Are you getting a code that says its the EGR? high flow, low flow? DPFE sensor a ford one? there have been issues with the aftermarket ones...
2001 ZX3 2.0L Zetec-
Hatch Nation #42
Going through Rebuild See "The TICK Build Thread" for details (http://www.focusfanatics.com/forum/showthread.php?t=289168&referrerid=62897)