Somewhere during my trip a few weeks ago, I had noted that the engine seemes to be running a bit rich from where I had set it.  I then noted that the fuel pressure was reading high – like about 48 -49 psi; and I have the regulator set for 40 psi at WOT. Not know what else to try, I switched from pump 1 to pump 2. After a bit the pressure was back to normal; and worked fine after that.

 

My thought later was that switching the pumps should have nothing to do with it.  The two pumps are in parallel, then the filter, then the pressure sensor, then the fuel rail with the regulator on the end, bypassing back to the tank.

 

Last week on a short flight I noted the fuel pressure bar on the EM2 at the max and blinking. The readout was 50 psi. I watched for a short while nothing changed; then switched pumps.  Nothing changed right away, but the pressure slowly returned to normal. Then running pump1, both pumps, or pump 2 didn't make any difference.

 

I discussed with the expert at TWM (the maker of the pressure regulator) and after some discussion, he was completely at a loss as to what could cause the pressure regulator to act in that fashion.  It is a MAP referenced regulator, and the MAP readout was as it should be.

 

I'm baffled.

 

Al