Trouble finding the cause of a misfire.
Ok so here is what im dealing with. i have an 02 jeep grand cherokee 4x4 4.0L that all of a sudden one day started to have a misfire of some sort. At the beginning of the day it ran find i had went to the gas station to get gas filled it up with 91 octane drove on into town and when into the store to get a few things. when i when to start up again the misfire started. i took it easy and got it back home and just thought that maybe i fowled a plug but when i replaced them it changed nothing. from there i tried cleaning out my injectors, still same ol thing. then i started going through a list in my head of everything that i know of that causes a misfire. all that i have replaced that i can think of is my spark plugs, injectors, coil pack, cam sensor, crank position sensor, and then i went through the whole jeep and made sure i had no open grounds. after doing all this it still have the same misfire. whats odd is that i can start it up and for the first couple seconds it is completely find then it will start to misfire, really its more of a shutter then a misfire. could this by any chance possibly have anything to do with my fuel system...fuel filter, fuel pressure, or fuel pump. please can anyone help!?!?