Fuel Pressure Issues (Low)

Russ, 

As you advance the throttle with the engine running (and manifold pressure increases) does the fuel pressure also appear to increase?  If so it’s a problem with the setup of the fuel pressure sender in the Dynon unit.  Your Kavlico fuel pressure sender is looking at ambient air pressure, but the Rotax fuel pressure regulator is reacting to airbox pressure. The fuel pressure must be controlled in relation to manifold pressure because the injectors are operating in that environment.  

With the engine off, airbox pressure = ambient pressure so the gauge reads accurately. With the engine running at idle, manifold (airbox) pressure is low, which causes the fuel regulator to reduce the fuel pressure accordingly. However, your fuel pressure sender is still reading pressure relative to ambient air pressure so you get a lower gauge reading than the injectors are actually seeing.  As manifold pressure increases and moves closer to ambient, the difference between airbox pressure and ambient pressure is much smaller, thus the sender reads closer to the correct value.  

38 psi at idle (with one pump running) is what I would expect to see if the Dynon is not set up properly to compensate for the difference in ambient and airbox pressure.  I’m not familiar with the Dynon equipment, but your manual should tell you how to set up your display so that it shows fuel pressure in reference to manifold pressure using either of your Kavlico senders.  I would bet that your Dynon settings got changed when the pressure sender was changed, then did not get properly setup again when the old sensor was put back in.  

I know you said you put the old 50 psi sensor back in and still have bad readings, but what you described is exactly what I experienced when I replaced my 50 psi sensor with the new 150 - but no other changes.  My 912iS is in an RV-12iS with Dynon.  I neglected to reconfigure the new pressure sensor for the 150 psi DIFFERENTIAL sensor.  I know it may be a PIA to get to it and change it to the 150 psi sensor again, but I’d suggest doing so and reconfiguring the Dynon for the correct sensor.

And as a side note, not sure of the revision of your sensor database, but back when I replaced mine, the 150 psi differential sensor wasn’t in the sensor file.  Dynon sent me a new file, so, if it doesn’t appear in your list, download the latest sensor file from Dynon’s web site.

Anyway, that was my experience. 

Bob Yanniello wrote:

I know you said you put the old 50 psi sensor back in and still have bad readings, but what you described is exactly what I experienced when I replaced my 50 psi sensor with the new 150 - but no other changes.  My 912iS is in an RV-12iS with Dynon.  I neglected to reconfigure the new pressure sensor for the 150 psi DIFFERENTIAL sensor.  I know it may be a PIA to get to it and change it to the 150 psi sensor again, but I’d suggest doing so and reconfiguring the Dynon for the correct sensor.

And as a side note, not sure of the revision of your sensor database, but back when I replaced mine, the 150 psi differential sensor wasn’t in the sensor file.  Dynon sent me a new file, so, if it doesn’t appear in your list, download the latest sensor file from Dynon’s web site.

Anyway, that was my experience. 

Bob - thankyou for your reply, I've been trying to get Dynon technical support to talk to me (via emial) for well over a week now but they don't seem to be forthcoming with help yet which is unusual as they've always been helpful in the past. However I have the latest updates on the Skyview and the sensor part number selected via the Dynon setup for the new sensor matches the part number installed so I'd hope it's set up correctly. I will try again with the new sensor and look even more carefully at the options available. 

Russ, maybe you have already read this, but if not maybe it could be helpful (from page 7-31 of the Skyview Installation manual) :

The new Kavlico 150 PSI sensor (P/N 103757-000) and the legacy Kavlico 0-50 PSI fuel pressure sensor (P/N 101716-000) are the ONLY sensors that can be used to monitor fuel pressure when SkyView is used to monitor a 912 iS engine. If you use the EMS Engine Setup for the 912 iS that is available from the link above, the selection and setup is already correctly performed for you. If not, the following is required:

If using the new 150 PSI Kavlico sensor, the “KAV V2 150PSI DIFF103757- 000/503851-000” sensor must be selected for fuel pressure sensor selection under SETUP MENU > EMS SETUP > SENSOR INPUT MAPPING.

If using the legacy 0-50 PSI Kavlico sensor, the “KAV 50 PSI DIFFERENTIAL (101716-000)” sensor must be selected for fuel pressure sensor selection under SETUP MENU > EMS SETUP > SENSOR INPUT MAPPING.

Fuel pressure on the 912 iS is measured with respect to the air box pressure. To be able to display correct fuel pressure, SkyView must receive the following data: • Manifold pressure (via CAN bus from Rotax 912 iS ECU), and • Barometric pressure (via SkyView Network from SkyView SV-ADAHRS-200/201)

Jeff Blakeslee wrote:

Russ, maybe you have already read this, but if not maybe it could be helpful (from page 7-31 of the Skyview Installation manual) :

The new Kavlico 150 PSI sensor (P/N 103757-000) and the legacy Kavlico 0-50 PSI fuel pressure sensor (P/N 101716-000) are the ONLY sensors that can be used to monitor fuel pressure when SkyView is used to monitor a 912 iS engine. If you use the EMS Engine Setup for the 912 iS that is available from the link above, the selection and setup is already correctly performed for you. If not, the following is required:

If using the new 150 PSI Kavlico sensor, the “KAV V2 150PSI DIFF103757- 000/503851-000” sensor must be selected for fuel pressure sensor selection under SETUP MENU > EMS SETUP > SENSOR INPUT MAPPING.

If using the legacy 0-50 PSI Kavlico sensor, the “KAV 50 PSI DIFFERENTIAL (101716-000)” sensor must be selected for fuel pressure sensor selection under SETUP MENU > EMS SETUP > SENSOR INPUT MAPPING.

Fuel pressure on the 912 iS is measured with respect to the air box pressure. To be able to display correct fuel pressure, SkyView must receive the following data: • Manifold pressure (via CAN bus from Rotax 912 iS ECU), and • Barometric pressure (via SkyView Network from SkyView SV-ADAHRS-200/201)

Thanks for that Jeff - I can confirm that those are the two sensors I have and that that is the sensor(s) that is set in the skyview and also that the manifold pressure is reading and registered by skyview as is the Baro. It's really annoying as it's only a couple of psi low! Going to check coarse fuel filter and clean manifold pressure regulator tomorrow to see if that helps.