Livn,
Still having the problem.
I didn't see a 3rd ground on the rear of the driver side head and I havn't had a chance to trace the ground for the fuel injector rail. Things are pretty tight in there and everything is wrapped up tight in black tape, it won't be easy without having to remove some items on the top of the engine to get a good look. Although the car is running ok, the strobing is annoying!!! plus I do feel it, slightly, when accelerating. There are maybe a few minutes where it stops doing it, then just comes back.
Are you having this problem still?