Heh, very gallant of you, but I don't know much at all. However, and color me surprised, I've now learned about noid lights from
this article, so I'm a bit less clueless than I was yesterday, yay (although the same article also says an oscilloscope is the best injector troubleshooting tool)
About the grounds question, I just don't see how any common/shared ground that is not specific to an injector bank could cause a whole bank, but nothing else, to fail. Did you check X161 thoroughly? I can't yet dismiss the idea that it isn't seated properly or has some damage, it would be such an obvious explanation.
Unfortunately I'm not familiar with ECM internals, maybe it does have bank separated grounding on its circuit board, but at that point your only realistic choice is ECM replacement anyway.