1997 jeep cherokee 4.0 help?

could just one bad fuel injector make a straight six run bad? popping and sputtering and not wanting to run good? but sometimes it runs good and then it does'nt, i have given it pretty much a full tuneup, but it still acts up. how do I know if a fuel injector is bad when the check engine light went off? please help my poor sick jeep..thanks everybody for all your great help, Mick