misfire that won't go away..

[Dead Eye]

If its specific to one cylinder then I doubt its a fuel issues, sounds more like a spark issue to me.

What did you replace? All the plugs, all the leads, both?

If you replaced only the plugs then I'd suggest its probably the lead to cylinder 4 - the coil pack should be fine if no other cylinder is having issues (there are 2 packs which control 2 cylinders each). Best thing to try is to take the cap off the plug and the lead, trim a few mm off the end and replace the cap and see if it helps.