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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.