EIS Tach fluctuation issues

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Joined: Tue Mar 12, 2013 1:05 am

EIS Tach fluctuation issues

Post by scooter »

I have intermittent runup tach readings on an IO-360 with dual slick mags, both Tach 1 and Tach 2 wired through 27K resistors.

I have verified the wiring, checked the resistor values, removed the resistor spade plugs and soldered the resistors in, changed plugs and recently installed an optical tach on the dash.

I see a variation of hundreds of RPM at runup on the EIS data - it does not show on the optical tach. I have verified the P-lead wiring and grounding when switching mags.

I have tried both H and L filtering in the EIS setup and only L is usable - H results in fluctuations all the time.

In the air - all is well on both mags and always has been.

I'm in the process of gathering log data on both ground and in-air mag checks to see what happens to the tach signals, but I thought I'd ask if anyone has any more ideas.

I belive this to be a sensor issue and not an actual RPM fluctuation as it doesn't show on the optical tach or the seat of the pants.

Scott E
26 Hrs in Phase 1!
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Re: EIS Tach fluctuation issues

Post by GRTBen »


If you are seeing the fluctuations in the RPM during run up RPM it is likely an interference. Try adding a 10K ohm 1/2watt 5% resistor in the line. this may drop the signal to the point you would need to use the high sensitivity setting on the EIS. it may clear things up.
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Re: EIS Tach fluctuation issues

Post by lwheat2083 »

I have been trying to get the tach input working on a previously working EIS. I changed the factory alternator to the CAMIT alternator. Originally had the tach input connected to one side of the alternator output from the stock Jabiru alternator. After the changeover, changed the input to the EIS to one of the output levels of the Camit alternator BUT the pulse rep was too high for the EIS pulse count to read. Installed a divide by ten circuit and very erratic output-from 200 to 3560 indicated at steady RPM. Next tried the resistor to the P Lead - again very erratic output, pretty much the same as the divide by ten counter. Next tried using an inductive pickup-like the tiny tach uses-on the coil input to the distributor. This time no indication what so ever, I am out of ideas. Apparently there is a later version of mine that has a tach sense setting which my unit does not possess. ANY help!!! would be greatly appreciated. Cheers, Larry N853LW J250 Moses Lake, Washington
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Joined: Tue Mar 12, 2013 12:52 am

Re: EIS Tach fluctuation issues

Post by JimB »


Looks like your new alternator is a standard ND unit so connection to it won't generate a tach signal.

You now have an unused lighting coil, which was previously used as the "alternator". So connect it as shown in the manual, bottom right corner of figure 7a, Spare Lighting Coil. That is, ground one of the lighting coil wires and connect the other to the EIS.

Jim Butcher
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