Fuel servo and flow divider troubles

[Bartman]

After installation of my engine she ran great on ground run for about 3 minutes, but one of the fuel hoses to the gauge on the right firewall was leaking so we replaced all of them. Should have done it in the first place but they looked good and all but one was fairly new anyway. After replacing all fuel hoses the run up was very rough and #4 was basically cold. All 4 injectors were cleaned before engine installation, but after installation of new hoses all 4 of them had crud in them. Cleaning twice didn’t solve the problem so I did the flow test. 

This is what I got with flow test and I repeated it several times both with and without injectors and also did throttle at idle and full throttle and got the same relative distributions, except that it changed to just a trickle on #4 the last time I did it. We removed the flow divider and sent it back to the specialty shop. The same shop flow tested a couple of months ago and said the servo was dead on specs and all ADs complied with so I chose not to rebuild it. 

[carusoam]

Great pics Bartman!

what’s next?

Best regards,

-a-

[Bartman]

My question is should I send the fuel servo back? I ran the Dukes electric boost pump for 4 minutes and collected about 1 quart of fuel, but I didn’t want to abuse it any longer. Both finger screens at the Dukes pump and at the Servo inlet are clean I got excellent flow from the hose going from the mechanical pump with it disconnected. About a gallon in only a few seconds with main hose disconnected from the fuel servo. With the flow divider removed I rigged up a hose and checked fuel flow to the divider. This is full throttle, mixture rich, and boost pump on. 
 

[carusoam]

How many hours on the divider so far?

They aren’t indestructible...

And have caused a few problems around here...

Lets see if we can find out a Reliable number of hours before getting It OH’d...

Or see if they get OH’d when the engine does...

 

Best regards,
 

-a-

[Bartman]

The divider and servo were sent off during engine rebuild. We rebuilt in the field and I’m confident about the engine rebuild itself. My maintainer has an excellent reputation for engine work and has a shop devoted just for that for high-performance engines. Anyway, the fuel divider and servo were sent off a couple of months ago and it ran great last week then we discovered the hose leak and replaced all of them. I figure there’s some contamination, probably from the old hose showering debris, But new hoses possibility as well.

[EricJ]

The servo won't cause unequal distribution like you're seeing, since there's only one hose/line from the servo to the flow divider.   Either the divider got clogged up by debris from the old/new hoses and the change process, or the injector nozzles did.

Also, the servo won't make max output pressure unless there's sufficient airflow through the servo/throttle body.   There are ram air tubes and a diaphragm that prevent excessive fuel output if there is no airflow.

 

[Yetti]

The guy in Texas flow tests the divider and servo together.   Pull the servo finger screen and check

 

[PT20J]

The servo just meters total fuel flow according to air flow and mixture control setting. There is one hose that goes from the servo to the flow divider. The flow divider serves two functions: 1) divide flow evenly to the nozzles, and 2) it contains a valve that closes off fuel to all nozzles to insure a smooth shutdown. If the fuel flow is not the same to all cylinders, the problem has to be either something clogging the internal passages in the divider, clogged or unequal diameter lines to the nozzles, or the nozzles. Unlike the servo, the flow divider can be disassembled in the field for inspection and cleaning. The nozzles contain a restrictor and these are matched sets with the nozzle body and care must be exercised when cleaning to not interchange restrictors between nozzles. Also, don't poke anything in the nozzle bores to clean them as this may affect calibration -- just soak them in Hoppes No. 9. You can tell a lot about the nozzle condition by comparing the spray patterns in addition the the baby bottle test. Don't worry about wearing out the boost pump; as long as it is pumping fuel it can run continuously.

See Precision Airmotive RSA manuals attached...

Skip

15-338E.pdf

15-812_B.pdf

[Bartman]

Two more data points. 

I know cleaning these two screens dis not fix or cause my issue, but for anyone who reads this thread in the future make sure you clean the two metal mesh fuel finger screens. The first picture is debris from the screen immediately downstream of my Dukes electric fuel pump and it filters from outside to inside thru the metal mesh. After reading and researching Mooneyspace I understand that one is only found on some E, F, and J models and was installed later by AD due to failure mode of the Dukes pump. The second picture is debris inside the servo screen at the main hose from the mechanical pump where it connects to the inlet at the fuel servo with the screen behind that fitting. That screen filters from inside out and looks pristine when you first take it out, but the surprise on the inside requires a lot of banging on the table and agitation in a bucket of 100LL.

Both screens had similar material and only a trivial amount is picked up by a magnet. I figure it’s debris from the tank sealant,  hoses, and even plant material pollen and stuff like that and even a few animal hairs and bits of feathers from opening the fuel caps. Also looks  like bits of rag and fibers that may be from wiping the fuel nozzle that gets snagged and the comes off when you fill the tank. We are all careful opening the fuel caps, but debris enters the tank every time we open it. 

Edited July 5, 2020 by Bartman

[N201MKTurbo]

I’ve found the best way to inspect the finger screen is to hold it up to the sun and rotate and twist it. You can use a flashlight, but the sun works better. I clean them with compressed air.

But then our sun works all the time. Not true everywhere.

[adverseyaw]

Looks familiar. I had similar symptoms (clogging injectors) and found a similar amount of debris in the strainers. The bits that were causing the most trouble seemed like small sand particles -- very hard, but not metallic.

My approach was to: 1) remove the debris from the tanks, and then 2) clean every component that may have debris stuck in it. In the end, that amounted to:

1. Thoroughly clean the filters and screens
2. Disassemble and clean all of the injectors
3. Open the panels on the tanks and clean them out with terry cloths. This is what stopped the debris from entering the fuel system
4. Overhaul the flow divider and fuel servo as a precaution. My overhauler said they found particles and rust traces, so was glad they were cleaned up.
5. I burned out my fuel pump in the process so had to upgrade that

It ended up being about $6k in overhauls and labor, probably closer to $4.5k without the pump. Sorry to hear you're going through the same. Hopefully it will be less involved for you, but the knowledge that I got everything out of the fuel system is invaluable.

 

[Bartman]

Yaw,

Over the past couple of weeks I read your thread several times, and a couple of others on the same topic. I found your info and that of the thread started by @Yetti from a 2015 thread very valuable. The comments and help from MS posters are very powerful and point me in the right direction every time. I don’t have a lot of first-hand knowledge, but I usually follow up with a thread on my experiences with a  recap and it sometimes ties a couple of threads together like this one.

I’ll post my final result and experiences of my engine removal, rebuild and installation when we wrap it up. 

[Bartman]

Flow divider was serviced and found bits of hose contamination. This is the flow test after service and install. She runs great now, no leaks, prop cycles, and Both CHT and EGT temps look good on two short run ups. One final inspection in the morning and she goes for maiden flight when it’s cool and smooth. 

[carusoam]

Much better! 
 

Great pics, thanks for loading  them up....

Anything special to watch for on the first departure?

Best regards,

-a-

[Herlihy Brother]

Glad you found your problem. I had a similar problem that was difficult to solve...ended up being the same issue...dissolved bits of black hose clogging things in inaccessible places.....now periodic black hose replacement is on my preventative maintenance list.

[Bartman]

On 7/16/2020 at 12:02 AM, carusoam said:

Much better! 
 

Great pics, thanks for loading  them up....

Anything special to watch for on the first departure?

Best regards,

-a-

Everything is special and must be monitored on the first flight 

Seriously though the first flight went well and using NASA terminology all parameters were nominal. I’ll start a new thread and describe my experiences soon. 

[Cluso01]

Currently having a very similar problem on our '78 M20J Hopefully, the fix is in progress.  This thread has been very enlightening.  Thanks to all.

[carusoam]

Welcome aboard Cluso.

Congrats on your first post!

Best regards,

-a-

[A64Pilot]

As breaking down fuel hoses clogged the fuel divider, you may want to consider replacing them.

I’m going out on a limb here, and state that I believe that PTFE (Teflon) hoses last a very long time, much longer than rubber hoses.

If that’s a incorrect statement,  I expect it will be corrected

Edited May 1, 2021 by A64Pilot

[PT20J]

9 hours ago, A64Pilot said:

As breaking down fuel hoses clogged the fuel divider, you may want to consider replacing them.

I’m going out on a limb here, and state that I believe that PTFE (Teflon) hoses last a very long time, much longer than rubber hoses.

If that’s a incorrect statement,  I expect it will be corrected

No, you are correct. From the M20J Service Manual: