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The 4.6L 3V and 5.4L 3V variable cam timing (VCT) feature may emit a light knock in normal operation and is audible only at idle speed, with a hot engine (gear selector in park / neutral). However, it may be masked by or mistaken for other noises generated from either injector firing or a malfunctioning valve train as described above. The noise does not affect performance or durability of the part.
VCT phasers may knock at hot idle. It may be heard inside the passenger compartment, or the wheel well area. Some light noise is normal. The engine may require a cold soak overnight for a full diagnosis to effectively be made at hot idle, particularly when a VCT phaser is suspected. The knock is not prevalent at cold temperature.
If the noise intensity is more than a lightly audible knock at hot idle under 1200 RPM at engine operating temperature, replace the cam phaser