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engine driven fuel pump gone bad?

togaflyer

Well Known Member
I took off this morning to escape a cold Georgia day for the Florida keys.
Start up check.
Warm up check.
Taxi to fuel, check.
Run up, check
Take off all normal and green. Boost pump off 1000 feet, fuel pressure normal.

Out of 5K for 9K, fuel throttle, 2700 RPM, I noticed the fuel pressure drops down to 12.8 PSI and starts floating between that and 13 PSI. Boost pump on, PSI back up to 25 PSI. Level off everything running normal. Shut boost pump off, fuel pressure drops to 18 psi and is varies one or two psi. Switched tanks with same results.

Pump back on, back to the hanger. Before shutting down I did a static run up to fuel power. With boost pump on 25 PSI, when switched off it drops down and varies around 18-20 psi.

Total time 180 hours. I think the pump is failing but its not old so checking to see if I should check other things before pulling it.
 
Mine has done the same thing since day one, although usually a bit higher (more like 7000'): Nose up, full throttle/full RPM, and mixture FULL RICH. Solution is to lean a bit (needs it anyway), and/or go to cruise climb (MP top of green arc/2500 RPM): fuel pressure comes back up above minimum red line.
I have no idea why it does this.
 
I?m guessing you fitted the fuel system per the Van?s plans - specifically the fuel selector valve, the filter, the fuel pump, the red cube flow sensor then through the firewall to the engine driven fuel pump. Is this correct?

Carl
 
I know there has been some issues with the cube being installed before the mechanical fuel pump. My cube is between the Bendix Servo and the spider. I looked over the data log back at the house. All my previous flights fuel pressure were a solid 24-25 psi. Two years of flying no issue at all. It was the same today at start up. The log shows that it slowly began to drop right after shutting the boost pump off and really dropped between 5 to 7K feet. With a ground run the pressure drops from 25 to 18-19 psi when the boost pump is shut off. Hit the boost pump with the engine off and it pressured right up to 25 psi. So the sensor is working properly. Figure I just got a fuel pump that was a lemon.
 
Yes, stock plans. I have the newer (circa 2008) fuel selector valve, mounted a little lower than the original. You thinking some vapor forming? I haven't noticed any temperature dependence.
 
What was your fuel temp? I had a similar issue with ground OAT over 100 and the fuel heat soaked. Problem was worse at high flow during climb and went gradually away after on cruise at above 15 K and much lower temps.

I now leave the fuel pump on until established on cruise when the OAT is above 80 F and fuel is heat soaked.
 
If your fuel pressure gets to 12PSI the engine will stumble quite a lot. Perhaps you have a sender issue.

It is normal to run the boost pump in climb and in hot weather for a bit after TOC, especially if the plane has sat in the sun and the fuel is warmer.

If the engine never missed a beat, and you have not commented on that (unless I missed it) then my first suggestion is the sender is faulting at lower pressures, but reading OK with the boost pump on.
 
Togaflyer
Your comment “So the sensor is working properly.” maybe it’s working properly at one end of the range ? Is it a VDO type or something else like the Kavlico used in the Dynon systems ? If it is the VDO I’d bet it’s at fault :) hopefully it’s that simple & therefore cheap to fix.
 
Your symptoms area also indicative of a slight leak upstream of the fuel pump, usually at the fuel selector or another fitting. Put a wrench on all of them and make sure the fuel selector is tight if it is one of the original brass valves.

Vic
 
Thanks I will go over the entire system. Can a pump have a partial failure, i.e. pressure loss during a full power climb out.
 
Rich,
I have had similar issues in the past. The first time it happened was in level flight. Fuel pressure dropped several times in cruise flight. Turning on the electric pump brought the pressure back up. I replaced the mechanical pump and dissected the old pump. It appeared the diaphragm had a slight tear although no fuel or oil was leaking out of the vent tube. I thought the issue was resolved until it happened on climb out again, but it to the same extent. I started to surmise that it was a vapor issue. My fuel system is exactly to plans EXCEPT I added a 90 degree AN fitting where the fuel line exits the wing root. I decided that the 90 degree I added, plus the 90 degree at the tunnel, could be causing turbulence in the flow. To fix this I bent up two aluminum lines without any 90 fittings, the come together under the seat with an AN female coupling. That was two years ago and I have never seen the issue again. In addition, I am seeing a 1+ psi increase in the mechanical pump pressure.
Whether the pump was bad is in question

Another data point to consider, Ivan K had the exact issue you describe. He replaced the pump and it temporarily went away, but now still happens occasionally. I believe Ivan’s is plumbed per the plans. Geoff Combs has a continuous flexible line from his tank to his Andair fuel selector. He has never seen the problem.

I would not suggest over tightening the fittings. If they are not sealing with the proper torque, they need to be re-flared.

Open up the tunnel, and with a full tank of fuel, wrap every joint with a paper towel and let it set for a couple of days. A blue stain will reveal a leaking joint. Also look at the fuel pump vent tube and see if any fuel or oil is being vented overboard. This would be indicative of a leaking diaphragm

Hope this gives you a few ideas
 
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Can a pump have a partial failure, i.e. pressure loss during a full power climb out.

Yes. The one on my RV-6 did. The symptoms were only evident in a climb with the electric pump off. I think the attitude of the aircraft was the determining factor - if the pump was fighting gravity, it lost pressure. Otherwise, it acted OK.
 
Kyle, I was just looking at your sig line. How close is that 2019 (?) RV-10 to being done now?

All of the flying surfaces and fairings are finished including paint, and I saw the painter last week and told him to expect the fuselage in a month or so. Once he paints that, it'll be final assembly time.

And in other calendar related news, today marks exactly 19 years since the first flight of my RV-6.
 
I took off this morning to escape a cold Georgia day for the Florida keys.
Start up check.
Warm up check.
Taxi to fuel, check.
Run up, check
Take off all normal and green. Boost pump off 1000 feet, fuel pressure normal.

Out of 5K for 9K, fuel throttle, 2700 RPM, I noticed the fuel pressure drops down to 12.8 PSI and starts floating between that and 13 PSI. Boost pump on, PSI back up to 25 PSI. Level off everything running normal. Shut boost pump off, fuel pressure drops to 18 psi and is varies one or two psi. Switched tanks with same results.

Pump back on, back to the hanger. Before shutting down I did a static run up to fuel power. With boost pump on 25 PSI, when switched off it drops down and varies around 18-20 psi.

Total time 180 hours. I think the pump is failing but its not old so checking to see if I should check other things before pulling it.

Please reach out to me if you need a new fuel pump. I took delivery of my Thunderbolt engine and removed the fuel pump because I'm using the EFII32 system. As such I have a Hartzell Engine Tech P/N 200F-5002 Fuel Pump I'd like to sell.
 
First, I wanna say thank you all for your input. It?s so nice that we have a great group of people on this forum who will take the time to help you out. The Cirrus group might sip Champaign with each other, but I would rather have a cold beer with this group any day of the week. I had to go out of town so the plane won?t get attention until I get back on the 15th. I plan to check out the system front to back when I get home. My fuel system is all Teflon lines with the only 90 degree turn at the tunnel from the tank. If the lines looks clean and tight, then it has to be a partial failure of the pump. When I have the problem solved I will report back on the results. One thing with the Garmin set up (and most new glass systems) you can look at the engine info for all the flights. Checking back on flight for months, the fuel pressure was the same 24-26 psi. This last flight was the sudden drop, down to 12.8 psi. I forgot to mention that before shutting down I did a full power engine static run. PSI with boost pump on 26 psi, with it off, 18-19 psi, compared to the normal 24 psi
 
Hello Vic

Please can you expand on ?make sure the fuel selector is tight?

If you have the original brass valve fuel selector, there is a nut on the shaft right underneath the handle. Use a wrench to take it off (after removing the handle). MAKE SURE YOUR TANKS AREN'T FULL.
Then the valve assy will comeout. You will see an O-ring on that shaft that dries out if it is not lubes once in a while (fuel lube works). Then the pump will suck air through the shaft.
Sometimes you will notice a fuel smell in the cockpit with full tanks, but not always. Air will leak where the fuel won't.

Vic
 
I’ve had an issue with the fuel pressure dropping on my rocket for years. Usually this happens only during the run up when I cycle the prop. The fuel pressure will drop to anywhere from 10 to 16 PSI. It always comes back up when I run the boost pump. Sometimes it will remain up when I shut the boost pump off after a few seconds. Sometimes it will drop back down. I’ve also noticed it on the landing roll out a few times when I shut the pump off. Engine has never once faltered. I’ve shut the boost pump off on takeoff after reaching a safe altitude and made full throttle climbs to 6000 feet and the pressure has always stayed up. At this point I have:

Replaced the mechanical pump
Replace the original Andair gascolator with an in-line filter
Replaced the fuel pressure sensor
Replaced all of the fuel lines between the tanks, fuel selector, filter, and mechanical pump

There are no 90 deg fittings except the ones on the inlet side of the Andair fuel selector. The general consensus of everyone I’ve spoken to is that the issue is vapor related and that the system must be sucking air from someplace. But I have either tightened and or replaced every fitting and component except the Andair fuel selector itself.
 
Another data point to consider, Ivan K had the exact issue you describe. He replaced the pump and it temporarily went away, but now still happens occasionally. I believe Ivan?s is plumbed per the plans. Geoff Combs has a continuous flexible line from his tank to his Andair fuel selector. He has never seen the problem.
Bill is correct I did and still do have this problem, I have learned to live with it and mostly been able to eliminate it by running the aux pump to the top of the climb. At first I would turn the pump off at 1-2000ft and that was fine initially at lower altitudes in cooler temperatures in Canada.Then I started flying longer trips at higher altitudes (8-11k typically) during the summer and that is when the drop in fuel pressure began.

At first I too thought it was the engine driven pump was the culprit. A new one was ordered and installed but it made no difference. Then the fuel pressure sender was replaced to no avail. Next was the installation of a cooling shroud on the engine driven pump with a blast tube and that didn't make any difference either. Of course, all the fuel lines were checked for leaks, none found.

After much head scratching and consulting with "the experts" and also reading the posts on this forum I have become convinced that this is a Vapor lock issue is not at all unusual in the RV-10 or in other low wing GA airplanes.

The 4 main contributing factors I have found are (1) During climb out. (2) Hot day time temperatures. (3) warm fuel. (4) Full tanks.

I have now eliminated the problem 100% during climb out by running the aux pump to the top of the climb. Occasionally I will have a momentary drop in fuel pressure right after reaching altitude and turned the aux. pump off but for some reason that only happens when the tanks are full.

In summary: At no time during these drop in fuel pressure events did the engine stumble, at times to as low as 12psi. None of the new replacement parts made any difference. I have lowered my warning from 18 to 16psi. and finally, I have learned to live with it and don't believe it is a problem.
 
The 4 main contributing factors I have found are (1) During climb out. (2) Hot day time temperatures. (3) warm fuel. (4) Full tanks.

Another data point...

I, too, have had similar drop in pressure under certain circumstances - exactly as above.

The most striking was a hot summer day enroute to CO, stopped for fuel in KS (forget the airport offhand), the fuel farm was above ground so the fuel was at ambient temp. Now, I do the same after refueling, and leave the aux pump on until after level off.

I have never had any slight stumble or any issue with the engine, but will get an alert from the EFIS due to fuel pressure drop.

Mine is an older kit, with the Van's fuel valve mounted high in the tunnel right under the top tunnel cover. One of the things on my list is to swap that with the Andair valve at some point...
 
Mine is an older kit, with the Van's fuel valve mounted high in the tunnel right under the top tunnel cover. One of the things on my list is to swap that with the Andair valve at some point...

That probably will not help. I installed my Andair valve low and used an extension, but like others have posted, I too suffered from low fuel pressure readings at higher altitudes. Boost pump on would bring it back up, but it would fall again after a couple minutes after I switched it OFF. I never did find a leak in my fuel delivery system and my fuel lines were insulated in the tunnel and around the exhaust. This issues seems to be fairly common, or at least not isolated, so I am following this thread with great interest. As a data point, my boost pump was also Andair and the mechanical fuel pump was shrouded with a blast tube. I never did a suction leak test though.
 
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I have been doing some armchair repairs (since I won’t be working on the plane until mid March) but between this posting and talking to my engine shop it seems to point toward the pump (figuring the fuel line B nuts are tight and nothing unusual with the Andair valve. The one main factor is that two years of flying in all conditions and everything remained the same. Fuel pressure always 24-25 psi. Suddenly the last flight a drop below 13 psi during a climb and during a later ground run without the boost pump pressure remains under 20 psi. OAT was around 8c. My system has only one 90, at the tunnel, all Teflon branded lines, Andair fuel valve, cooling shroud over the pump, and red cube after the Servo. Just can’t see it being anything else. Anyway, is there any difference between the Lycoming and Tempest fuel pumps.
 
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Fuel pressure drop

Had de same fuel pressure drop with once in a while a 1/100 sec felling of a loss of power but all parameter normal on the data recorder. Just the feeling that you may have hit turbulence.

I look over mecanical fuel pump info and they all say that it rarely fail if they don?t fail intermittently.

I change the electric boost pump with the new AFP to have less fitting. Put the redcube between the servo and spider. Didn?t change much thing ( just a better fuel flow reading and more stable)

I found the problem when i empty my tank, Pressurize my fuel line with compress air I?ve put an adaptor on the fitting just after the tank ( don?t pressurize the tank!) and found a tiny leak at the gascolator. And it all make sense. There was no fuel leak. But it was aspirating air that accumulate under the diaphragm. This leak was on the succion side of the mecanical fuel pump. It become under pressure when you turn on the electrical boost pump and pressure return to normal.

It was really a tiny leak. Almost not perceptible. ( tiny bubble once in a while with water and soap) But fuel pressure is rock solid since. So it really worth to test your line between the boost pump and mecanical fuel pump. I search this problem for 2 years and even my aircraft mecanic was reluctant to pressurized the line. He said that if there was no leak with the boost pump on and mixture off, we would not find any leak.

There is a good video on the tempest website. It is a really good video. The air leak is around 11 min but it worth to watch all of it.

https://www.youtube.com/watch?v=fxT4RAEssnw&feature=share
 
Had de same fuel pressure drop with once in a while a 1/100 sec felling of a loss of power but all parameter normal on the data recorder. Just the feeling that you may have hit turbulence.

I look over mecanical fuel pump info and they all say that it rarely fail if they don?t fail intermittently.

I change the electric boost pump with the new AFP to have less fitting. Put the redcube between the servo and spider. Didn?t change much thing ( just a better fuel flow reading and more stable)

I found the problem when i empty my tank, Pressurize my fuel line with compress air I?ve put an adaptor on the fitting just after the tank ( don?t pressurize the tank!) and found a tiny leak at the gascolator. And it all make sense. There was no fuel leak. But it was aspirating air that accumulate under the diaphragm. This leak was on the succion side of the mecanical fuel pump. It become under pressure when you turn on the electrical boost pump and pressure return to normal.

It was really a tiny leak. Almost not perceptible. ( tiny bubble once in a while with water and soap) But fuel pressure is rock solid since. So it really worth to test your line between the boost pump and mecanical fuel pump. I search this problem for 2 years and even my aircraft mecanic was reluctant to pressurized the line. He said that if there was no leak with the boost pump on and mixture off, we would not find any leak.

There is a good video on the tempest website. It is a really good video. The air leak is around 11 min but it worth to watch all of it.

https://www.youtube.com/watch?v=fxT4RAEssnw&feature=share


Real informative video, it probably would be a good idea to use fuel lube on the pump inlet connector o ring, wonder if that is an area of contention for some?
 
For those of you who think it is normal, I am trying to tell you that it is not normal. There is a small leak in the system somewhere, and the engine pump is sucking air through it when the electric pump is not on.

A shroud on the engine driven pump i spretty much needed ont he 10 as well to help with any potential vapor lock issues.

Please, not trying to insult anyone, but most of you know I've built a couple of RV-10's and work on LOTS of others all year long. When I have seen this problem there was a loose fitting or a bad O-ring on the fuel pump suction side.

Vic
 
Yes I plan to check everything. I watched the Tempest video and it was informative. Just a slight air leak and the pump is impacted. My new plan is to inspect everything first including the o ring on the inlet side of the pump. If I find nothing, then I will go for a replacement. I sure hate gremlins.
 
Yes I plan to check everything. I watched the Tempest video and it was informative. Just a slight air leak and the pump is impacted. My new plan is to inspect everything first including the o ring on the inlet side of the pump. If I find nothing, then I will go for a replacement. I sure hate gremlins.
You will be chasing this for a long time and find nothing, I did. I will respectfully disagree with Vic. If it isn't "normal" it is definitely not "abnormal" many Vans airplanes have battled this issue and so have other manufactures. There is a reason why in some Cessna twins I used to fly the aux pumps were on high in the climb and on low during cruise.
 
Problem solved and my results:

Issue identified:

I have a 2 inch rigid line that connects the fuel filter to the boost pump assembly.
There was blue staining on the thread of the connection on the boost pump side of the fitting.
Checking the tightness with a wrench, I got movement and retighten the B nut.
The blue stain was recent and no residue was built up on either the B nut or the floor.
Ground check and flight test confirmed everything was back to normal. 21 or better PSI on the engine pump at maximum demand.

Cause:

6 months ago I removed and cleaned the fuel filter. When installing it, the B nut tightens clockwise, but creates a counter clockwise rotation on the other end, with the rigid line, this caused the B nut on the boost pump side to slightly loosened. Over the last 6 months of flying the normal vibration must have continued to cause the nut to loosen more, and on the last flight it reached a point where the mechanical pump was able to siphon air into the fuel line.

This B nut had been properly tightened and torque stripped. A nice torque strip line ran from the B nut to the fixed portion of the boost pump assembly. After I had installed the filter and tighten the B nut on the filter side, a quick look at the torque line on the B nut (on the pump side) was undisturbed. When I discovered this nut had loosened and tighten it with the wrench, that torque strip line moved in complete harmony, sliding over the fixed portion like it was Teflon. For some reason it did not adhere. So even though it looked right, it was able to shift without cracking the material. Ironically Vic Syracuse wrote a recent article in EAA magazine where he mentions jam nuts and torque striping. Yep! My new maintenance procedure will include checking and verify every nut, even if the torque strip looks undisturbed.

Final note:
I recently made my donation to this forum. I donate even though I am one of the exempts.
The amount of information that flows on this forum is priceless. Figure this, I would have ordered a new pump, 400 dollars. Then when it did not resolve the issue, more headaches frustration etc. The information that flows on this forum save us all countless dollars and hours of frustration. You are not forced to donate, but it is definitely the honorable thing to do if you constantly tap the resources on it.

Safe journeys
 
Good

Took me 2 years and many change without result until i found my minuscule leak without blue stain. Just air suck when under succion from mecanical pump.

But it worth all the work to fly with peace of mind now.

Thank you for the report.
 
Fuel lube

Real informative video, it probably would be a good idea to use fuel lube on the pump inlet connector o ring, wonder if that is an area of contention for some?
I agree, the tempest video is really great.

I've read to be careful with fuel lube - it's a bit like teflon tape - not really recommended for fuel systems despite the name. Little bits of it can clog an injector.
 
I've read to be careful with fuel lube - it's a bit like teflon tape - not really recommended for fuel systems despite the name. Little bits of it can clog an injector.

Got me to wondering if there is a final fine mesh filter in any of the fi spiders?
 
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