Dynon EGT Probe Reads High When Tight

Replaced one EGT probe today and all is good when hanging in free air (reads ambient- matches the other 5). Bending wire all along length and at probe and connection points shows stable, correct readings. Insertion into pipe and loose fitting of clamp also shows all good. However, as soon as the clamp is snugged up, EGT goes to 850 ish.

Sounds like a bad probe with a return to Spruce, but just wanted to check with the group for any similar experience before I do that.

Ok, so it's a ground issue. As soon as the probe makes a good airframe ground, EGT goes to 800+. This happens with 2 brand new Dynon probes. I can duplicate the behavior with the old (vm1000) probes by grounding one leg of the wire. It seems unlikely that two new Dynons are shorted internally, but how can K type probes from different manufacturers behave differently? Weird.

There are 2 types- grounded & ungrounded probes, VMS used ungrounded.

Ok. Thats something to think about but the EMS these VMS probes feed is a D180....

Anyway, I found the issue and it was a tough one: turns out the strain relief saddle clamp thing within the DB25 backshell (PLASTIC backshell) found a miniscule wear spot on the probe wire. This created a path from the wire, saddle clamp, chrome plating on the backshell, to the connector body, and ultimately to chassis ground.

Original probe back installed and all is good again. Two new Dynon probes in the toolbox.