Engine Fuel Pump Failure

[jonweisw]

Adding a data point on this.

I have about 900h on my RV-8 with a Lyc IO360M1B, which was installed new with the airplane. Nine months ago, I upgraded my panel to dual G3x's from, among other things, the Grand Rapids EIS system.

At about the time that I was testing out my new avionics, I noticed occasional fluctuations in fuel pressure, from a baseline of about 24psi to momentary lows as much as 14-15psi. The dips were transient, occurring maybe once or twice per hour, and not associated with any changes in engine output, RPM/MP, or sound/tone. They seemed to happen at higher altitudes during prolonged cruise (6-9000'), but were not associated with temperature. There were no changes in fuel flow. Activating the Aux Fuel Pump remedied the low pressure without hesitation or fail. It is possible that this was occurring with the EIS system and that I missed it.

I decided to have the fuel pump replaced before it failed outright. Upon removal, there was nothing out of the ordinary; no debris, no leaks, no undue chaffing or obvious wear. I did not take the pump apart to inspect the diaphragm.

The new pump is generating 32-34psi consistently, hence confirming (to me at least) that the original pump was in slow failure mode.

I was under the impression that these pumps rarely fail.

Hope this helps someone in the future.

Jon Weiswasser
N898JW, RV-8
IO360M1B

[RV7A Flyer]

Originally Posted by jonweisw

Adding a data point on this.

I have about 900h on my RV-8 with a Lyc IO360M1B, which was installed new with the airplane. Nine months ago, I upgraded my panel to dual G3x's from, among other things, the Grand Rapids EIS system.

At about the time that I was testing out my new avionics, I noticed occasional fluctuations in fuel pressure, from a baseline of about 24psi to momentary lows as much as 14-15psi. The dips were transient, occurring maybe once or twice per hour, and not associated with any changes in engine output, RPM/MP, or sound/tone. They seemed to happen at higher altitudes during prolonged cruise (6-9000'), but were not associated with temperature. There were no changes in fuel flow. Activating the Aux Fuel Pump remedied the low pressure without hesitation or fail. It is possible that this was occurring with the EIS system and that I missed it.

I decided to have the fuel pump replaced before it failed outright. Upon removal, there was nothing out of the ordinary; no debris, no leaks, no undue chaffing or obvious wear. I did not take the pump apart to inspect the diaphragm.

The new pump is generating 32-34psi consistently, hence confirming (to me at least) that the original pump was in slow failure mode.

I was under the impression that these pumps rarely fail.

Hope this helps someone in the future.

Jon Weiswasser
N898JW, RV-8
IO360M1B

Same setup- YIO-360-M1B from Lycoming, now with just under 500 hours on it.

Mine will do this once in a very great while...like every few *months* it will do it, one time. I haven't been able to correlate it with anything whatsoever...not altitude, not RPM, not MAP, not angle of bank, pitch, fuel tank switching, nothing. It drops down to around 14 psi for a second or two (which trips the alarm and wakes me the f**k up in a hurry), then goes right back up to nominal 26-28 psi, and never moves again.

Maddening, but I have no idea what it could be or what to do about it. It's *definitely* in the data, and *not* a single data point glitch (collecting data at 4 Hz).

[Captain_John]

INTERESTING,

I have 722 hours on my Mattituck IO-360 and it has been doing the same thing since it was new three years ago. it usually generates 25 psi but dips to 20 intermittently and has become more frequent as of late.

I am in for conditional inspection now and will be replacing the engine driven pump in the process.

Did you replace with the genuine Lycoming or did you go with Tempest?

Anyone have any comments about brand preference?

CJ

[RV7A Flyer]

I don't think it's a problem with the fuel pump. And I have the Kavlico transducers, so I doubt it's a problem there, although it could be, I guess. I rather suspect a very rare instance of cavitation at some point.

I'd rather not go changing the fuel pump for no reason, not only for the cost but also because I'm rather averse to "fixing" things without knowing if they're broken .

[rv8ch]

If the fuel pump fails, are there any failure modes that would block fuel flow using the aux pump?

[131RB]

Originally Posted by jonweisw

Adding a data point on this.

I have about 900h on my RV-8 with a Lyc IO360M1B, which was installed new with the airplane. Nine months ago, I upgraded my panel to dual G3x's from, among other things, the Grand Rapids EIS system.

At about the time that I was testing out my new avionics, I noticed occasional fluctuations in fuel pressure, from a baseline of about 24psi to momentary lows as much as 14-15psi. The dips were transient, occurring maybe once or twice per hour, and not associated with any changes in engine output, RPM/MP, or sound/tone. They seemed to happen at higher altitudes during prolonged cruise (6-9000'), but were not associated with temperature. There were no changes in fuel flow. Activating the Aux Fuel Pump remedied the low pressure without hesitation or fail. It is possible that this was occurring with the EIS system and that I missed it.

I decided to have the fuel pump replaced before it failed outright. Upon removal, there was nothing out of the ordinary; no debris, no leaks, no undue chaffing or obvious wear. I did not take the pump apart to inspect the diaphragm.

The new pump is generating 32-34psi consistently, hence confirming (to me at least) that the original pump was in slow failure mode.

I was under the impression that these pumps rarely fail.

Hope this helps someone in the future.

Jon Weiswasser
N898JW, RV-8
IO360M1B

I cant say for sure what happens when the fuel pressure drops bellow 14 psi on a 4cyl but I know when it drops below that on my 6 the engine is stumbling. Its unlikely your new pump is putting out 32 to 34 psi. I would suspect the transducer. Fuel pump failures happen but are rare.
Ryan

[RV7A Flyer]

Has anyone with this problem, who replaced the pump, actually dissected it to see *for sure* if it was failing?

It's hard for me to understand how it could fail so intermittently in such a fashion...I'd think once the diaphragm started to fail (or whatever it is) that you'd see pressure drop *and stay there*.

[Kyle Boatright]

Originally Posted by RV7A Flyer

Has anyone with this problem, who replaced the pump, actually dissected it to see *for sure* if it was failing?

It's hard for me to understand how it could fail so intermittently in such a fashion...I'd think once the diaphragm started to fail (or whatever it is) that you'd see pressure drop *and stay there*.

I did not dissect mine, but when it failed, it was an intermittent failure. The only time I had a low FP warning was in a nose up attitude at altitude. Pitch down by increasing speed and it resolved, slow down and pitch up, and it came back with no altitude change.

[jonweisw]

The reason I know it was a failure of the pump and NOT the transducer is that when the dips would occur they could be easily remedied by activating the electronic auxiliary fuel pump. The pressure would return to around 28 psi.

While I may not actually be getting 32-34psi from the new pump because the transducer hasn't been calibrated, it is worth noting that it is 10psi higher than it was reading nominally on the older pump (22psi) and there are no dips.

So, while it may not have truly hit 14psi in the dips (because the transducer wasnt calibrated), the mere fact that it was running half the pressure of what the aux pump could produce and that it was a departure by 40% of baseline was enough for me to change it out. Not worth waiting until complete failure IMO.

[jonweisw]

There is another thread now that is exploring the transducer possibility as an explanation that should be very interesting. In the meantime, here's a screenshot of a typical excursion (G3x data dump to saavy analysis)..