I had an older jeep that did about the same thing u might want to see about doing a compression test on it and see if you have good compression, could be leaking around the rings. If that proves to be good i would check the pcv it could be stuck open which could bring oil straight into the intake fouling your plugs. Have u pulled your plugs yet try that first easiest way to tell what it is doing if it is burning on one cylinder or all. hopefully this will get u started and is helpful not saying it is the answer but could be a good place to start. Also u need to determine if it is gas or oil, like my old jeep i had a lot of problems but had the same thing ended up being the fuel regulator that fixed my no start problem.