I have a Gem 612 in my Twinco, and recently it will intermittantly (of course) show constantly changing values for ALL paramaters. Temps will jump from -70 to 300 , voltage is all over the place, fuel flows everwhere, and then it suddenly will start working normally. I did check the airplane voltage on my Garmin and with a volt meter in the cigarette lighter and it is Stavle. Tapping the face of the unit makes no difference. I did notice that one of the CHT probes will remain eratic after the unit returns to normal. Could one bad probe (shorting out?) cause the whole unit to malfunction? Any suggestions? Thanks, Jerry.

Sounds like a bad ground or possibly noise generated by an ignition wire or spark plug with the ground shield failing.

Ditto Jim's comment

If you are using one of the adapters that plugs into the CHT hole and allows you to use the factory CHT spark plug, then I would disonnect that connection and run the engine. The people in the previous posts are probably correct and I have found the CHT adapter to be the culprit.

Regards

jvb

Thanks, I will try the above and let you know.

I noticed on the last flight that the #3 CHT on the roght engine would dance around. There is a splice in the wiring and the heat shrink around the probe wire had slipped to where the ground wire encircling the wire to the probe looked like it could make intermittant contact. I pukked the ground sheath away from the splice and put electrical tape around the splice. Now I will see what happens the next time I fly. Jerry