I would like to replace them
I can't locate the spark plugs in my express van. can you advise where they are on 2003 Mitsubishi Eclipse
What kind of 'express van' , a 2003 Mitsubishi Eclipse is what your question has listed? Spark plugs are Generally located at the end of spark plug wires in the cylinder head, or under coil packs , depending on engine/ignition type.
You must mean the Chevrolet Express...take the dog-house off and you can access the spark plugs...