Just finished installing new plugs and plug wires.
The Ranger ran fine when parked on Monday. On Tuesday morning, it had a stumble on idle, which got worse and tripped the CEL. The code was for cylinder 4 misfire.
By freak chance, some parts I had ordered for installation for the 200,000–mile service arrived that morning from Rock Auto, including new Denso plugs and Motorcraft wires. I began installing both yesterday afternoon, knocked off when I got fatigued and the bugs got bad, and finished this morning. As I went, I sprayed the old plugs with Kroil, then with CRC Freeze-Off, especially on the passenger's side where access was tight.
The old plugs were Denso and could still have gone at least another 10,000 miles. The No. 4 plug wire had burned through because of contact with the exhaust manifold, causing the misfire.
The Ranger is running well so far. I had disconnected the battery near the end of the work to reset the CEL, and it's staying off so far. The engine seems to be running a bit smoother than before the problem, so the plug wire was probably becoming a problem long before it finally failed. The new No. 4 wire has been rerouted to keep it away from the manifold.
Ford really made changing plugs on this engine a pain, but I got it done. My hands and arms are tired and sore, but I'm getting older too.