Hi: My 98 Explorer's "service engine" light came on, and the vehicle was running rough. The Ford dealership service technician said the code is 304. I have looked at the below website but do not see a 304. Does anyone know at a code 304 is? Thanks http://www.therangerstation.com/3digitcodes.html PS: I have been told probably either have a blown head gasket or cracked head. See "Cracked head or am I being took?" thread.