BUY WITH CARE

The 5.4L Triton's headline failure is a spark plug blowing clean out of the cylinder head. The aluminum heads hold each plug with only a few threads, so a plug can strip those threads and eject under compression -- owners report a loud pop while driving, sudden rough running and a misfire, and a repair that runs from a steel thread insert (Time-Sert / Heli-Coil) per hole up to head removal, commonly quoted between several hundred and a few thousand dollars. Ford never recalled it; the fix is documented only in TSBs on repairing spark-plug hole threads in aluminum heads (609650, 6090435). The same modular-V8 architecture and defect are shared with the 4.6L and 6.8L, so on the engine-mixed 2004-2010 F-150 the complaint texts that name a blown or ejected plug are the reliable signal, not the engine badge.

Check — Ask whether any head has already had a steel thread insert installed (a prior one-hole blowout repair is common and not disqualifying if done properly) and whether all eight plugs seat and come out clean. If the original plugs have never been serviced near the ~100k interval, budget for the repair and treat an open history of "sounds fine" with caution.