My local Mazda dealership mechanics couldn't figure this problem out. I've been experiencing misfires on the #3 cylinder for a couple years now. While the car was still under warranty, they would just replace spark plugs and coils, then the car would be fine for a time. I think the last year it was under warranty, I had it in 4 times for the exact same issue. They eventually swapped the #3 coil and plug with one of the other 3 in the car and the misfires continued on #3. Then they replaced the air intake, but it still happened again. The check engine light came on and #3 cylinder misfired again. While working on the car with a friend, we pulled the power harness from the front of the #3 COP, and then he realized he didn't have the tools he needed, so we plugged it back in. I started the car to go home, and the previous sputtering/misfires had gone away. Later that day, my check engine light also turned off. So, it turns out that every time Mazda was replacing spark plugs and coils, the only thing that was really fixing the problem was them unplugging the power from the #3 COP, and then plugging it back in again. Since then, misfires would happen every about 2 to 3 times a year. I unplug the power from the #3 COP and it would fix it every time. I've tried just moving the wires near the plastic connector a bit when this happens, just in case something was loose, but the only thing that ever seemed to "fix" it was to unplug and plug it back in again. So, that brings me to this week. I've had misfires the last several days in a row, and my previous workaround is not working anymore. Is this something I can fix myself?
It sounds to me like you have a wire connector issue with the ignition coil pins. The male and female sides fit too loose and only make partial contact. After driving a while a small amount of corrosion forms in the connection and causes the misfire. As soon as you disconnect and reconnect it the connection was made again so it would work for a while. The coil may have failed due to excessive resistance from the corrosion in the connector, and this is most likely what has happened now. I suggest you have the vehicle scanned again. If the failure was #3, then replace the coil and connector. You should also try and put stabilant 22 in all the coil connectors before reconnecting them. The stabilant 22 will stop any corrosion and help keep a full connection. A certified mechanic from YourMechanic can inspect your misfiring issue at your home or office.
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