Fuel pressure fluctuation at higher altitudes, M20J

[carusoam]

What rate are we able to collect data with the new G EIS?

Looks like 1 second seems to be the new standard…

Not fast enough to pick up all of the pulses generated by the mechanical fuel pump that is driven by a mechanical finger pushing on the diaphragm…

The mechanical pump probably is geared to be a function of rpm…

 

lets see if we can define what normal looks like…

can’t tell from one graph… if this is normal or not…

Heat, and altitude, are known to cause fuel vapor bubbles… TC’d Mooneys have a procedure to use the electric fuel pump when bubbles are a concern…

PP thoughts only, not a mechanic…

Best regards,

-a-

[ArtVandelay]

Me too. I never noticed it with the factory gauges, but did when I installed the G3X with EIS. The engine and plumbing were unchanged, but the transducer is different. I added a snubber which improved it at lower altitudes, but at higher altitudes I can see it still wander. I think it might be heat causing vapor in the lines. The fuel pressure continually increases to an off scale reading after shut down with the mixture in ICO due to heat soaking. 

You wouldn’t happen to have the part number of the snubber you used?

[PT20J]

4 hours ago, ArtVandelay said:

You wouldn’t happen to have the part number of the snubber you used?

Sure, Tom. It was an Omega Engineering PS-8E, 1/8" NPT, 5,000 psi max., for water and light oil.  www.omega.com.

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[carusoam]

I think @Ragsf15e is also familiar with the snubbers…

Old fuzzy memory if I got that wrong…

Best regards,

-a-

[Ragsf15e]

On 4/11/2023 at 2:24 AM, ArtVandelay said:

You wouldn’t happen to have the part number of the snubber you used?

If you add one you’ll also (probably) need two adapters on either side because the fuel line is a flared fitting and the snubber is npt.  Be really careful about properly sealing/tightening those fittings as I gave myself a fuel leak when I did it and it was in a tough place to reach to fix.  The leak didn’t become apparent for several flights.  Much cursing ensued.

[PT20J]

On 4/12/2023 at 7:36 AM, Ragsf15e said:

If you add one you’ll also (probably) need two adapters on either side because the fuel line is a flared fitting and the snubber is npt.  Be really careful about properly sealing/tightening those fittings as I gave myself a fuel leak when I did it and it was in a tough place to reach to fix.  The leak didn’t become apparent for several flights.  Much cursing ensued.

Pipe threads are a pain to get sealed properly. My IA put me on to Armite LP-250 (McMaster-Carr carries it in small tubes but I had to call them because online they only had large cans of it). It's ground up lead in a solvent and it doesn't leak, spall or seize. Arminte also has a non-lead version approved by Boeing but I haven't tried it.

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