Some 2018-2019 Lincoln Navigator vehicles built on or before April 8, 2019, may exhibit a ticking/tapping or rattle noise from the front cover area of the engine on initial startup after a cold soak of 6 hours or more that may last for 2-5 seconds.
This may be due to a worn variable cam timing (VCT) unit. To correct the condition, replace the VCT unit and update the PCM calibration with revised VCT parameters. Replace all four VCT units.
