Low fuel pressure

Hi Pete

What is the actual fuel pressure?  if it is still in the green arc dont worry about it.  The RV12 installations I have seen have a small "cube" electric pump that is driven by a plunger controlled by a small plunger, spring and transistor with no points.  This inherently produces a pulse, and a clicking sound from the plunger.   The boost pump is mounted near the tank behind the pilot, the mechanical diaphragm pump is on the engine.  With the boost pump on it is common to see a higher pressure total.  The boost pump pushes fuel up the line but the mechanical on its own has to suck the line and overcome the friction within the line as well.  It is doubtful they would ever be the same reading.  

Just my view.

Cheers

How did you check the pressure? Did you turn off the electric pump and wait for the pressure to stabilize, 15 - 20 seconds, or turn the electric off and see a low pressure then turn it back on? 

Hi Peter,

Walt (above) is describing what I see - pressure drop when Boost turned off but within a few second pressure returns, to only slightly less than with two pumps running.

Due to the pressure drop, I wait until I am in Cruise before turning off the Boost pump.

By testing, (turning off the electric pump), at full power you are putting the most demand on the mechanical pump. If the pressure is 2.5 psi or better the pump is capable of supplying the fuel with pressure under the most severe condition. 

If you are uncomfortable turning off the electric pump in the air do the test on the ground at full throttle. Watch the behavior of the pressure gauge.

The engine will not stop instantly because the pressure is low, The carb bowls hold 15+ seconds of fuel, if any fuel is going in it will be longer than that. Test this on the ground also at full throttle using your fuel shut off.

Another interesting note is when you turn your electric pump back on the pressure will spike 6.5 psi or more until it stabilizes.

From what I’ve read and heard a lot of RV12’s have the same issue, but hasn’t been a serious issue.