How to troubleshoot code in a model?

[eluser]35mm[/eluser]
As I can't echo stuff out from a controller, how do I troubleshoot it?

I've just been building a login system. As it involves calls to the database then creation of sessions and cookies and then more calls to the database, I've put it all in one model and that model reports either true or false back to the controller. Laying it out that way seemed logical to me.

The login system isn't working. No errors, just telling me I'm entering an incorrect username/password - which of course I'm not! Usually I'd move an echo around to different places to narrow down where the issue is, but with CI I obviously can't do that. So how can I get output from the model so I can debug?