The chemicals can help, but there is only one way to thoroughly clean the injectors.

Get some old fashioned, caustic, soak the parts overnight type carburetor cleaner. Take the injectors apart and soak them overnight in this stuff. You may need to do them one at a time or whateve method necessary to keep from mixing up the parts. You want all the same parts from an injector to go back together only with that injector.

Good luck,