During the flight from the LAA Rally at Sywell to Bridlington I kept getting the Fuel Pressure alarm (5 psi) and was bouncing around. When the electric boost pump was on the fuel pressure was steady.This happened on the two local flights so to be safe I pulled the strainer (inside a gascolator after the fuel selector and before the electric pump). It had some fluff and hair! but not enough to cause any suction issues.
This happened for a few flights and I discussed with the boys on my shift at the refinery and we came to the conclusion that it was probably due to gas/air in the line from the mech pump to the fuel pressure sender on the firewall.
So we pressured the line with the boost pump and bled the line at the sender manifold and we got rid of some gas bubbles.
This cured the problem and now the pressure just bounces in the green sector as you would expect from a diaphragm pump.
