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.

A second, separate spark-plug problem is specific to the 3-valve engine: its long two-piece plugs carbon-seize in the cylinder head and shear apart when removed, leaving the lower half stuck in the bore. Owners report a dealer breaking most or all of the eight plugs during a routine change and adding a per-plug extraction fee, turning a basic tune-up into a job quoted from several hundred to a few thousand dollars. Ford acknowledged it with a special removal-procedure bulletin (TSB 10021048, "Spark Plug Removal Instructions - 5.4 3V") that calls for soaking the plugs and using a dedicated extraction tool; there is no recall.

Check — Ask for records showing the plugs were changed with the soak-and-special-tool procedure, and ideally that upgraded one-piece service plugs were installed. If the vehicle is at or past the ~100k plug interval on its original plugs, budget for a slow, careful plug change and the real chance of a broken plug or two.