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No Tach Reading on Right mag during mag check

Saville

Saville

Well Known Member
Hi All,

Not sure if this belongs in Engines or Electrical. It's a little of both. So I'll ask the magneto-specific questions here.

The Problem:

I have 2, Slick magnetos.

During run-up, When I check the left mag, my EFIS shows the RPM. When I go back to BOTH and then to the right mag, the RPM is displayed for an instant, then counts down to zero in less than 2 seconds and then the value is replaced with "---" on the display.

I have a TruTrak EFIS and EDM module.

Ok so I've been studying up on Magnetos, wiring, the EFIS etc.

My Question:

When you check the right mag, you ground out the left and it no longer produces a spark. So then you read the RPM running on the right mag only.

Is the rpm information that comes off the P-Lead on the left mag still there and readable even though you've grounded out that P-Lead? I assume it is as there is only one pin input for Tachomer in the EDM (Engine Data Module) connector.

thanks
 
Last edited:
Saville said:
Is the rpm information that comes off the P-Lead on the left mag still there and readable even though you've grounded out that P-Lead? I assume it is as there is only one pin input for Tachomer in the EDM (Engine Data Module) connector.
Click to expand...

No it isn't
 
PaigeHoffart said:
No it isn't
Click to expand...

Ok well then that must mean that the airplane is wired incorrectly.

As there is only one TACH input, then it seems to me that the input needs to come from the Mag switch common and not directly from the left mag P-Lead.

Is that correct?
 
Look around for a left-right switch.

The system needs a switch that will direct the tach signal to EFIS from one mag or the other.

Or better yet, contact the builder and ask him how it works. There has to be a way to check both mags.

With GRTl, there is a circuit that does this automatically.
 
David-aviator said:
Look around for a left-right switch.

The system needs a switch that will direct the tach signal to EFIS from one mag or the other.

Or better yet, contact the builder and ask him how it works. There has to be a way to check both mags.

With GRTl, there is a circuit that does this automatically.
Click to expand...

Dave,

Well yeah there's the Left-Right-Both_off key switch which you use to start the engine and check the mags.

But as I say, the TACH input to the electronics comes directly from the left mag P-Lead, and not that switch.

I'm thinking it ought to come from that switch. But I wanted to get the opinion here.
 
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