You can cut it off without grounding anything but of course the auto tune function of the EM2 will not work without the O2 sensor input.   The mixture indicator on EM2 will drift around unless you ground it.  This is one example of where you can usually parallel two instruments from one sensor and it will work.   Mixture monitors just look at voltage from the sensor and are usually very high input impedance so they should not load down the sensor.

 

BTW Buly, when I looked at your EC2 map table prior to the snubber update it was VERY erratic.  I was surprised the engine ran well enough to fly.  Take a look at it with your EM2 and make sure it looks reasonable after you do some tuning. 

 

  For instance, if two adjacent MAP addresses are at opposite ends of the scale, it is not reasonable and you should investigate.   It is very instructive to fly with the MAP table screen up on the EM2 in track mode and watch the table pointer (blinking bargraph bar) and the mixture monitor.  Move the throttle around so that the pointer moves through the suspected problem areas and insure that the mixture monitor stays in the middle. If it doesn't, adjust the MAP address that causes mixture to go out of proper range. 

 

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