Do the primary injectors batch fire? Seems an obvious NO, but I've swapped front primary and rear primary wires at the ECU, and the car idles at the same speed and has the same AFR as it did in the stock configuration. Talking at idle speed up to 3800rpms, as to whether they batch fire or fire sequential.

 

I have a buddy who had a primary wire crap out, so he piggy backed both primaries together. So now they are batch firing. Still running the stock ECU, no mods. So far he has not noticed any issues at all. HP, MPGS, everything the same. So it doesn't seem to matter if they batch fire or not.