I am getting bad gas mile on a 2005 ford tarus how can i tell if it the fuel injection going bad

When was last time you had a tuneup ? Check air filter and replace if necessary, clean throttle with throttle body cleaner, add fuel injector cleaner to gas tank and replace fuel filter.

If check engine light is on have the codes read at a local auto parts store. This service is usually free. Post the codes here and we will see if we can help.