I have a 2002 F-150 5.4L. A few weeks ago #8 plug blew out when I started it in my driveway. I re threaded the plug and put on new coil. Truck ran great. A week later, #7 blew out. Again, the plug threaded, no problem, new coil and truck ran great. Three days later, #8 blows again. This time a new plug will not thread. After talking to some friends, and some research on You Tube, this seems to be a very common problem. So common, there are several kits available to fix this without pulling the head. I used Fix-a-Thred #98140T, about $150.00. I re tapped 7 and 8, new plug and was off smiling. The next day, #3 blew out. I have decided to park it, and re thread the remaining six. I ordered all new coils,( 8 Pack, Summit Racing #ACC-140032-8, $189.95), and all new plugs. I ordered extra thread inserts from Auto Zone #FIX98149P, about $30.00. Because the threads on the blown plugs were rusted, I chalk this one up to moisture, heat, expansion and contraction. I plan on using red thread locker on outer threads of insert, and a thread sealer on inner threads. By the way, this all started when I pressure washed my motor for the first time. Any advice would be greatly apprecieated.
The kit I mentioned are also steel inserts, not helicoils. I just finished about 30 min ago tapping the remaining six, and threading in new inserts and plugs. Just waiting on a new set of coils from Accel. And again, all the threads on the plugs were rusted bad. Hmmm.....
Because the threads on the blown plugs were rusted, I chalk this one up to moisture, heat, expansion and contraction.
Sounds like the vehicle was not maintained properly and neglected. The rusted threads on the plugs that blew was more than likely there because they were loose and backing out for a while before they blew. There was probably warning signs (exhaust leak noise) warning the plugs were backed out. Probably all started because the last person or the person before them screwed up a smile plug change.