rjcthree
Well Known Member
I’m constructing a plan to diagnose a change in fuel pressure behavior in my most recent flight. Previous flights have had stable and predictable fuel pressures depending on the phase of flight (MAP/throttle), with the most recent flight showing wide and rapid variation (needle continuously jumping +/- 2 psi around the mean, mean pressure being also down from typical by 0.5psi with or without the boost pump on) of fuel pressure seen on/by the EFIS. I will add a mech gauge , put a scope on the sensor output, you name it. it’s a D180 with a three wire kavlico 0-15 psi sensor that’s been on the plane for 80 hours. Note no engine running abnormalities were seen in flight or in the data.
After studying the data and doing modest inspection and diagnostics ( not able to run the engine due to rain) I do not have any reason to doubt the data. Boost pump on or off in flight changed the mean by 0.5 psi when on as normal, but did not change the sensed pressure fluctuations recorded and seen. Pressure is steady on the boost pump only when not running.
Even though it’s an Ellison, it’s a typical system, with tanks to selector to boost pump to collator to engine driven pump to carb, which is a pass through to the sensor and primer solenoid.
The question: is it possible the outlet check valve of the engine driven fuel pump, if leaking, could cause the pump to ‘breathe’ from the output side, thereby causing variation?
After studying the data and doing modest inspection and diagnostics ( not able to run the engine due to rain) I do not have any reason to doubt the data. Boost pump on or off in flight changed the mean by 0.5 psi when on as normal, but did not change the sensed pressure fluctuations recorded and seen. Pressure is steady on the boost pump only when not running.
Even though it’s an Ellison, it’s a typical system, with tanks to selector to boost pump to collator to engine driven pump to carb, which is a pass through to the sensor and primer solenoid.
The question: is it possible the outlet check valve of the engine driven fuel pump, if leaking, could cause the pump to ‘breathe’ from the output side, thereby causing variation?