G1000 Tachometer has the hiccups

[Robert C.]

On my last flight while climbing through 4000ft the Tach on the G1000 MFD started spiking from 2550rpm to overspeed and back, flickering between the true rpm and overspeed several times a second. It did so until in the descent when it magically stopped. Same happened on the return flight.

The engine sounded like everything was fine and the backup Tach meter that comes with the 310hp STC was rock steady at 2550rpm.

So I'm confident this is an indicator/sensor/wire/G1000 problem and not an engine issue. My AP concurs.

Yesterday we took the cowling off and checked the connectors going from the magneto to the firewall and found them tight, without play and without any visual indication of a problem. So that leaves us with a head scratcher. I'll fly again tomorrow and see if the fiddling with the wires and connectors solved the faulty indication but would be (pleasantly) surprised if it did.

Has anyone seen this or have any ideas?

Thanks in advance.

Robert

[Jeff_S]

I assume the non-G1000 tach (which is actually the primary for our planes) was fine? (Oh, just re-read your post and I see that it was.) If so, and the wires all looked good, then your transducer for the G1000 tach may be going bad. Might need an avionics specialist to work on that. Let us know what you find out!

[carusoam]

Search around MS regarding that rpm transducer for the g1000.  There may be some history on it... (some of it good)

Best regards,

-a-

[StevenL757]

Jeff, would that be an interface to his (and yours) GEA71 (airframe and engine computer)?

[Jeff_S]

Yes, correct, the GEA 71 connects all those engine and airframe inputs into the system, but I don't have a service manual (no wrench monkey here!) so I don't know what part actually measures the RPM for the G1000 readout. I suppose it's possible that it's even the GEA 71 at fault but if all the other gauges are working fine I think more likely the transducer. In my experience, it takes a pretty sophisticated A/P to know how the G1000 works, even an MSC, which is why I suggested perhaps an avionics shop.

[StevenL757]

Actually, this sounds like the Tach pickup (as I think Anthony pointed out).  3 wires coming off the left magneto on the Ovation3 GX, if memory serves.  Robert - your avionics shop (not sure who you use up there) should be able to resolve this easily.

Steve

[Robert C.]

Thanks guys. Just returned from today's flights.

we unplugged and re plugged the tach pickup from the magneto and the problem did not recur today. Then again, I stayed below 5000ft and flew at lower rpm and speed in the bumpy weather we had.

Tuesday I'm scheduled for several longer and hopefully higher flights and we'll know more.

Robert

[buddy]

Robert check the 3 connectors again, I had the same problem with mine a while back and found one of the wires was just held in the connector by a strand. Give the wires a tug at the connector and see if one pulls out, they are not the greatest connectors.

Buddy

[PaulM]

I had mine fail/(knocked) during an oil change last year..  The pickup on the mag is very delicate and had to be re-soldered.   I suspect that the strain relief is holding the wire in place but electrically the bonding is dodgy. 

[Robert C.]

So, added 5 hrs to the logbook yesterday in 3 flights that got me up to 9000ft for extended periods of time, WOT, different rpm settings. Problem has gone away

Seems like unplugging and replugging the wires coming from the mag did the trick.

Thank you for all your input.

Robert

[carusoam]

Ahhh, the power of MS...!

Thanks for sharing the solution.

Best regards,

-a-