Low fuel pressure indication

[Urs Heim]

I keep getting low fuel pressure indications, occasionally and erratically. I first suspected vapour lock since I do not have the return line installed. But I also got low pressure indications where there was clearly no posssibility of vapour lock. I have heard from CTLS people that the problem might be related to where the sensor is located. On my plane (dual Dynons), the sensor is somewhat lower on the fire wall than the fuel distribution "spider". This way fuel is trapped in the line to the sensor, as it is being held there by gravity, and over time creating residue while being "cooked" over and over by the high temperatures under the cowling, which in turn may clog up the sensor. Suggested solution is to blow out the sensor line regularly and use some carb cleaner on the sensor hole, or install the sensor higher on the firewall.

I have not got around to trying this, but it seems reasonable.

Urs

[David & Jean-Marie Bonnar]

Hello Urs.

1) I would also recommend making sure that the fuel pressure sensor is rotated so that the inlet is facing "up" insuring that any bubbles in the line don't sit against the sensor diaphragm. Air directly against the diaphragm can cause erratic readings. This has helped us.

2) The Dynon resistance-value-to-pressure conversion tables coded into the EMS are not perfect and Dynon has suggested installing a resistor in series with the sensor to raise the indicated pressure if needed to reflect actual fuel pressure. Resistance depends on the amount required for correct pressure indication. See the Dynon site for details. I have not done this.

Best regards,
.dxb

[Urs Heim]

Hi David
Good points.
Blowing out the tube to the sensor has helped. We are doing this at the 50 hour service interval.
A new problem that has surfaced is erratic oil pressure indication. I will change the (old style) sensor, which does not have a good reputation. Also the oil temperature has been acting funny lately: 20 deg C fluctuations at temperatures above 80C. I suspect poor ground contact.

Best regards
Urs

[Urs Heim]

Follow up:
It was indeed a poor ground contact-the bolt had come loose. Also had the oil pressure sensor exchanged for the new type and a another ground lead. installed. Everything works fine now.

Urs