D-180 Tachometer rapid fluctuation

[Closterman]

Since some flight, I have rapid fluctuation of the rpm.  The weird thing are that all are ok on one flight, and the seconf flight I have the problem... 

I have a EFII Electronic Ignition and both ECU are connected to the D-180 for the tachometer input.  I have check both wire and all look good....

 

[Closterman]

I forgot to tell that all working good for the last 3 years (240 h)..

 

[Closterman]

See the video for a better explanation of the problem :

https://www.youtube.com/watch?v=LSRR6Gts3LE&list=UU7lQNiAFyQe2FS3yD4JlhWg&index=1

 

[jakej]

IF your connections are good the I'd add a 30KoHm resistor in the rpm line to the Dynon (if you don't have 1 already) worth a try & it's very a cheap 'test'.

 

[Closterman]

I didnt have a resistor. Whats the purpose of the resistor ? From the EFII manual, the ECU give a square pulse to the Dynon. I will try to unplug 1 ECU to see what will happen, and may be found which one are faulty...

 

[jakej]

resistor is generally used as a 'fuse' for voltage output ignitions & magnetos & also has a dampening effect with ripple current.

 

[Closterman]

I have tried the resistor witout success.. I have put a 30 ohm resistor and the tachymeter doesn't work at all... Indicate 0 rpm while the engine run (at any rpm).. I have tried bigger resistor and same result...

I have also update the firmware. Didn't fix the problem..

What can I try now ??

 

[Dynon]

Do you know what the voltage of the square wave is supposed to be? Given that it once worked and now it doesn't, it sounds like the Dynon unit isn't seeing a clean signal from the ignition anymore.

 

[mmarien]

I have the same problem with my P-Mags that just showed up in since Oshkosh 2018. Nothing has changed in the wiring since I installed Skyview and P-Mags about 600 hours ago. The EMS pins 34-35 are wired to pin 6 of the P-Mags.

https://photos.app.goo.gl/45CXG6E6fnzMdPTR6

 

[Closterman]

Do you know what the voltage of the square wave is supposed to be?

From EFII, the tack signal was a 12 volt, square wave with 2 pulse per revolution..

"MMARIEN" , it's weird because it's exactly the same problem, but we have a different ignition system, and it's not the same Dynon product !! 

 

[mmarien]

Coincidental but I wonder if it has the same solution.

I tried shutting off one of the P-Mags with the P-Lead but I forgot the pulse line from the P-Mags still outputs a signal regardless. They are both to the same breaker so I can't turn one off. Even if I could, the P-Mag generates it's own power.

I disconnected one of the P-Mag tach pulse lines to the EMS and took a test flight today. There was some fluctuation but a max of 20 RPM. A couple possibilities. One would be a faulty connection or bad tach signal that I eliminated by disconnecting it. The other would be that the tach signals are slightly offset and Dynon is reading both once in a while. I'm not sure if the tach signal from the P-Mags is synchronized with the spark signal. So it's possible that the timing is correct and synchronized, but the P-Mags are outputting the tach signal slightly offset to each other. This could be something unique to electronic ignition.

 

[kurtfly]

Regarding the P-Mag tach signal it is coincident with the firing. The falling edge of tach is when the coil fires the plug. So, they both should be firing at the same time. Check your timing and check the manifold pressure connection. if one p-mag has a leak it will not advance as much.

Check your ground connection on the p-mags. A bad ground will make the tach noisy.

 

[mmarien]

Thanks Kurt. I have a couple of other squawks that point to a ground problem - all happening randomly. So your suggestion adds to the evidence that it might be a grounding problem. I'll dig a little deeper.

 

[mmarien]

A quick question. The EMS-220 has several grounds. Some are used for three wire sensors. Do any of them specifically need to be grounded to the common ground or is that taken care of with the network harness?

 

[jakej]

Just use any of the EMS grounds as THE ground for the EMS - I think pin 3 is the ‘designated’ one but it doesn’t matter as they are all connected internally.

 

[mmarien]

Thanks Jake. I just finished checking and none are connected to gnd. Will gnd one of them.

 

[mmarien]

An update.

I reconnected the right P-Mag RPM pulse that I had disconnected. I reset the timing on the two P-Mags. All the MAP sensors have a common manifold along with the P-Mags and the fuel pressure regulator. There are two gauges. The Skyview EMS gauge and the SDS EFII gauge. They agree and the MAP seems to function as it should. If there was a leak both P-Mags would be affected.

I pulled the EMS-220 37 pin DSub connection and checked continuity of the GND pins. D37p3 and D37p5 are missing. Some of the GND pins are used by three wire sensors. One of the GND pins had a solid connection to GND. I found one of the other GND wires was not connected to anything so I connected it to GND. So if there wasn't a good GND there is now.

The P-Mag tach signal (+12V) is connected to EMS D37p32/33.

The fluctuating RPM problem still exists. It only happens at high RPM.

I think I'm going to use "rpm_policy=SINGLE" and add a second RPM gauge to see if the RPM signal is the same from both P-Mags.

I'm open to other suggestions.

Correction:

D37p2 and D37p4 were missing along with a couple other wires. D37p3 wasn't connected to GND but I found the wire for D37p5 and connected it to GND as noted above.

 

[Raymo]

Also be sure the P-Mags AND the EMS is also well grounded to the engine.

 

[mmarien]

Ray. I have a brother that keeps his plane in KGVL. I landed KRBW a couple years ago. I'll look you up next time I'm down there.

I'm in contact with E-Mag on this one. I added "rpm_policy=SINGLE" and graphed the results. I also switched the harnesses. The problem seems to be the right mag as the left tach signal works fine with either harness. First graph is with left harness on right P-Mag. Second is right harness on right P-Mag. The problem follows the right P-Mag.