* 2.0L Zetec four-cylinder: This was a very common engine in the 2004 Focus.
* 1.8L Zetec four-cylinder: A smaller displacement option also available.
* 2.3L Duratec four-cylinder: This larger engine was less common but available in some trims.
To know the exact engine size for a specific 2004 Ford Focus, you'd need to check the vehicle's identification number (VIN) or look at the engine bay itself.