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Low RPM Reading

by Charles J. Norris in 912 / 914 Technical Questions 3 years ago

912ULS w/ GRT EIS 4000. Tach is reading lower than engine RPM. Normal take-off power. At a low cruise speed reading, tach reading 1200rpm low.

Re: Low RPM Reading

by Kevin Stewart » 3 years ago

Kevin Stewart

3 411 1.24k

You don't say whether this is a new fault or whether it has always been like this. Is it a new or existing installation?

I see that there is an addendum to the EIS manual for Rotax 912 connection, see here:

https://grtavionics.com/media/912-M2000-4000-Addendum.pdf

The troubleshooting guide also has these words of wisdom:

Rotax 912/914 : On about 1 engine in 10, the tach reading from the dedicated tach output will be erratic. This is
cured by reversing the two tach output wires from the engine, or installed a 10k Ohm resistor (1/4 W or larger)
inline in the tachometer lead.

https://grtavionics.com/media/Troubleshooting-Guide.pdf

Thank you said by: RotaxOwner Admin, James N Parker

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Re: Low RPM Reading

by James Ott » 3 years ago

James Ott

22 334 392

Many folks have had to install the resistor to cure erratic tach readings, sometimes after several hundred hours of trouble free use.

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