Thanks Joe. After some extensive research over in the rotax forums there was some great information about calibrating the sensor (and leave it where it is). It's probably best to verify manually that the below procedure correctly calibrates the sensor, but here's what I did.
- with sensor setup as normal in the g3x config page I turned on lane A&B on the 912is and then switched on a fuel pump
- obtain the current sensor value. At this point the engine manifold pressure is the atmospheric pressure and there shouldn't be any calculations required
- switch the sensor to "use manifold pressure" and then adjust with calibration until the readout matches what you got above.
I did this a few times. So far it seems to be working. But I would still like to verify manually at the end of the fuel rail.
One thing to keep in mind is that apparently the G3X calculation will not take into account density altitude. I've read that for every 1000ft you will loose about .25 psi in the fuel pressure readout. As a result I was told to calibrate it based on your home location and normal density alt.