D120 Pin 14 only reading 4 volts (should be 5 volts)

[blueflyer]

D120 fuel flow gauge reading erratic after 4 years of rock steady operation. I replaced the FT-60 but I still get same erratic readings. D120 EMS Pin 14 runs to the fuel flow gauge (FT-60 in this case). Pin 14 should supply 5 volts to FT-60, but I am reading a steady 4 volts coming from Pin 14. What can be done about that?

The power and ground wires to the FT-60 were also checked and found to be good.

 

[Rhino]

I don't profess to being greatly knowledgeable on the D120 or the FT-60, but what strikes me about your question is an erratic reading caused by a steady change. Ordinarily, a static change doesn't produce erratic readings, but rather a steady change in readings. It's not impossible mind you, but it seems strange. If your change in readings was steady, you might be able to adjust the K-Factor to compensate. But if they are indeed erratic, that probably wouldn't help. I'd confirm the ENGINE TYPE is set correctly as well.

Another thing that strikes me is that the FT-60 is supposed to operate on 8-30 volts. So, technically, neither 4 nor 5 should be enough. But what also strikes me is that such a wide voltage range suggests the readings should not change with a voltage change. That makes me feel the problem is inside the D120 itself, and likely not related to a difference in voltage, particularly if that voltage is steady. I would ask Dynon about that directly.

 

[RV8JD]

I don’t know either, but I was curious. Pin 15 is the power pin supplying 14V.

From the D120 install manual:

From the FT-60 Red Cube manual:

 

[blueflyer]

Thanks guys. I tend to agree with you of both. Pin 15 shows a steady 12 volts and Pin 14 shows a steady 4 volts. I have tried hooking up the voltmeter and wiggle the wires and the red cube to see if I could make either Pin 14 or 15 voltage move, but they both stayed constant. According to EI Tech support, Pin 14 should be providing steady 5 volts to the red cube. Again, like you say above, I would think a steady voltage, albeit lower than desired, would not result in erratic gauge behavior. I have an email in to Dynon tech support, but haven't heard back yet.

 

[Marc_J._Zeitlin]

Thanks guys. I tend to agree with you of both. Pin 15 shows a steady 12 volts and Pin 14 shows a steady 4 volts. I have tried hooking up the voltmeter and wiggle the wires and the red cube to see if I could make either Pin 14 or 15 voltage move, but they both stayed constant. According to EI Tech support, Pin 14 should be providing steady 5 volts to the red cube. Again, like you say above, I would think a steady voltage, albeit lower than desired, would not result in erratic gauge behavior. I have an email in to Dynon tech support, but haven't heard back yet.

I'm sorry, but I don't think you are understanding (or someone isn't) what's going on here with the "red cube". The red wire, from pin 15 on the D120, is 12V/14V power TO the red cube. The black wire from pin 13 is the ground wire TO the red cube. The yellow/white wire from pin 14 on the D120 is the OUTPUT from the red cube - it's NOT an input wire - you can't have three input wires and expect to get output of <something> to the EMS.

The yellow/white wire output FROM the red cube TO the D120 is a voltage (or current - don't recall which) dependent upon the rotational velocity of the turbine in the red cube. If you're measuring the voltage on the yellow/white wire when it's not connected to the red cube you'll get some arbitrary voltage that the EMS is sitting at on that wire, or when the red cube has no flow through but it's connected to the EMS you'll get the zero flow rate voltage.

If the flow rate is erratic, either you have a loose connection on one of the three wires, or else the red cube (or the D120, possibly) is on the fritz.

 

[blueflyer]

Thanks for that explanation. Its me who is ignorant. I'm sure the EI tech didn't say voltage from the D120, its just what I understood him to say, but what you say makes more sense. Anyway, it still doesn't change the fact that all voltages are rock solid, so I cant figure out where the problem is. I do appreciate the input. Anything helps.

 

[Marc_J._Zeitlin]

Thanks for that explanation. Its me who is ignorant. I'm sure the EI tech didn't say voltage from the D120, its just what I understood him to say, but what you say makes more sense. Anyway, it still doesn't change the fact that all voltages are rock solid, so I cant figure out where the problem is. I do appreciate the input. Anything helps.

If you have disconnected the FT-60 from the EMS and you're measuring voltage on pin 14 on the EMS, then you're just measuring some internal floating voltage that doesn't mean or represent anything in particular (although you could call Dynon's support line and ask them what it might mean - can't hurt). As I said, if the flow readings are erratic, either there's a loose/bad connection on one of the three wires or something's wrong with the FT-60 or D120. I'd suspect the FT-60 first. It's an electro-mechanical device, and electro-mechanical devices can fail.

Disconnect everything, clean all the contacts, check the wiring, and if it still acts up, swap in a new FT-60 and see if the problem goes away.

 

[blueflyer]

just to close this thread, I think I found the issue. After doing some work under the cowl, I forgot to re-secure the fuel line entering the red cube. After re-securing this fuel line at the inlet side of the red cube with its adel clamp, the erratic behavior went away. I think it was vibrating without the clamp installed and producing bubbles and the erratic readings. Thats my best guess at the moment anyway. I flew after re-installing the adel clamp and the fuel flow was rock solid.