custom 404 overides for codeigniter so we can just call "show_404('say something')" anywhere from the code, put this file in application/core, still need to edit $route['404_override'] = 'welcome/error_404'; in config/routes.php and create valid controller or nasty error will appear when browse to false url

MY_Exceptions.php

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class MY_Exceptions extends CI_Exceptions {

  public function __construct()
	{
		parent::__construct();
	}

	function show_404($message = "The page you requested was not found.")
	{
		set_status_header(404);
	
		if (ob_get_level() > $this->ob_level + 1)
		{
			ob_end_flush();
		}
		ob_start();
    
    // 1. load codeigniter to get any data (optional)
  	$ci =& get_instance();
    
    // 2. set any data for template to display (optional)    
		$data['message'] = $message;
    
    // 3. get the content from view and set to the master template variables (optional)
		$template['partials']['navigation'] = $ci->load->view('partials/navigation', $data, true);
		$template['body'] = $ci->load->view('partials/errors/error_404', $data, true);
		$template['partials']['footer'] = $ci->load->view('partials/footer', $data, true);
    
    // 4. put the master template on memory
		include(APPPATH.'views/layouts/home.php');
		$buffer = ob_get_contents();
		ob_end_clean();
		exit( $buffer );		
	}

}