Turning on VSync in the game is pretty easy.
First, you need to open notepad and chose Open from the File menu, then navi to your Documents directory, which is located under the Users > yourusername folders.
In the Documents you will find Call of Juarez - The Cartel > out > Settings folders (> symbol means that you have to open these folders).
On the first sight Settings folder appears empty, but fear not - in the notepad switch *.txt option in the drop-down menu to the All Files (*.*), and then you will see two files Audio.scr and Video.scr - open the second one.
Under the GrassQuality(0) option add VSync() and save the file, but please, do not try to remove exclamation ! mark from the VSync() option above - this option will be ignored and overwritten on the game start.

1. Start Notepad
2. Open Documents
3. Open Call of Juarez - The Cartel > out > Settings
4. Open Video.scr
5. Add VSync() below all the lines
6. Save the file.

I hope this guide will be helpful for you.