I recently started having a random misfire on cylinder 1, pulled the plug which has around 30k miles on it and compared to the new motorcraft sp546. Anybody else having the sp515 plugs crap out around 30k miles?

 

515 was replaced with 546 because reports of out of the box failures.

 

I figure it was more the blue weld joint failing and causing porcelain to crack near there . The sp546 is really beefed up on the tip and done differently . Be sure and clean out hole with carb cleaner to not break plugs going in ,that carbon build up is tough stuff . I went to champion after the first plug failures . Never had a problem , I have a box of 515's to give away I almost put them in but the comments on the forum saved me . . Champions are double platinum -- none of the others are . They do a wring off test that sold me .

 

Mine looked like that at 40K. The electrode tips were gone.