I am currently testing a similar concept just using a knox sensor on my scope. 1. For vehicle vibration and 2 I also have to deal with Gates Poly Chain tension. Still working out the offsets to make it work. Open to suggestions if anyone has any, or feel free to R&D (rip-off and duplicate) LOL.

You could do a relative compression test with an amp clamp that would at least let you know they were all firing the same.

The C7 engines were also known for the fuel pressure regulator on the back of the head failing open so they would not build fuel pressure because the return side was stuck open. Might be useful to check for air in the fuel on the supply or return fuel sides as well. Could have a bad injector o-ring ...