1998 Ford Ranger • 220,000 miles

I have a 1998 Ranger that, until now, ran perfectly. I went to the store, went in, 5 minutes later got in and cranked it up to hear it "missing" or something. Had the local parts store plug up their hand held diagnostic and it said it has lost ignition in # 4 cylinder. It has less than 2000 miles on this set of plugs and wires and it has spark at the coil pack. Could it be an injector and if so, can that be cleaned or do I have to get a set? Already checked, $65 each.
March 10, 2013.

Have you checked to make sure you are getting a good spark to that cylinder? Is fuel pressure within the manufacturer's specs?

I could only check with a screwdriver and it had spark on both plugs. Not a mechanic, trying to check what I can before I have to take it to one.

Mar 10, 2013.
Make sure the fuel pressure is within spec. Make sure the spark is a blue snapping spark. If they are both good, check injector to see if it is getting power. If it is, check compression in that cylinder.