I have a missfire on cylinder 3. I have swapped the coil from cylinder 6 and 3, but the missfire remains on cylinder 3.
I have also done the following: - replaced all spark plugs. - checked the wiring harness resistance all the way back to the controller.
I have access to a good scope and current probe.
This is the current waveform at idle of a good cylinder. The trace has 15 seconds of persistence, to show consistency in the waveform.
This is the current and voltage waveform of the bad cylinder. The trace also has 15 seconds of persistence.
The voltage waveform in the above shot is attenuated, but shows the noise involved.
Notes: - no DTC is set with the miss-fires - no miss-fire felt at idle (above shots are taken at idle). It is worst at about 1600 RPM in 6th gear. - This is a 2010 mazda CX9, it has dual spark ignition below 1500 rpm. - The Fuel injector on this cylinder was bad and replaced. - Intake manifold gasket was replaced. - intake was de-carboned.
Am I looking at a bad engine controller?