My probllem with fuel starvation.  The fuel pressure regulator is another component to look at.   A few weeks ago, while in flight, the engine started to loose power.  A quick scan showed the fuel pressure going down, it went down to about 7 psi.  I switched fuel pump B on.  the pressure came up to about 27 psi. with the two pumps on and I landed,  I was in the circuit at the time.  While taxiing back to the hangar I turned pump A off and the pressure went down, then I turned pump B off and the pressure went down.   The next day I went back to test the system, I started the engine on one fuel pump, as usual, the fuel pressure was  about 38 psi. as it has been every time before.  Did a few runs on the runway to warm things up, (no takeoff) everything was ok, fuel pressure was normal all the time, on one fuel pump of the other.   Returned to the hangar, ordered a new fuel pressure regulator (a new MAZDA regulator) and installed it a few days later, went flying.  The problem never returned.