Hi all, I just purchased a (new to me) 98 F-150 Step side with the 4.6L. Last week, I started getting my check engine light on so I plugged in my trusty OBD II and got back a misfire on cylinder 4. I replaced all the plugs with Bosch Platinum plugs from Pep- Boys.Also replaced the plug wires. Four days later, I'm misfiring on cylinders 1, 3, 4, and 8.
Thats when I found this web site and found out about how Fords eat Bosch plugs for breakfast. So yesterday I went down and changed out my Bosch plugs and replaced them with Motocraft plugs from the dealer.
Now my question...... When I pulled out the plugs, all were good except for #1 and #3, they were melted. Is this going to cause a problem with my motor, and what would cause my spark plugs to melt in four days?
Any and all help would be greatly appreciated. Thanks in advance.

 

Sounds like the wrong heat range on the plugs or too small of a plug gap.

 

yeah except that the motocraft plugs that I installed last night is still causing a misfire. Plugs are gapped to .052 which is in range of factory specs. Went to the dealer to ask what would cause it today and he said that he thought that the cat might be plugged up. But wouldn't that fry ALL four plugs going to that cat? I just have a hard time believing that a cat would cause this. Any help would be appreciated.

 

Are the motorcraft plugs starting to melt also?