Intermittent high fuel flow indication
in 912 / 914 Technical Questions
13 years ago
Aircraft information: RV-12, 912ULS, DYnon D180, 35 hours TT.
Fuel system configuration: 20 gal tank, electric boost pump, FT-60 flow sensor, gascolator, engine driven pump, pressure sensor and return line to tank.
Over the past month I made several cross-country flights, and tweaked the Dynon K factor as specified in the Dynon manual. Got it to the point where my fuel used (by Dynon) and fuel added (at the pump) were within .1 gallons. Pretty darn good, and was starting to feel confident in the Dynon readings.
Then - on my most recent trip, on climbout from Muskegon, MI, I got a high fuel flow alarm and a reading of over 10 GPH, up from the usual full throttle climb flow of 6.5 GPH. I leveled at cruise and the high reading continued. (I have the Dynon downloaded data file at the time of the incident.)I was clearly not really burning that much gas, as the engine continued to run fine and my actual consumption was normal for the leg. When I pulled the fuse for the electric boost pump, the flow returned to normal. This happened again on the next leg. Sudden onset, electric pump OFF back to normal, electric pump ON back to high rate. On my last leg all was normal.
I have yet to pull the top cowl and check the fuel pump for any signs of trouble - plan to do that tomorrow but would be surprised to see anything obvious. Is it possible the electric fuel pump is overpowering the engine driven pump and forcing extra fuel back through the return line? And why would this be happening intermittently? By any stretch of the imagination could this be a failure mode of the old style pump, and should I plan to replace it?
Any advice/theories appreciated.
Fuel system configuration: 20 gal tank, electric boost pump, FT-60 flow sensor, gascolator, engine driven pump, pressure sensor and return line to tank.
Over the past month I made several cross-country flights, and tweaked the Dynon K factor as specified in the Dynon manual. Got it to the point where my fuel used (by Dynon) and fuel added (at the pump) were within .1 gallons. Pretty darn good, and was starting to feel confident in the Dynon readings.
Then - on my most recent trip, on climbout from Muskegon, MI, I got a high fuel flow alarm and a reading of over 10 GPH, up from the usual full throttle climb flow of 6.5 GPH. I leveled at cruise and the high reading continued. (I have the Dynon downloaded data file at the time of the incident.)I was clearly not really burning that much gas, as the engine continued to run fine and my actual consumption was normal for the leg. When I pulled the fuse for the electric boost pump, the flow returned to normal. This happened again on the next leg. Sudden onset, electric pump OFF back to normal, electric pump ON back to high rate. On my last leg all was normal.
I have yet to pull the top cowl and check the fuel pump for any signs of trouble - plan to do that tomorrow but would be surprised to see anything obvious. Is it possible the electric fuel pump is overpowering the engine driven pump and forcing extra fuel back through the return line? And why would this be happening intermittently? By any stretch of the imagination could this be a failure mode of the old style pump, and should I plan to replace it?
Any advice/theories appreciated.
