I have noticed on a number of threads that a lot you fellows have changed out your plugs well before the suggested 160,000 kilometer rating. I have 128000kms on my 05 Lariat, how do you know if you should have them changed?
Thanks Greg

 

They are changing them early in an attempt to avoid the breakage problem after carbon build up. Has nothing to do with the plug's performance. You need to use the search feature and read about the "sparkplug TSB".

 

if you have a 5.4 then you have the chance in them breaking. if you got a 4.6 then your good until fuel mileage starts to suffer or until it runs poorly.