Periodically, my 2003 150 superscrew with 4.6L starts miss firing, the check engine light obviously comes on when this happens. Took it to the Ford Dealership and Big-O-Tire and they both told me that it it #1 spark plug that misfires. Big-o-tire has taken the #1 plug out a couple of times to drain water that comes on there and take the plug out to clean. This seems to happen when it rains and water gets on there. My truck has just over plus 100,000 miles and I had already had the tuneup. All the plugs were brand new. The #1 plug that periodically gets water around becomes rusted. Any suggestions on the water issue or overall.Thx

 

Weird that number 1 plug would get rain on it. Are your sure that it isn't a slight coolant leak either from the Tstat or intake area?

 

Have you ever changed the COP plug boot? They can take set from heat and not seal properly when reinstalled after a plug change. That will allow road splash into the plug well and may start a misfire condition. Install a new boot and spread just a little dielectric grease inside the boot that slides over the spark plug. Don't fill the boot with grease, you don't want dielectric grease on the spark plug's terminal to COP's coil spring contact.