[eluser]cyoarte[/eluser]
You don't need to enable cache query on config/database.php.
If you set TRUE cache query on config/database.php ALL the queries are by default cached.
If you only want to cache specific queries set FALSE cache query on config/database.php and then you need to write $this->db->cache_on() before the query and this cached all the queries after that on the same function of the model (only on the function).
If your function have multiple queries and you dont want that all was cached write $this->db->cache_on() before the queries you want to cache and write this->db->cache_off() before the queries you don't want to cache.
Important is that you set the cache directory on config/database.php with the full path of the server.
(Sorry by my english, I'm spanish)