Fuel Pressure fluctuations? problems?

Julian,

There is no prohibition in the Rotax IM regarding sintered bronze filters- they are currently in use in both commercial and military aviation applications. Just ensure any filter you choose meets the Rotax IM requirements, and any additional certification requirements that may be applicable to your aircraft.

Jim Isaacs wrote:

Julian,

There is no prohibition in the Rotax IM regarding sintered bronze filters- they are currently in use in both commercial and military aviation applications. Just ensure any filter you choose meets the Rotax IM requirements, and any additional certification requirements that may be applicable to your aircraft.

I use sintered bronze fuel filters on my mowers.

Would not use on my plane, as too hard to assess level of blockage - assuming it is encased in a clear/transparent housing.

I talked with Brandon at Kitfox who suggested cleaning the fuel filter which on inspection looked pretty clean. I cleaned it anyway, then demated/cleaned the fittings and reconnected the fuel lines. No joy. Lockwood Rotax did not have a solution.

UPDATE: I ordered a replacement Garmin 0-15 PSIG Fuel Pressure Sensor but when I removed the suspect Kavlico sensor I observed foreign matter in the orifice of the sensor (see photo). The material appeared to be a soft solid blocking on top of a glutinous ‘goo’. I cleaned the orifice with swabs (photo), flushed it with carburetor cleaner and cleaned the opening where the sensor attaches. I also flushed the fuel line to ensure it was clean, reinstalled the sensor and after checking for leaks, ran the engine. Fuel pressure at idle was a steady 5.3 PSIG rising to 6.0 PSIG that stabilized at 5.8 PSIG at 4,500 RPM. I’ll confirm the suspected problem.

I suspect what I found was a combination of fine particulate that passed thru the fuel filter (dirty gas) and ethanol/water that you see when testing gas for ethanol. I generally fly with 100LL and occasionally with 95 Octane gasoline which contains up to ~8% ethanol but I cannot be sure. 

See pics. I appreciate the help.

Problem solved!

As instructed, I made a big cut in the sealing gasket.
It's surprising that this was effective, given that there appear to be no holes in the housing, see attached image.

Anyway, I climbed to FL100, and the needle stayed nicely in the green!
Before, the fuel pressure indication dropped to almost zero when climbing to 3500 ft.

I've been wondering for years why this was happening and I'm glad that you provided me with a simple solution.
Big thanks James!

Glad your problem is solved, quick and easy, just like my similar problem was solved.

I have a strong hunch that there are many other folks out there who are living with intermittent fuel pressure fluctuations, especially on climbout, who could easily solve this problem. I am surprised that Kavlico, Dynon, Rotax, etc. doesn't publish warnings/bulletins in visible places about this common, easily fixed problem.