How to you debug blank pages?

[eluser]CheekyGeek[/eluser]
I've been working with CodeIgniter almost nonstop for the last couple of days and really like what I'm seeing in theory (and in tutorials, etc.). Had things working well when I was using just Controllers and Views, but now that I'm trying to use a Model, I'm back to confused and doing something wrong.

I had a problem with logging errors, due to the webserver user not having proper permissions on system/logs, so fixed that. My hope was that I would get some debugging information in the logs. The only errors I got had to do with not being able to fopen system/cache so I also gave the webserver user permissions to it. Now there is nothing getting written there, even when I get a blank page.

So I assumed that I need to turn on display_errors in my php.ini file. But even after turning that on (with error_reporting set to E_ALL) I get nothing.

How in the heck do you debug a blank page with no feedback of any kind? There must be something I don't have configured correctly so I can see where things are breaking. Anybody wanna throw me a bone?