What fuel pressure range should I be seeing for a Lycoming IO-360 in a Lancair 360 (N360DE)?

 

Randy,

 

This may not be relevant.  The Lycoming Manual for a IO 320 states that the fuel pressure can be between 12 and 50 psi.  I would check the appropriate Lyc engine manual.  It has generally been the case that 26-28 psi is maintained for normal operation of my 320.  My measurement is taken from a tee at the exit of the engine driven pump with a fine-hole restrictor in the tee.  There are operational problems when the pressure drops to or below 12 psi and everything is hot as this allows vaporization to occur in the system anywhere after the engine driven pump.  As a matter of fact, sometimes the pressure drops because of vapor induced cavitation of the engine pump.  This is fixed by application of the boost pump.

 

Is it possible that the flow by the tee is artificially reducing the pressure seen by the sensor because your tee is in the flow stream (Bernoulli)? 

 

It is reasonable that the boost pump only adds +2 psi (that's what mine does), thus it is hard to imagine both pumps being bad - i.e. delivering lo pressure.