An Accent came in for service and misfire problem. We have serviced the engine and hoped that the new plugs will fix the problem. But after starting the engine the misfire was still there. I have unplugged the coils one by one to listen to any difference in engine idling and I could hear that no 3 coil was not firing always. I actually remove the coil from the spark plug and plug into it another old plug. I have earth the body of the plug and start the engine. The coil was firing perfectly. I then pull out Pico scope to check all four coils current and no 3 injector to see if there is something going on with either the coils or no 3 injector. See the image below the blue line is injector voltage and the red line is the current of the coils. All looks ok to me.
My next step was to remove the coil from the car and test it with my homemade coil tester to see if I can see any problem with it. See the video below, sparks jump out at the side of the coil. When the coil is pushed down onto the plug the spark would jump out to the metal sleeve wherein the coil is hosted.