Using session name in PHP - Cannot Access Data

Question

When I use:

session_name( 'fObj' );
session_start();
_SESSION['foo'] = 'bar';

Subsequently loading the page and running:

session_start();
print_r( _SESSION );

do not return the session data.

If I remove the session_name(); it works fine.

Does anyone know how to use sessions with a different session name?