Installing new Kavlico Oil Pressure Sensor to D120

[Ramizzan]

I recently purchased and installed a Kavlico 150psi Oil pressure sensor #103757. Installed on a Rotax 912 ULS to a Dynon D120. My airplane is a Czechsport Sport Cruiser. When running the engine, the oil pressure reads almost exactly 25 psi lower than it should. When checking the oil pressure with a mechanical gauge it reads exactly where it should for 912 (40 - 50). After a few weeks of troubleshooting this and ruling everything else out, I had Dynon send us a replacement unit, but it also behaved exactly the same.

https://dynonavionics.com/includes/guides/Addendum_Kavlico_Sensors-Rev_E.pdf

Installed the required 6.8 ohm resistor inline on the green wire. (shipped with the sensor).
Properly grounded to the D120.
Using sensor type 5 on the D120 settings.

Today, I measured the voltages from the Kavlico green wire at different pressure readings from the Dynon D120 while the engine was running. This is what I was getting:

1.37v reads 0psi (this is with the engine off)
2.05v reads 15psi
2.10v reads18psi
2.16 reads 20psi (Here it should be reading 45 to 50psi)
I'm wondering if these readings match with Kavlico's specs for the unit and if the D120 is expecting these voltages.
So it's behaving consistently, just consistently low. At this point, I am very suspect of the 6.8 ohm resistor that we were instructed to install inline on the green wire. I'm wondering if the addendum that I shared the link to above is not accurate? Or, maybe you only need the resistor when using this sensor for fuel pressure? If so it's not clear in the documentation. Has anyone had this experience? Starting to get desperate.

 

[Dynon]

Sounds like you have everything installed correctly. You might measure the resistance on the resistor. It's included as you say, so it should be right.

 

[Ramizzan]

Update... It wasn't the installed 6.8R resistor.

In the 2011 Sport Cruisers, they install a little terminal block on the D120 rack to be an interface between the wires coming from the engine sensors and the D120. I discovered on the bottom of this terminal there is a tiny 200R resistor installed at the oil pressure sensor connection. It was extremely hard to see based on the way the terminal was mounted. This accounted for exactly -0.4v that I was losing and the resultant low pressure reading. I bypassed this resistor and now all is well. (sigh). So the problem was indeed a resistor, just not the one I installed. It was a much bigger one I didn't know about!

Here's how you can verify proper voltage is coming to the D120 from this particular Kavlico sensor:

• Test voltage on the green wire from the sensor when it's disconnected from the D120 with the master power on. It should be reading 0.5 volts.
• Then test voltage from the green wire while it is connected to the D120 (white/yellow pin 6), at the connection point. It should be reading 1.8 volts @ 0psi. If it's reading anything else, there's a resistor somewhere! (I was initially reading 1.4v when that hidden resistor was in play).

Hope this helps folks in the future, and thank you Dynon support for being patient with me.