Download Some 1999-2004 Navigator, 2002-2003 Blackwood, 2003-2005 Aviator, 2003-2004 Marauder and 2003-2004 Mustang vehicles built before 12/19/2004 equipped with 4.6L 4V/5.4 4V engine may exhibit a runs rough, lacks power, and engine misfire, prompted by a MIL light and DTC codes P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, and P0316. ACTION Diagnose engine for engine misfire concern. If diagnostics determine an engine misfire which is characterized by leakage through exhaust valve(s), only replace the affected cylinder head(s). SERVICE PROCEDURE FOR VEHICLES WITH RUNS ROUGH/MISFIRE CONDITION: 1. Perform relative compression check on all cylinders. If abnormal, check cylinder leakage and actual compression for “low” cylinders refer to Workshop Manual (WSM), Section 303-00.