I have 2001 navigator with 5.4 Intek engine and all four cylinders on the driver side are not firing what could this be ?

 

There's no such thing as a "5.4 Intek" engine in a Navigator.

 

Since each cylinder has it's own fuel injector and ignition coil you be looking for something common between them, like a broken wire. If those 4 cylinders are not getting fuel then follow the red fuel injector wire. If they are not getting spark then follow the red/light green COP wire.