Engine Fuel Pump Failure

[Walt]

Originally Posted by YellowJacket RV9

If you have any air in the line, that can cause fluctuations. Have you bled the line to the sender recently, or before first start even?

Chris

That's ****, old wives tail.

[YellowJacket RV9]

Originally Posted by Walt

That's ****, old wives tail.

Sure seemed to happen to me, but I am aware that anecdotal evidence is pretty worthless, so I'll take your word for it.

Chris

[David Paule]

Originally Posted by RV7A Flyer

....Bottom line...you replaced a part that you didn't know was bad, with a new part that might not fix the problem, because you don't know what the actual problem is in the first place. To top it off, you've messed with a critical system, thus poking the ghost of Waddington who demonstrated that most failures occur in the hours after significant maintenance....

If I remember right, The Waddington Effect found that the incidence of defects increased after scheduled maintenance, and gradually reduced as those problems were fixed. But then came another regularly scheduled maintenance and the situation repeated. The amount of operational aircraft increased when maintenance that had been performed on time intervals was changed to occur upon condition. While failures indeed occurred after maintenance, nothing from his work said not to do maintenance upon failure, just don't do it arbitrarily. Mr. Conrad Waddington can rest easily.

This situation is quite clearly not a regularly scheduled maintenance-related problem. Instead, it occurred and we didn't know why.

One of the recognized and common methods of determining what is at fault in a complex multi-part system is to remove and replace a single component and see what the effect is. We all learned how to do that in general, when we were taught the very valuable technique of making a hypothesis and devising a test that checks it. If done correctly, that gives us some data. If done especially nicely, it gives us limited data that can only have one conclusion.

In this case this is exactly what Jon did: he first determined that turning on the boost pump eliminated the apparent fault. This tended to suggest that the transducer was probably operating correctly, tending to eliminate that potential failure mode. He replaced the mechanical fuel pump (successfully, thus not creating an example of the Waddington Effect while so doing) and flew again. This time the problem was eliminated. And that was all he needed to do to resolve it.

Bottom line, Walt's right.

Please note that the mechanical pump replacement also eliminated another unknown potential problem, that some issue with the boost pump could be creating fuel pressure issues when the boost pump was off. If it had, replacing the mechanical pump wouldn't have affected the symptoms. But now we know that the boost pump is okay.

It might be interesting to open up the old pump and see what was going on with it, but that's not germane to the repair itself. I'd think that a better thing to do with it is see if the manufacturer would like to have it back to do that themselves. That way they could make improvements if any seem necessary.

Dave

[RV7A Flyer]

Originally Posted by Walt

Just for the record I think you did the right thing, some folks prefer getting a** deep into the theory behind every little problem. Like you said, it was not that big a deal to replace the pump and it was the most likely cause of your problem, good for you, pro-active mantenance IMO.

Maintenance must be done regardless of the "waddington effect", perhaps some folks like to use that as a reason not to do stuff

I respect you, Walt, but I think that's a little unfair. I'm not advocating avoiding proper maintenance and troubleshooting, not at all. I'm only saying that I, personally, would not start replacing parts unless and until I a) had a good working theory of the cause, and b) could analyze or test the theory. How many posts have we seen on here where people had a laundry list of things that they *replaced* which didn't solve the underlying problem?

Replacing the pump is fine, but I would then try determine if it was *actually* failing...perhaps by bench testing, then disassembly, etc. Otherwise, I'd always have that little voice in the back of my head saying "what it that wasn't it?" That's why I'm still watching my (every 6 months or so) FP excursions, in the hopes of identifying a root cause.

Maybe it's the aerospace engineer in me, I dunno, but I *always* want to find the ultimate root cause(s).

To the other poster, yes, Waddington found his effect relative to *scheduled* maintenance, so it's not entirely the same thing, but we do know that fixing something that isn't actually broken does introduce additional risks (improper reassembly, primarily).

On-condition vs. scheduled maintenance is an interesting topic...I've seen scheduled maintenance (mandated by vendors/suppliers) that resulted in some *very* expensive downtimes for some seriously complex, critical equipment because of precisely this effect.

[Walt]

From where i sit there's nothing more important to staying alive than keeping the fan turning and the flight controls working. ANY indication of a problem in either one of those systems demands immediate attention and corrective action.

"Root cause analysis" is great for desk jocks, but in my world keeping the fan spinning is way more important than your wallet. "Shotgun" trouble-shooting perhaps, but we need to get this problem resolved now before things go bad.

And if you decide to disect your old pump thats fine but you likely don't have the equipment to determine if was bad or not, and now the core value of that part is 0.

[clutch22]

FWIW, not long ago, I was chasing these same issues shown in the following link.
http://www.vansairforce.com/communit...d.php?t=154433

It was driving me crazy. I replaced the mech fuel pump, flew for a while, replaced o-rings on the inlet/outlet of the pump, flew for a while, and so on.

Each time I would work on the pump, the first 1-2 hours of flight were perfect. Rock solid pressures. Then around flight hour 2-3, the fluctuations always reappeared back to around a 4 psi slow fluctuation. I quit worrying about it.

All this just to say, I really hope you have your problem fixed, but it may reappear in the next few hours of flight.

[kkmarshall]

Fuel pump erratic behavior or pressure fluctuation does not have to be caused by a failing diaphragm,the check valves in the pump can cause this issue as well.
Also any small bit of debris in a check valve. Just a thought.

Keith

[RV7A Flyer]

Originally Posted by Walt

From where i sit there's nothing more important to staying alive than keeping the fan turning and the flight controls working. ANY indication of a problem in either one of those systems demands immediate attention and corrective action.

"Root cause analysis" is great for desk jocks, but in my world keeping the fan spinning is way more important than your wallet. "Shotgun" trouble-shooting perhaps, but we need to get this problem resolved now before things go bad.

And if you decide to disect your old pump thats fine but you likely don't have the equipment to determine if was bad or not, and now the core value of that part is 0.

I thought we had electric boost pumps specifically for issues like this?

[Climb3zero]

This was posted in another fuel pressure thread. One was posted by another guy that I cut and pasted and the next post was by me. I personally believe this is what happens to my plane, but check everything because yours could be the same, or different. Ed

While I was building my 10 Scott S told me about the breather vent line possibly getting fuel in it when the tanks are full while climbing. I tried my best to install the line as close to the top of the tanks as I could. My fuel pressure will drop way down to 5 psi if I top the tanks completely and stay on a long climb. Of course I'll turn on the pump but I've seen 5 psi before I do. The engine has never stumbled during this phase. If I don't fill the tanks all the way it will not happen. Sometimes it doesn't happen with full tanks, just when I am doing long climbs with topped off tanks?? Just another reference


Just want to go on record that my RV-8 built in 2002 with an 400 hour since new IO-360 also sees these fuel pressure fluctuations. I always top my tanks when I fill up and it seems to be directly related to full fuel tanks in my case. Does not seem to be an issue after they burn down a bit. I hate it and wish it was not there but it is. Turning on fuel pump brings the pressure right back. Engine has never stumbled but I turn on the fuel pump as soon as the alarm goes off. Have seen it less than 7 pounds. Ed

[eddieseve]

Hi Guys

I have been reading this thread with interest as I also have a fuel pressure issue.

My engine is a Lycoming IO-360M1B with 800 hrs since new.

Last weekend while flying home from a trip away my fuel pressure went from its normal 25psi to 45psi and stayed there.

CHTs were all approx 320F and EGTs were approx 1440F, basically the the same as always, fuel flow remained unchanged at 33 liters per hour, oil pressure remained unchanged at 79 psi.

Turning on the electric fuel pump made no difference to the fuel pressure indication.

When I landed I checked the mechanical fuel pump overflow, no oil dribbling out, basically all as normal except for the high fuel pressure indication.

I have a Dynon Skyview with Kavlico fule and oil pressure sensors.

I am suspecting perhaps a bad sensor (but they are meant to be bullet proof) more likely a wiring / connection issue?

I have not yet had a chance to dump the data logs.

I also did not look at the fuel pressure after landing during taxi as I was dealing with a 15 knot cross wind and rotor that got all of my attention so will do that this weekend.

Can anyone share thoughts or ideas on what else to check?

Cheers