David,
It might be worthwhile to temporarily connect a mechanical gauge to the pressurized section of the fuel system to verify that the fuel pressure sensing system is working correctly.
I have had a similar situation where the fuel pressure was lower after turning on the second HP pump and then the fuel pressure was higher again after turning off one of the pumps. In my case, the problem was caused by an aftermarket adjustable pressure
regulator that had excessive friction in a moving piston seal. The pressures weren't perfectly reproducible and the problem was solved by a change in the design of the fuel pressure regulator with an update kit. I later changed to the stock Mazda
fuel pressure regulator and that has worked fine also.
It may also be useful to look at the effect of disconnecting the vacuum line at idle. For my installation with the stock Mazda regulator, the fuel pressure is close to 42 psi at full throttle or at idle with the vacuum line to the regulator disconnected.
At idle with the vacuum line connected, the fuel pressure is close to 36 psi.
RV6A, 1986 13B NA, RD1A, EC2
From: Rotary motors in aircraft [flyrotary@lancaironline.net] on behalf of hoursaway1@comcast.net [hoursaway1@comcast.net]
Sent: Tuesday, June 12, 2012 5:11 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Fuel presure question.
Question about fuel pressure indications, at fast idle 2200 RPM, fuel pressure is 42 PSI on EM2, if I switch on the back-up pump with the primary pump the pressure drops to 35 PSI, can here both pumps running, if I switch off either pump pressure goes back
to 42 PSI. My system is 13B, stock red injectors all four, pressure regulator is stock Mazda on the end of fuel rail with vacume connection from dynamic chamber. Thanks, David R. Cook RV6A Rotary.