Quote Originally Posted by Backpacker View Post
I have a Rotax 912 UL and when i rigged in my fuel pressure dial guage I installed the Rotax return flow orifice(I never had it when i first got my Chinook) and I installed a filter before the orifice to prevent stuff getting to the orifice...been a long time but i i had some low fuel pressure sometimes and remember one time finding something partially blocking the return orifice(I think it was after that i installed a filter before the orifice...the orifice hole is small...so if a chunk of something was sitting near the orifice it may not block flow until full power when it could get swept up and partially block the orifice...something worth checking...but depends where the supply for the pressure reading is from. When i first got my Chinook it never even had a return orifice, only a return line and never had a fuel pressure guage then either but had no issues.
A plugged orifice either at the pressure sender or the fuel return could definitely cause low readings but in my case, that was not the issue. My intermittent low pressure only came at full power on climbouts and never occurred any other time. Were it a plugged orifice, it would have been constantly low pressure or the pressure would have randomly gone low at various phases of flight. As an update, I now have 80 hours on the engine since I replaced the mechanical fuel pump and have not gotten any low pressure warnings.