EGT reading over range

[RVDan]

On my Skyview, I have a single EGT probe that is reading over range and X'd until the engine is started, then it looks normal.  If I disconnect the probe the reading shows low (but not X'd). 

I have swapped probes and the problem moves with the probe, so I have a probe problem, but it seems like an odd failure.  An open probe results in a low reading.  I am not aware of a thermocouple failure that can drive the channel excessively high at ambient temps and act normal with elevated temps.  I can duplicate the problem with the probe isolated from ground and heating the probe with a torch, so no odd grounding issues.  These are Dynon probes. Nothing else is on in the aircraft except Skyview so that somewhat limits potential EMI issues.

Any ideas?

 

[Dynon]

Nothing is immediately coming to mind. Like you said, it sounds like an odd degradation of the probe. When in this condition, what do you see under EMS SETUP > SENSOR DEBUG DATA for this EGT. What does one of your normal ones say?

 

[RVDan]

Thanks, will check that out.