5.4 3v engine loosing power at low revs
Hi please can someone help me on this,
I live in the UK and I drive a 2005 Lincoln Navigator which is fitted with the 5.4 3v engine, I do aprox 25 to 30K miles per year and change the oil and filters and transmission fluid regular. And early on this year I changed over to the Champion 7989 plugs after reading problems of the factory ones snapping off.
Over the last month the engine has become louder with a tapping noise when idling at both cold and running temperature, and it is running with a slight lumpy feel at low revs.
If im cruising and revs are between 1000 and 2500 the engine feels rough, but not miss firing just slightly off, and the power seems to have decreased, but if I floor it and drops down another geer the revs shoot up and off it goes with no problems.
I am finding that on take off, and if im accellerating up a hill, for a split second the power drops and then it feels like its struggling to pick up, but again if I floor it, it will drop to another gear and take off as normal.
Can anyone give me any tips as to what this might be, as in the UK we dont have any lincoln dealers and the ford dealers wont touch imported cars. And local garages dont want to look at it either.
Any help would be good before I resort to ripping it to bits,