I have just installed a new fuel pump on my Tecnam Sierra. The previous fuel pump ran perfectly, but I made the change to be in compliance with the 5 year rubber requirement. My old pump provided a very constant pressure, about .28 bar whether at idle, climb, or cruise. I have a pressure gauge that reads pressure off of the fuel rail.
After installing the new fuel pump, my pressure ranges from .39 bar (idle or taxi), to .30 bar (cruise), to .20-.21 bar (climb). If I turn on the electric booster pump, the pressure increases to 0.30 bar immediately. Although the pressures I am seeing are in range, I am not comfortable with the large fluctuation. It appears to be that the pump does not have adequate capacity to maintain constant pressure at the engine fuel demand increases. I have spoken to Rotax factory representatives at the LSA expo in Sebring, and they told me that they have not had any problems like this if the Rotax fuel rail is used. The Rotax fuel rail returns less fuel than the one that is supplied by Tecnam. If this is true, then the cost of replacing the new pump is much higher in that the new fuel rail is about $400 for all parts. I contacted Tecnam in the US, and they have not experienced this problem after changing a fuel pump.
After reading the many posts on this subject, it appears that I am not the only one to experience this issue. I reduced the length of the vent line to get it out of the slip stream, and it provided some help, but the problem is still there.
I am confident that I have done the installation correctly, and that the pressures that I am seeing are real due to the fact that I have a pressure gauge directly attached to the fuel system that was working the moment before the new fuel pump was installed, and that reads the normal pressure of .30 bar when operated to before starting the engine.
Although my old pump runs perfectly, I would be out of compliance to re-install it. Keeping the new pump puts me in a situation where I experience significant pressure variation in the fuel system which I find disturbing although Rotax says it is normal and acceptable.
Any suggestions would be appreciated.
