Fuel pressure variation on FX-3

[andrew.brauer]

This is one of the best written replies I have seen in a blog post. Thank you for taking the time to provide this.

I have one question: Are there any downsides to flying with the electric fuel pump always on? One of my instructors taught me that it is safer, helps to avoid risk of clogs caused by low pressure and that in the end these pumps are so robust that they work for thousands of hours. In the end, the cost of eventually replacing the pump is worth the mitigated risk.

Any thoughts or advice on this?

Once again, thank you for the excellent response and the detail you provided. I learned a lot.

AvW

Appreciate the kind words.

We recommend running the boost pump during takeoff, climb and landing operations as well as for cold-start priming and for the emergency procedures outlined in our E-AB AFM template The boost pump is rated for continuous duty, so technically there is nothing wrong with running it during all operations, though it is still ultimately an electric motor with metal components. Nothing is failure-proof. My main concern would be if the electric pump were to fail during cruise, you would not necessarily have any indication of its failure. Then say by some chance the very robust mechanical pump failed during go-around - you would not know to expect an immediate engine-out, because you didn't know your backup had gone. During ground run-up and approach to landing, you have positive indication of boost pump function in the form of a slight running pressure bump. A loss of that little bump would be very hard to notice in the middle of a long cruise leg.

I'm not suggesting that this is a likely scenario by any means, but you may want to weigh the odds and risks against each other.

[kiwibob]

As for readings from zero to 53psi, I would definitely be looking at the electrical side of things: connections or maybe even the transducer itself. The pump maximums are designed to be under 35 psi at zero flow and the engine fuel injection system requires more than 14 psi to run properly. If the engine is running well, the injector inlet itself is seeing 14 psi or above.

Thanks Andrew,

Finally got my plane in for it's 100 hour and replaced the transducer. Bingo, smooth(ish) fuel pressure. The very high readings (35-36psi) happened when using the electric pump on t/o and during some circuits.Screenshot 2020-05-27 at 14.11.58.jpg

The restrictor and new fuel filter are still stuck in transit due to the Covid19 backlog so I havn't had a chance to fit them yet.

[Daveembry]

Last year I was doing some research on fuel pressures and it was suggested that the electric fuel pump pressure be set close to the same as the mechanical pump. The electric pump is adjustable with a very small Allen head screw and set nut. Turning the screw counter-clockwise lowers the fuel pressure. I’ve always had to adjust it almost completely out to lower it enough to get close to the mechanical pressure (and it still wouldn’t go quite low enough but got very close). Just FYI.

Thanks Andrew,

Finally got my plane in for it's 100 hour and replaced the transducer. Bingo, smooth(ish) fuel pressure. The very high readings (35-36psi) happened when using the electric pump on t/o and during some circuits.Screenshot 2020-05-27 at 14.11.58.jpg

The restrictor and new fuel filter are still stuck in transit due to the Covid19 backlog so I havn't had a chance to fit them yet.