912-ULS Fuel Pressure After Start
I have a 2016 RV12 with a Rotax 912-ULS, with the higher pressure auxiliary electric fuel pump. Prior to start, the electric pump pressure was always around 4.5 psi, and after start it would go up to 5.1 to 5.6 psi. After a Condition Inspection last week, now prior to start the fuel pressure was 5.6 psa, and after start, the fuel pressure dropped to 4.5 psi. At this point, I was not sure the mechanical pump was working (did not think to pull the fuse). I went ahead and taxied out, did my runup, then shutdown the engine. Now the electric pump fuel pressure read 4.5 psi. I started the engine, and the fuel pressure went up to between 5.1 and 5.5 psi. Back to the increase of pressure after start.
I have always believed the fuel pressure had to go up which indicated the mechanical pump was good.
What should really happen? Does it matter if the fuel pressure goes up or down? According to Vans, though the person said he was not sure, he said it made sense that it would go down.
I thought the POH said to check that there was an increase, but it does not.
Thoughts????
Bob
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Bob