Originally Posted by SonicVQ

Now that you have a scope, I think the next step is determine bad coil, vs bad wire/ecu.

Set up the scope and get a screen capture (use phone if there isn't a built in function) of cylinder #4 signal wire and either #2 or #6 ignition coil.

Move ignition coil #4 to #2 or #6, and take screen shots again.

Compare the pictures and see if the lower voltage signal wire moves to #2 or #6 or stays on #4. (posting the pictures would also be helpful to me)

• If the low voltage signal moves with the coil, I would suspect a bad coil.
•*If the low voltage signal stays on cylinder #4:
• check coil ground and 12volt supply

Since the original problem got worse after changing the plugs, I would focus on the wiring and check connectors for burnt or bent pins.

When checking wire resistance, it is important to keep in mind that the meter uses a very small current for the resistance test. The ignition coils uses a fairly high amperage of about 12 amps for 0.005 seconds when at idle. (I have scoped my G37's ignition coils)

This can result in the meter showing a good connection, but it may not be a good enough connection for the current draw of the coil.

Additional thought:
Over the years I have tried to help many people with car/engine problems.
About half the time, aftermarket add-ons have directly or indirectly caused the issue.
Melted wires, wires pulled too tight and break internally, loose connections, missing grounds, etc.

With this in mind, please double check any modifications that have been done looking for the items mentioned above.