Fuel Pressure with Engine/fuel Pump Off

[N74846]

I have been experiencing high operational fuel pressure indications for a while (7.0+ psi). I recently read a post about indicated pressure with the engine and pump off, and sure enough, my SV indicates 3.0 psi with everything off, 5.3 with pump on, and 7+ with the engine running. Is there a way to 'zero out' with the erroneous ghost pressure? I think it is more an SV issue, though I will put a pressure gauge on the line to confirm pressures as well.

 

[skysailor]

Do you have the legacy fuel pressure sender? I had this issue. The solution was to change to the new style (Kavlico) sender. Now all is well. Just had to lead the 5V power out to it from the EMS since the new senders have three wires instead of two. The ground and sense wires remain the same. You will have to change the sensor definition but all the Kavlico sensors will show up on that page already. Those sensor definitions were added with a previous Skyview software update so you simply designate the one you installed. I changed both the fuel and oil pressure. Dynon says the new sensors are both more accurate and last longer. So far, so good.

 

[N74846]

The fuel sender has been changed once already....

 

[Garrett]

Are the sensors engine mounted, if so remote mount on the firewall. Vibration damages them and shortens their life

 

[N74846]

The fuel transducer is mounted on the firewall. I hate to invest in another transducer less than two years from the last replacement.

 

[Garrett]

My fuel sensor is a cheap $15 VDO 0 to 15 PSI sensor firewall mounted working good for over 400 hours. Also try having the opening facing down so that no particles get trapped in the sensor port opening to include periodically flushing the line since it is a dead end.

 

[swatson999]

What kind of transducer? VDO or Kavlico?

 

[Raymo]

Check the EMS sensor page for the reading from the sensor (voltage?). I suspect the sensor is sending an erroneous value, which SV is translating to 3 PSI.

Also confirm the correct sensor is configured in the EMS setup.

Dynon stopped using the older style sensors due to these types of issues. Kavlico is preferred.

 

[N74846]

A Kavlico transducer was installed two years ago and ran fine for some time. I will check the EMS sensor page for any voltage. Thanks for all the suggestions so far!

 

[N74846]

I finally had time to find and check the EMS menu and found the following with only the SV on: (Kavlico 15 psi) raw 1320, cal(v) 1.6113, value 4.065. With engine and elect pump on: raw 2065, cal(v) 2.5208 value 7.486. Configuration range is currently set to: yellow 5.8-7.2, red 7.2-8.0.

Does this mean anything, or help to trouble shoot the problem?

 

[kurtfly]

The numbers you show "Raw" is the raw count 12 bit system = 0 to 4095 counts, Volts is the equivalent voltage @ (0.00122V/count) and the Value is with the calibration coefficients applied (EU's or Engineering Units, PSI).  Based on these numbers it looks like your sensor is bad.  To verify, you can unplug the sensor input wire (green at sensor, brown on SV side if going to pin 8), and ground the brown wire to same point as the sensor black wire.  This will force the SV input to 0 Volts.  If the SV Sensor Debug Data then displays, 0 counts, 0 Volts, and -2.08 PSI the sensor is bad.  If it displays significantly different you should check your grounds.
Good luck,

Kurt

 

[N74846]

Thank you Kurt. This will finally determine if the unit is bad. I assume there is no way to'0' out the error and adjust for the voltage output.

 

[kurtfly]

It is possible to adjust the C0 term in the calibration to shift the offset but I would not recommend this. Unless you have the ability to perform a sensor calibration to check the other terms, this is a 3rd order polynomial you will be getting bad data. Is the sensor output repeatable. Bad data is worse than no data. You might as well just disable the fuel pressure reading and use the fact the engine is running so I must have fuel pressure.

Another way you can check the sensor is to monitor the GREEN sensor output line with a digital volt meter. Connect meter red lead to sensor green wire. Connect your meter black lead to the BLACK sensor wire and with 0 pressure applied to sensor and the SV powered up to provide 5V excitation to sensor, you should see +.54 Vdc on green wire. This is the sensors output with 0 pressure applied. The Sensor RED and BLACK wire must remain connected to aircraft harness. Based on your #9 post your sensor is outputting about 1 volt too high. You can then check your ground to the sensor. A bad ground can increase the sensor output. If a known good ground does not correct, the sensor is bad.

 

[N74846]

Thanks again! You've been very helpful!

Steve

 

[Dynon101]

Does anyone know the part number for the "Legacy" (VDO) fuel pressure sender? I have a fuel injection engine so I need the 100411-001 unit.

I ask because my fuel pressure shows 7 PSI even when the engine is stopped. It is firewall (actually adel clamped to the engine mount) mounted and the electrical wires are on top and the port on the bottom.

 

[Dynon]

The legacy part number is the one you called out - 100411-001.

We have the modern style of sensor for both injected and carbureted engines available though. For fuel injected engines, this is the newer sensor (101692-000) that we've been selling for years:

http://www.dynonstore.com/#!/Fluid-Pressure-Sender-Kavlico-1-8-27-NPT-75-PSI/p/52526487

We no longer sell the legacy 100411-001 sensor, but the Aircraft Spruce part number is 10-01568.

 

[Dynon101]

Thanks for the information.

I was hoping to find one locally and/or cheaper than AS. What is the VDO part number?

 

[Dynon101]

I looked up the Aircraft Spruce part number is 10-01568 that Dynon recommended on the AS site and it states: VDO pressure senders are not to be used with any type of fuel application.

Is there a concern about the membrane getting dissolved/attached by fuel?

 

[Dynon]

Not in our experience. but note that these aren't sensors that we currently actively sell and support. We can't speak for the manufacturer, but it appears that they may have added some new stronger usage guidelines since the time that we sold them. The main reason we moved away from those the mechanical sensors is because the internal moving "wiper" that generates a reading tends to get stuck after a while, which can produce erroneous readings. We think this effect may have been exacerbated by the high vibration environment that is common in piston aircraft. In any case, they would fail (not leak). In any case, even if you're replacing a failed sensor, we'd generally recommend not using this style sensor, and instead using the ones that we currently sell and support.

 

[Dynon101]

Does anyone know the VDO part number of the 0-10 bar sender?