Rebuilt injectors. As far as i know they do not have a specific tune for dw. They prefer to deal with known good injectors. I have tuned several cars with dw and can assure you that you need to adjust both the k value and latency for them to work perfectly. I find it hard to believe z1 does not know about the latency adjustment thats required.
That being said i have not had good luck with the newer batches of dw