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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.

The 3-valve's variable cam timing is the engine's other weak spot. The cam phasers and their VCT actuators wear and the timing-chain tensioners and guides loosen, producing a loud rattle or tick that is worst on a cold start and at idle -- owners repeatedly describe the engine as "sounding like a diesel." Left alone it progresses to phaser or tensioner failure and, in the worst cases, a replacement engine. Dealers typically diagnose cam phasers, VCT solenoids, and lifters, and the repair is a multi-thousand-dollar top-end job. Like the spark-plug defects this was handled as a known-issue / TSB matter, not a recall.

Check — Start the engine stone cold and listen for a rattle or diesel-like tick in the first few seconds and at idle; a persistent noise points to worn phasers or timing components. Ask whether the phasers, tensioners, or timing chains have already been replaced. A 5.4L that starts quiet and has documented maintenance is fine -- but this repair is expensive once the noise sets in.