Fuel flow/pressure anomalies on RV7a

Hi

We just purchased our RV7a and I flew it from Florida to London, ON yesterday. As this was a pretty long flight, I got to know the machine a bit. It has a Lycoming TMX - 360 200hp FADEC engine in the machine. I used the checklist power setting of 22? of MP and 2350 RPM and we were around 4500 MSL on the flight. The fuel pump has three settings, On, Off and Auto and the checklist and POH state to leave it on Auto during all stages of flight.

On our first leg, all was well. Fuel flow was 9.1-2 gph, fuel pressure was about 25.

Second leg, after about 30 min we noticed that the fuel pump had come on and stayed on. Fuel pressure and flow were the same as the previous leg, but now the pump was running. When we shut the pump off, the fuel pressure went down to 15 and the fuel flow went up to 10gph. Again, there is no mixture control in this aircraft, so the computer handled that adjustment on the mixture.

My logic was that I did not want to burn the electric pump out if the mechanical pump was operating well enough. We noticed no change in the engine sound nor performance, just the flow went up and the pressure went down.

Is this normal for these aircraft?

Any help or suggestions welcome

Braden Messenger
RV7a - N6716

Very few RVs have FADEC installed (other than the -12), so finding out what is "normal" may be difficult.

If there are a lot of hours on the mechanical pump, it may be time for a replacement. The internal diaphragm eventually goes bad and will leak, causing low fuel pressure. Depending on where your flow transducer is located, the increase may be due to some fuel going out the drain tube of the mechanical pump.

Bubbles going through the FF transducer will increase the readings even if the actual fuel flow is constant.