Question Fuel pressure fluctuations in flight (fuel pump off)

[Neal]

Found it. Attached.

 

[Cactus Charlie]

Has anyone ever found any significant contamination in the Andair filter?

I have never found any and don't see how it is possible if the gascolator is clean.

 

[Neal]

I was wondering that, didn't want to ask. Risk of messing with the fuel system vs. findings in the filter. Probably not something I'm going to do as anything that can make the engine stop is not something I touch so it will be my local A&P to do.

 

[ve6yeq]

Has anyone ever found any significant contamination in the Andair filter?

I have never found any and don't see how it is possible if the gascolator is clean.

From what I have heard, the gascolator screen catches the vast majority of contamination, and if the gascolator is clean during the 100 hr inspection, you can skip checking the Andair filter. However, as the Andair filter is finer than the gascolator, if you find anything in the gascolator, you should also check the Andair filter.

Personally, I have never found anything in the gascolator other than a couple of small drops of water, which I think are from condensation because I do not always refuel to full after every flight.

 

[Cubonaut875]

Interestingly, right before my ignition coil failed, I had a lot of spurious fuel pressure readings, tested pressure all normal. Then the coil failed, replaced the coil and then all the fuel pressure fluctuations normalized. Maybe a coincidence - just throwing it out there.

 

[Neal]

I have exchanged several emails with Brandon Dildine at

Technicalsupportn (Lycoming)<[email protected]>

He has always been helpful and supportive. I do no know what discretion he may have on warranty claims.

The parts in the fuel pump that could fail are the diaphragm, the inlet valve, and the output valve. I doubt any of these would have failed at such a low time. I would expect contamination intermittently preventing sealing of the input valve.

Perhaps Lycoming will take an interest in this early failure and offer an exchange part. Send your data to Lycoming and ask for support.

Well, I emailed this address when you provided it. Nothing heard to date, sadly.

 

[Neal]

Last night's flight, 22/22 and then trying 23/22 and still getting the back and forth oscillation between 25-29. Drop to 20/20 and it appears stable as is at 24/24.

Any opinions? Anyone else care to see what there's does at 22/22? Is this a safety of flight issue or something I can continue to monitor? Never heard back from Lycoming from my March 23rd email inquiry.

Click image for full size.

 

[Cactus Charlie]

The pressure variation shows a distinct difference with changes in rpm. I would be inclined to see if the variation depended on fuel flow.

You could run a bit rich a 2100 and leaner at 2200 so the fuel flows are identical for the two rpm conditions. A similar test could be run with changes in MP to give identical fuel flow at 2100 and 2200 rpm.

If the test results show the pressure variation depends only on rpm, and not on fuel flow or power, then I would suspect a data sampling artifact. The nature of the mechanical pump means that fuel pressure must vary as the pump cycles. How the GEA 24 sees those pressure variations will depend on the relationship between the pressure sampling time and the actual pressure variation.

 

[Neal]

I did go full rich enroute back to the airport at 24/24 and it was stable. I'll experiment with that in the zone where I'm seeing this issue on the next flight.