if you want to see a good source of auto trouble shooting information, go on Utube and look for Southmain channel.
This guy Eric runs a small shop in NY. He spends WAYYY to much time making understandable and clear videos
on auto troubleshooting using the cars he gets into his shop. When he has issues like this, he has a PICO scope that
he checks the current pulses to the plugs or injectors to help understand where and what the problems are.
His detailed trouble shooting advice is priceless.
Great guy. Learned a lot from him. Diagnose first before you shoot the 'parts cannon' at it.