]

I have a 99 wrangler with 4.0 and straight drive tranny. I'm having problems with the engine when I crank it up I does fine and I go down the road about 15% trottle and it starts breaking up and loses all power and back firing its like u were going down the road and u cut the motor off.I don't know if its throught the intake or exhaust. I would say exhaust. But if I give it WOT it goes again but this has boggled my mind for too long now. I don't have any check engine lights.