heres the run down. 89 xj 4.o auto 4WD "RENIX" pretty much stock. driving it down the interstate and it just loses power... no noise no indication of problems just suddenly loses power ( did not cut off)and when you try to make it go it starts to backfire and hesitate.... removed the cat.. cleaned and tested the injectors. installed a new cps, tps, the plugs and wires and caps all less than 3 months old. installed a fuel pump and fuel pressure reg. now it s running like a dream... no hesitation no pops smooth and strong.. O Happy day

Except it is way too loud so I have a new tail pipe and muffler installed

.... Now it starts ok and runs smooth as silk for about 5 minutes then it starts to hesitate and backfire through the throttle body. but only under load during acceleration. I found out that if I turn the engine off and then restart is is ok again for a couple of minute then it returns to acting up..... it idles fine and revs smoothly in place. 31 psi on fuel rail. 40 with vacum removed. So its not the pump again

... where do I go from here ............ ? coil o2 sensor, distributor what is next....