Tach sensor issue - G3X

I have an RV-6 with Garmin's G3X in the panel. My tach sensor is the type that screws into the vent hole on my mag (Bendix, in my case).

Recently, every time I start up cold, my tach reads zero. The first time it happened I played with different RPM's and fiddled, and finally concluded it wasn't working and was about to shut down, when it instantly came on-line. I went for a flight and it was rock solid reading from taxi to shutdown. It seems to do this every time I start now. Delay of a minute or so, then reads solidly. In one hot start after refuelling, it read instantly upon startup.

Any ideas?

No ideas but I do have a spare sensor for the G3X and bendix mag I would sell cheap!

Check for a loose connection in your harness. most of the time when I have a sensor issue, it turns out to be an intermittent connection not the sensor.

Ironflight said:

Check for a loose connection in your harness. most of the time when I have a sensor issue, it turns out to be an intermittent connection not the sensor.

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I hear you Paul, and that was my first thought as well. I'm just confused with the fact that after a minute or two it is instantly rock solid. I never lost an RPM reading in over 8 hours home from Osh. It only occurs on startup, and only cold starts at that. I've had sensor issues due to connection problems, and it was evident at higher RPM / vibration levels. This doesn't seem to be acting the same.

Hello JV,

Short of connecting a scope and seeing what the signal looks like the first minute when RPM is missing, we are also not sure of a good way to chase this down.

It seems that changing out the sensor is the next step since you are pretty sure it isn't a harness connection problem.

I had to change out a magneto on my plane this weekend that went bad on my Oshkosh trip and I was sure careful to rotate the mag and not the sensor when moving the sensor from the old mag to the new mag. The way the cable enters the potting material at the top of that sensor without a strain relief makes me real nervous every time I have to touch it.

Call or email if we can help.

Thanks,
Steve