Primarily for general aviation discussion, but other aviation topics are also welcome.
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By marioair
I’ve noticed that the RPM gauge bounces around at low RPM recently.

It’s stable above 2000/when in flight

On the ground, One of the cylinders on the EDM did spike but when i switched the EDM off and on again then we're all normal again and the EDM/JPI and checks all normal.

Power checks all seem normal.

However the RPM gauge continues to bounce around at low RPM

Dodgy/loose RPM cable or sign of engine trouble?
By johnm
All I can think of is a plug or plug lead. Normally they fail at high RPM but it could be resistance causing a misfire?
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By Smaragd
Is the bouncing of the gauge matched by an audible change in actual rpm? What's the frequency of the bounce? Is it regular or intermittent? Does the frequency of bounce increase as rpm increases?
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By IainD
If its cable driven then probably rounded ends causing it to slip. Had the same
issue and replaced cable and all back to normal
T67M liked this
Mechanical tachometer then.

A shas been mentioned, check cable ends for rounding off.

Next step, have the tacho looked at.

I had a similar issue some time back. A replacement cable sorted it. I opted for a universal lay cable which will happily rotate in either direction without harm.
marioair liked this
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By gaxor
Our (TB10) Tacho uses a hall effect sensor on the crank shaft. Sometimes if it gets dirty it can result in loss of signal to the tacho pick-up sensor., or a loose connection on the sensor to tacho lead. (I seem to remember on ours a "wiggle" of the lead fixed it)