5-6 psi Fuel Pressure Fluctuations - 400 hr Lycoming IO-390 EXP119 (RV14)

[mikejonesslc]

Over the last couple months am seeing constant, random fuel pressure fluctuations of 5-6 psi from 28-29 psi to 23-25 psi and back to 28-29 psi (the full cycle within a period of 10-30 seconds (ish). From the engine data (Garmin) it happens during climb, cruise and descent with constant 2500 RPM. No fluctuations on ground with engine off and Aux Boost Pump on (steady 29-30 psi) . Any ideas for troubleshooting - especially how to distinguish between a fuel pump problem and a sensor/loose wire problem?

 

[mikejonesslc]

Over the last couple months am seeing constant, random fuel pressure fluctuations of 5-6 psi from 28-29 psi to 23-25 psi and back to 28-29 psi (the full cycle within a period of 10-30 seconds (ish). From the engine data (Garmin) it happens during climb, cruise and descent with constant 2500 RPM. No fluctuations on ground with engine off and Aux Boost Pump on (steady 29-30 psi) . Any ideas for troubleshooting - especially how to distinguish between a fuel pump problem and a sensor/loose wire problem?

Video attached.

 

[Bell206]

Any ideas for troubleshooting -

Is this something new after any maintenance or other change in the past couple months? New equipment installed, etc.?
Do these fluctuations remain in the normal operation ranges?
Is it a repetitive fluctuation every 10-30 sec until on ground? Or does an RPM change stop the cycle?

 

[mikejonesslc]

Is this something new after any maintenance or other change in the past couple months? New equipment installed, etc.?
Do these fluctuations remain in the normal operation ranges?
Is it a repetitive fluctuation every 10-30 sec until on ground? Or does an RPM change stop the cycle?

No changes or new equipment. Fluctuations are within normal range. Random and ongoing - not correlated to RPM. How does an engine driven pump fail at 400 hours? Or is it something else?

 

[Bell206]

No changes or new equipment.

So to clarify, one day out of the blue it started to fluctuate and nothing was done to the aircraft in the previous 90 days to the start of that event?
Or could it possibly be it was there before but you noticed it on that day?

Random and ongoing - not correlated to RPM.

So no fluctuation on the ground through taxi and run-up and its only evident during climb, cruise and descent?
Define what you mean by "random" during those phases of flight?
Above you also mentioned a cycle of 10-30. Could you be a bit more specific?
Do any other engine readings fluctuate?
Does your amp/volt meter fluctuate?

How does an engine driven pump fail at 400 hours?

It usually doesn't fail in this manner from my experience, but I can't say it doesn't have a problem at this point either.

Or is it something else?

I have some suspicions its something else but need more info at the moment as shown above.

 

[mikejonesslc]

Thanks much for the questions and motivation to go back and look at engine data from previous flights. Reviewed Garmin data logs for flights in Jan2025, Dec2024 and Oct2024. The Dec2024 data showed constant fluctuations between 25psi to 29psi at 2500 RPM (initial climb/cruise) but zero fluctuations at 2300 RPM (rock steady at 28-29 psi at cruise altitude 12,500 and during descent at 2300 RPMs). The Oct2024 data showed a few fluctuations of 4-5 psi at both 2500 and 2300 RPM throughout the flight but mostly steady fuel psi (whereas recent flights show pretty much continuous fluctuations at 2500 RPM). My take is the fluctuations are becoming more frequent but maybe best course is continue to monitor at this time at both 2300/2500 RPM settings since fuel psi - even with fluctuations - is still well within normal limits.

 

[mikejonesslc]

The cycle refers to 10-30 seconds between the normal (higher) psi of 28-29 followed by a reduction down to 24-25psi and then back up to 28-29psi. This is a pretty consistent data point meaning fuel psi pretty quickly rebounds from the low point of 24-25 psi to the higher/normal of 28-29psi.

 

[mikejonesslc]

Other engine indications and amps/volts not fluctuating.