Are you a shop for private individual? Just to make sure that you are aware the even numbered cylinders are on the passenger side or passenger bank. This being said have you run a compression test on the passenger side cylinders? How many miles are on the vehicle? have you checked for intake leaks or has there ever been any other malfunction codes set other than the misfire codes?
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Yes if you have a known issue with a o2 sensor or air fuel ratio sensor on bank 2 then this can definately cause a misfire across that bank of the engine, those are primary sensors that control air fuel mixture as well.
Once this is addressed if you still have an issue I would check the timing belt position on this side of the engine, it is possible that the timing belt could have jumped one tooth to cause the timing to be thrown off on this side.
I have replaced the O2 Sensors and I still have the problem with cylinders 2,4,6,8 misfiring.