I have a 1999 Ford Ranger 4x4 Auto 4L. In the past 2 months I've had it in the shop for engine misfire issues. Both times the truck would start to miss some, then progress to loss or partial loss of one cylinder firing. At that point the check engine light would come on. My local dealer worked on it both times and got codes for cylinder 3 misfire the first time and cylinder 4 the 2nd time a month later. They replaced the plug both times and it fixed the problem (at least temporarily). They said the plugs both times look fine, no cracks, no black spots, no smell of flooding or unburned gas. They have no clue what is causing it. The truck was just tuned up less than a year ago, with all of the plugs replaced with motocraft plugs. When I asked what the hell was going on here, they were honest enough to tell me they have no clue, and had never seen this before. I said what about just changing the other 4 plugs in case they were all defective and they said they had never experience a lot of plugs being bad and didn't want to do unnecessary work at my cost. I guess I can carry an extra plug and change them one at a time if it starts to miss. I'm tired of paying $87 for a spark plug every month Any ideas on what could be happening, or what to check?

 

I have a similar problem with my 2000 4.0L. it tends to eat plugs on the number one cylinder and some times the number 4. The plugs from those cylinders look the same as all the other plugs in the still working cylinders. "Bosh 2" plugs seem to last the longest for me about 7 to 10 months. All plug wires are new too.

 

get your fuel injecters checked, i had a mis in my 3rd and 4th cyl, so i replaced all my plugs, plug wires. still had a mis. so i replaced my ignition coil pack. still had a mis, so i replaced my crank sensor, then my mechanic said it might be my catts. didnt fix the problem. so i had to pay to have my codes ran and along with my cyl mis fire my injectors came up. i assume bad o rings, so im getting them fixed tomo and ill let you know if it works. (find a shop that will do the work if you get your own part, it saves $$$)

 

Not sure if you have the same problem as my friend but his is a 2000 3.0 and his was misfireing at idle so he took it to a guy he knows and it was a sensor or something was chewed into (by a rat) under the intake box...not sure if this will help you any but id check anyway