fuel pressure with new fuel pump

[mike morrow]

any ideas to get steady fuel pressure readings

[Jeff Linger]

Mike, did you ever figure this out??

[mike morrow]

i was told by patrick at ussportaircraft to shorten the fuel vent line about 12 inches from firewall out of the slipstream. also, been told there is a modification fuel delivery system to install to solve this issue. unsure of cost and time and have not heard back from leading edge airfoil about parts for this. fuel pressure goes down to 2.0 once every nine hours for a few moments, i turn electric fuel pump on and shows 2.2 or so. engine runs fine at full rpm. i reduce rpm to 4000 and fuel pressure goes up to 3.0 and then goes back to 3.4 or so later. with electric fuel pump as backup unsure if its necessary to do all this modification. frustrating that a new fuel pump causes problems and rotax makes us pay and figure it out.

[Dave Bonnar]

1) Insure Dynon D120 software is current.  Older versions allowed oil and fuel pressure to wander.

2) Insure Fuel Pressure Sensor is angled "up" to the hose to insure that no air bubble can get up to the diaphragm.  For my 2009 SC, I rotated the Sensor counterclockwise about 15 degrees and made a 1" standoff from the host bracket to hold the hose and sensor in that 'up' position. This insures that no bubble will find it's way to the sensor and cause abnormal readings.

3) Fuel rate of flow can cause actual pressure to be inverse of flow rate.  IOW - you go fast, flow goes up and pressure lowers a bit.  Pump catches up and pressure comes back a bit.  You turn final and drop the nose and cut the throttle, flow rate drops as you idle back and the fuel pressure can climb suddenly.  Pressure bleeds away and fuel pressure indication changes.  

So - keep fuel flow and residual pressure in mind as you try to sort the problem out.

Cheers - 

[mike morrow]

thanks for this information and it makes sense that fuel pressure increases when i reduce throttle. will tell my A & P at annual about angling up the fuel pressure sensor. thanks