Most certainly Ch A current clamp is detecting the operation of injector 1 (Ch B) via inductance
Given injector 4 was switched off, we now have this circuit behaving like an antenna in which the current clamp senses a number of high frequency “switching” events (i.e. other injectors)
Resting the current clamp on top of the engine (not around a cable) near injector 4 may also produce similar results
What is interesting is how defined injector 1 appears in the wiring for injector 4. This is most probably due to the arrangement of injector switching circuit within the ECU or injector driver assembly
Image 1
The image above is how the signal would look (Ch A) using the COP probe resting on Injector 4
The COP probe being a capacitive pick up device, the current clamp is an inductive pick up device
Often injectors 1 and 4 are companion injectors for companion cylinders and may share a common power supply between them, so presenting an increased level of induced voltage to the current clamp about injector 4 wiring.
This may or may not be the case; it could simply be that the wiring for injector 1 and 4 run alongside one another within the engine harness, where there is a capacitive link between these cables
Below we can see how the current clamp around injector 4 wiring also detects other injection events but with a lower amplitude due to reduced signal strength
Image 2
Such a response from a current clamp could be interpreted as "noise", yet how useful is "noise" in this scenario as we can detect other injection events using a single current clamp on one scope channel