RPM Unstable

[badia358]

I have the Dynon Skyview Classic which was installed in 2013. Over the years the RPM reading has become unstable and it spikes between 3000 to 5000 RPM when at full throttle. It had worked good at the start of 2013.

I have a LASAR ignition with the RPM lines connected to EMS 37 Pin Connector Pin 32 & Pin 33. Since this is an electronic ignition and the RPM lines are not directly from the mags, should I be connecting the RPM lines of the ignition module to EMS 37 Pin Connector Pin 34 & 35?

Thank you...

 

[Dynon]

From other threads here (I couldn't quickly find their documentation), it looks like they output a pulse in the 7-8V range, which would indicate using the low voltage pins (34/35). But if the voltage wasn't enough to register (this was an issue with the D120/D180 if you search the forum), you'd expect to lose RPM, not see spikes. Is there a signal for each ignition source? IE, can you flip back and forth between left and right and see any difference in the two?

 

[badia358]

The way that it is connected today (pin 32 & 33) has a single for each line. The mag check work wells and shows a good RPM. I mainly see the issue of showing higher RPM when at full throttle. I will see it happen every once in a while during cruse at 2200 RPM.

I have not tried the low voltage pins (34 & 35) yet and was wondering if I should try them or is there something else that I should do.

 

[badia358]

Yes, it has a signal for each line. I wrote single by mistake.

 

[Dynon]

So we don't have a great explanation for what you're seeing. Noise on the otherwise unconnected RPM inputs could cause isssues, although tracking down the source of that might be tough. You could start by making sure that there aren't any loose or intermittent wires going into those pins. But you also could try switching to the lower voltage inputs, which may not change things, could improve them, or could make the effect worse. Another thing to try, when you're actually seeing the behavior, is to try to tie it to one of the mags (by shutting them off one at a time). It could be that the ignition system isn't outputting a clean signal anymore.

 

[badia358]

Did not think of the ignition system no longer providing a clean signal. So I will check for this next time that I go flying. I did think that noise could be the cause here, but a little harder to debug.

One more question since I would like to have a reliable RPM reading 100% of the time. Is there a transducer that I can use to pick up the RPM from the mag?

 

[preid]

The only way I have been able to resolve this over the same time period is to replace the resistor to reduce the noise, it resolved the issue for about 2 years than I did it again and it worked about the same amount of time. never knew the resistor could lose its resistance over time, but the fact that a new resistor resolved the high RPM tells me it must be related somehow.

 

[jabarr]

Did you happen to measure the old resistor to actually see if the value changed?

 

[badia358]

I have not checked the old resistor, but will do it this weekend. It worked great for about 3 years and then the unstability started and it has been getting worse. So will replace the old resistor and give it a try.

Thank you...

 

[Dynon]

Is there a transducer that I can use to pick up the RPM from the mag?

And alternative is the IE VTACHGEN 2 that you can find on this page

 

[vlittle]

Let me chime in.  I am not sure it applies to the LASAR mags, but I have been recording and diagnosing ignition waveforms for a few years.  One thing I have picked up is that any degradation in spark plugs or spark plug wiring can lead to erratic (spurious high rpm at high power) indications when using P-lead or hall effect pick ups.

The first step is to clean, check resistance, and carefully gap the plugs.  That's cheap and easy to do before tearing into the rest of the system.

Vern

 

[badia358]

First, let me thank everyone for their help and input.

Here is what I ended up doing. The LASAR ignition has an Optional Tachometer wire (Brown wire). I connected the LASAR ignition Optional Tachometer Brown wire to the Skyview EMS D37 connector Pin 34 & 35 (Low Voltage RPM).

I have to do more flying/testing, but it is working at this point.