I have the same problem with mine. It churns for about 5-10 seconds before firing up. I read elsewhere within this forum, that it could be down to leaky injectors dribbling fuel into the chambers while the engine is stood. It was suggested, as a temporary fix, to disconnect the power supply to the cold start valve. This has improved starting quite a bit. So my problem could be due to leaky injectors.
I am now in the process of trying to find the cause of my problem.
Hope this helps somewhat, but I doubt it, as you have already replaced your injectors. I will keep you informed of any advancements
into the root of my problem.
BTW, did you replace your injectors with new ones, and if so where did you get them and how much are they for a set?