Chieftain engine driven fuel pump problems

marktheone · Post by **marktheone** » Sun Mar 25, 2007 8:42 am

Hi,

I have a Lyc 540, right side, that keeps eating engine driven fuel pumps. We are on the third one now. We have changed and inspected the drive. We have had the U/S ones pulled apart and it doesn't look like anything has gone thru them. This engine has always run well and now has about 2K hours on it. The last 2 pumps have lasted 0.4 hours.

If anyone has any insight on this it would be greatly appreciated.

Thanks,

Mark

Fully Articulated · Post by **Fully Articulated** » Sun Mar 25, 2007 9:33 am

What's the snag on the U/S pumps? Low FP?

marktheone · Post by **marktheone** » Sun Mar 25, 2007 9:42 am

They just flat out quit. When they quit and you only have the low pressure boost pump on the engine would actually quit if you don't put the emergency pump on.

All pumps seem to just work normally and then quit. I have grounded the aircraft until we can sort it out. It is not only financially annoying but could become a safety issue if the electric emergency pump were to quit as well.

We boroscoped the accessory section thinking that maybe a cog was ripped off the gear and that was causing erratic speed changes. No dice, everything looks good. It's confusing as hell.

Mark

Fully Articulated · Post by **Fully Articulated** » Sun Mar 25, 2007 10:04 am

I am sure you have explored this option and I may be speaking out of turn in that I am not familure with your aircraft type. My question is are you sure you have a genuine pump failure and not a indication problem?

Does your FP suddenly go to zero, or do you have a low FP caution light. Is it possible to duplicate on the ground with a wet gauge attached to see what the FP is?

Sorry if I am off-track but I have seen many troubleshooting exercises conducted at great expence when indication was the problem.

Cheers

marktheone · Post by **marktheone** » Sun Mar 25, 2007 10:36 am

Nope not off base at all. When the pump quits the gauge drops and the engine will quit if you don't hit the e pump. On the first replacement pump the shaft was actually sheared off. We thought that maybe the drive was not turning completely true and that was the cause. There is a little bit of design play in the pump to accomadate just that. Changing the drive made no difference. It it turns out that I have to buy an engine I at least want to learn something from this.

We're out of options.

Thanks,

Mark

Fully Articulated · Post by **Fully Articulated** » Sun Mar 25, 2007 10:51 am

I imagine your Fuel pump is a constant displacement pump with excess Fuel flow returning to the inlet side of the pump. A sheared shaft may be due to some type of Hydraulic lock or restriction. I have had a HYD pump shaft shear due to a restriction on the return side.

FA

marktheone · Post by **marktheone** » Sun Mar 25, 2007 12:14 pm

I'm not an engineer but I think that the pump is on a demand basis. Faster the engine goes more pump speed. I will check with the engineers but the return line is very small.

I'm hoping that maybe it is a bad batch of pumps.

Cheers,

Mark

Wrench · Post by **Wrench** » Sun Mar 25, 2007 2:52 pm

not familiar with your type of aircraft. But i am assuming your airframe filters are clean and your airframe boost pump(s) are running fine. If not your edfp wont last long.

marktheone · Post by **marktheone** » Sun Mar 25, 2007 5:27 pm

Yep filters are all clean. Boost pumps are operating normally.

I'm thinking that we'll try putting yet another pump on tommorow and see what it does.

I'll let you know.

Mark

Bullet Remington · Post by **Bullet Remington** » Sun Mar 25, 2007 9:18 pm

The Fuel pumps on the 540 Lycomings are direct drive. That is to sya, they'll turn at whatever speed the accessory drive case is turning.

You've stated that you've gone through 2 pumps with approximately 20 minutes in service on each one? Something rotten in Denmark! I don't believe it is the accory drive itself. It appears to me that something is binding up the pump and the drive is shearing the pump drive shaft/spline.

There should be a gasket between the pump face and the accessory drive case. Is it possible that this gasket is being installed incorrectly and is blocking off the return port? Might be a good tim to have a long look at the maint manual and/or pull back the other pump and have alook.

Another thing to look at is the pump pressure when it is replaced. Is the press in the green or on the high side?

I recently had to remove a fuel pump from a 340 because after O/H the engine fuel pressure was low. In fact the engine would NOT start without the boost pump on, nor would it run without the boost pump on. The end result is that there are two adjustments on the pump. One for high pressure side and one for the low pressure side.

Somebody(( actually several different folks) was adjusting the wrong adjustment bolt?screw and drove the pump into pre-mature failure.

Personally, with the pumps failing in approximately 20 minutes, fersh outa the box, I'd be inclined to have a good look at the blockage possibility, AND failing that, an extra look look at where I'm getting the pumps from!

I would be most curious to learn just waht fixed this problem, in the evnt you get it fixed!

Good Luck!

BR

Bullet Remington · Post by **Bullet Remington** » Sun Mar 25, 2007 9:21 pm

The Fuel pumps on the 540 Lycomings are direct drive. That is to say, they'll turn at whatever speed the accessory drive case is turning.

You've stated that you've gone through 2 pumps with approximately 20 minutes in service on each one? Something rotten in Denmark! I don't believe it is the accessory drive itself. It appears to me that something is binding up the pump and the drive is shearing the pump drive shaft/spline.

There should be a gasket between the pump face and the accessory drive case. Is it possible that this gasket is being installed incorrectly and is blocking off the return port? Might be a good tim to have a long look at the maint manual and/or pull back the other pump and have a look.

Another thing to look at is the pump pressure when it is replaced. Is the press in the green or on the high side?

I recently had to remove a fuel pump from a 340 because after O/H the engine fuel pressure was low. In fact the engine would NOT start without the boost pump on, nor would it run without the boost pump on. The end result is that there are two adjustments on the pump. One for high pressure side and one for the low pressure side.

Somebody(actually several different folks) was adjusting the wrong adjustment bolt/screw and drove the pump into pre-mature failure.

Personally, with the pumps failing in approximately 20 minutes, fresh outa the box, I'd be inclined to have a good look at the blockage possibility, AND failing that, an extra hard look look at where I'm getting the pumps from!

Might be a good time to submitt a SDR and while you're there, have alook around to see if this problem has been reported before. Might find some commonality with what you're experiencing.

I would be most curious to learn just what fixed this problem, in the event you get it fixed!

Good Luck!

BR

Spinner · Post by **Spinner** » Mon Mar 26, 2007 5:28 am

Two complete failures in less than two hours. I would check with the person who is overhauling your pumps. That seems like a high rate to me. We have had fluctuating pressures but never all out failures. Usually the shops can give you a suggestion after teardown.

When installing that pump it is possible to damage the insides if a pressure or side load is put on the drive shaft during install. I have had that happen to me before. Those pumps are also dry spline. There is supposed to be an adapter between the case and the pump.

Keep us posted with updates.

midnight elf · Post by **midnight elf** » Mon Mar 26, 2007 11:42 am

Had a similar failure with boost pumps a few years ago. The engine was overhauled and the tech replaced the accessory gearbox bearings with old "but still servicable" bearings. After about 600-800 hours after OH, these bearings set up a resonance frequency harmonic with the pump. Causing them to self destruct anywhere from a few minutes to 5 hours run time. Espescially at cruise, ground runs would be fine.
Also check the history of the pumps, were they OH'd at the same shop? I have had several items fail because the same OH tech was making the same mistake each time. Perhaps try a pump from a different source. In the mean time ensure the rest of engine fuel system operates normally.

marktheone · Post by **marktheone** » Wed Mar 28, 2007 6:08 am

Ended up having to put a new engine on it. Started making metal in the finger screen after putting another pump on.

I'll post the findings here when I get the strip report.

Mark

Fully Articulated · Post by **Fully Articulated** » Wed Mar 28, 2007 1:49 pm

Sorry to hear that, wish I could have helped.

Make sure you monitor that teardown closely, you may have a warrenty issue if it turns out the resistance from the failing pump damaged your engine. But as usual, it will be hard to prove what came first the chicken or the egg!!!

Good luck,
FA