I'm having troubles remembering now, does cyl 1 and 4 share a coil? or is it 1&3, 2&4? Anyways, if they share the same coil, then swap the coil with the other one and see if the misfire switches cylinders. Otherwise the next step I'd check is the plug wires, these fail pretty common too. And like always, whenever you are dealing with misfires, its a good time to change the spark plugs.