Crud in my fuel servo strainer

[adverseyaw]

I'm stumped and could use a hand with my IO-360 in my 1978 M20J.

I'm collecting small particles in my fuel servo strainer. Occasionally some sneaks through and clogs up a fuel injector -- in the process of diagnosing this, it's clogged injectors over a half-dozen times. The particles are small and mostly ferrous, and only collect in the servo. The gascolator screen is completely clean.

A few things we've eliminated.

• Whenever my mechanic cleans the injectors and screen, he runs gallons of fuel through the boost pump and it all comes out clean.
• Happens with a brand new Weldon boost pump. (The 17-year-old Dukes gave up halfway through troubleshooting.)
• Definitely not the injectors; those are too far downstream and we replaced them anyway since the screens were shot.

The engine has ~50 hours on it and the mechanical fuel pump, servo, and flow divider are all overhauled. They could be a problem as we haven't changed them out yet.

Has anyone seen anything like this?

First photo is the initial pile of junk we removed from the fuel servo screen. Mostly ferrous.

Second photo is the next pile we removed after 0.5-1.0 hours on the engine. Same material.

[carusoam]

How did you identify... ‘mostly ferrous‘?

Best regards,

-a-

[MB65E]

Same fuel source?  I’d flush the tanks and get some fresh fuel from some other place. 

-Matt

[adverseyaw]

1 hour ago, carusoam said:

How did you identify... ‘mostly ferrous‘?

Some of it stuck to a magnet, but not all of it.

1 hour ago, MB65E said:

Same fuel source?  I’d flush the tanks and get some fresh fuel from some other place. 

That's on my list but given that we've dumped 20 gallons through it already (and the boost pump runs a gallon or two clean after every cleaning), I don't have my hopes up. :-(

[carusoam]

AY,

Did you identify anything upstream in the tanks or in the fuel strainer screen?

• this may help identify the source of the bits
• older mooneys has mild steal fuel necks where the fuel caps were seated.  Rust showed up downstream.

 

See if @M20Doc has seen this before...   

• fine particles.
• making it’s way through the various screens.
• has blocked at least one fuel injector.
• some ferrous, but not all. Indicating more than one source, or some ‘composite’ structure falling apart.
• pretty serious technical challenge when it has blocked a fuel injector.

Private pilot reporting the OP’s actual observations. Not a mechanic...

Best regards,

-a-

[MB65E]

I’ve pumped fuel before where it looks fine going in to the tank. However when you filter it thru a white terry towel, it turns black. This happened due to contamited fuel at a major military Airshow where normally 100LL was not available. The Airshow contracted the fuel from an oil company and not an FBO. We ran the fuel all week until we started having engine issues. It completely destroyed one performers engine. Ours was ok but ran poorly. That’s when I filtered the fuel and was shocked!! It was like metal sand!

I’m not saying that’s the case with yours but it looks similar! Almost exact.

-Matt

[Yetti]

How old are you fuel hoses?

Edited March 16, 2018 by Yetti

[RobertGary1]

I’ve had debris like that from old hoses. Changing the two hoses between the firewall and the servo isn’t very expensive and you can sign it off yourself as preventative maintenance. 

-Robert 

[adverseyaw]

These are all great ideas... a few things we've checked in response:

• Fuel hoses are the new brown silicone ones
• Fuel cap flanges seem to be OK, and so far the particles don't look like rust

 

Current theory we're evaluating is that we have some residual particles being caught in the servo screen, but the particles in the injector are coming from either the servo or the flow divider. (Of those, servo is much more likely candidate. Not much in the flow divider to go wrong.)

Thanks all so far

[Yetti]

How old is the mechanical fuel pump?  I don't think there is anything in there but the diaphragm and the alum walls.  The tanks don't make sense since the pickup is an above the bottom and has a screen on it.   But you might stick a phone down there take pictures to check.

[EricJ]

I had a bunch of issues like this when I first got my airplane.   The finger filter in the fuel servo had a bunch of rust-ish crap in it that turned out to (probably) mostly have been sourced from the fuel servo itself, after it had apparently been parked with water in it for a substantial period of time.   For me it ultimately wound up being fixed with a servo rebuild.   Other things to check are the gascolator filter and the fuel filter at the boost pump, if there is one.   If there's nothing in either of those, it may not be coming from the tank.

 

 

Edited March 17, 2018 by EricJ

[carusoam]

More of the example of the rusty fuel necks...  because if these tiny metal particles came with the fuel one day, the behavior may be the same...

• the fine rust particles were of various tiny sizes.
• the first place they showed up was the fuel drains.
• They had the ability to block the drain, or keep it stuck open and dripping.
• the next place the particles showed up was below fuel separator screen.  This was found and cleaned at annual inspection.
• Stainless fuel necks are pretty easy to identify. Shiny, smooth, clean, probably non-magnetic... compared to the mild steal version. 

It would be great if you can identify the bits further upstream. This would indicate that the bits came with the fuel...

Even though they are metal particles they seem to travel pretty far and sneak through some pretty fine screens.

I never noticed the particles further down stream.  Doesn’t mean they didn’t get that far...

PP experience only from my Old M20C, not a mechanic...

Hope that can help...

Best regards,

-a-

[Guest]

On 2018-03-15 at 11:38 PM, adverseyaw said:

I'm stumped and could use a hand with my IO-360 in my 1978 M20J.

I'm collecting small particles in my fuel servo strainer. Occasionally some sneaks through and clogs up a fuel injector -- in the process of diagnosing this, it's clogged injectors over a half-dozen times. The particles are small and mostly ferrous, and only collect in the servo. The gascolator screen is completely clean.

A few things we've eliminated.

• Whenever my mechanic cleans the injectors and screen, he runs gallons of fuel through the boost pump and it all comes out clean.
• Happens with a brand new Weldon boost pump. (The 17-year-old Dukes gave up halfway through troubleshooting.)
• Definitely not the injectors; those are too far downstream and we replaced them anyway since the screens were shot.

The engine has ~50 hours on it and the mechanical fuel pump, servo, and flow divider are all overhauled. They could be a problem as we haven't changed them out yet.

Has anyone seen anything like this?

First photo is the initial pile of junk we removed from the fuel servo screen. Mostly ferrous.

Second photo is the next pile we removed after 0.5-1.0 hours on the engine. Same material.

Does your plane have the inline filter after the Dukes pump?  It’s an cylinder about 1-1/2” x 5 long.  Many don’t know they have one or what it is.  Depending on your Dukes part number the filter was installed by an AD and SB.

Clarence

[adverseyaw]

On 3/16/2018 at 6:40 PM, Yetti said:

How old is the mechanical fuel pump?

It was overhauled this time last year and has 50 hours on it since then, not sure its age before that. Talking with my mechanic and engine builder, we're thinking the fuel pump is the most likely culprit.

On 3/16/2018 at 6:56 PM, EricJ said:

I had a bunch of issues like this when I first got my airplane.   The finger filter in the fuel servo had a bunch of rust-ish crap in it that turned out to (probably) mostly have been sourced from the fuel servo itself, after it had apparently been parked with water in it for a substantial period of time.   ... Other things to check are the gascolator filter and the fuel filter at the boost pump, if there is one.   If there's nothing in either of those, it may not be coming from the tank.

These are great ideas -- it seems like the screens upstream of the servo all have larger openings. The servo screen is the finest one and seems to catch the sandy particles from further up.

(My mechanic also mentioned they look a lot like blasting media.)

On 3/16/2018 at 7:13 PM, carusoam said:

More of the example of the rusty fuel necks...  because if these tiny metal particles came with the fuel one day, the behavior may be the same...

• the fine rust particles were of various tiny sizes.
• the first place they showed up was the fuel drains.
• They had the ability to block the drain, or keep it stuck open and dripping.
• the next place the particles showed up was below fuel separator screen.  This was found and cleaned at annual inspection.
• Stainless fuel necks are pretty easy to identify. Shiny, smooth, clean, probably non-magnetic... compared to the mild steal version. 

It would be great if you can identify the bits further upstream. This would indicate that the bits came with the fuel...

Even though they are metal particles they seem to travel pretty far and sneak through some pretty fine screens.

No doubt. I've only seen one or two flakes come out of the fuel drains in the last month or two but my A&P will be clearing the finger strainers in the tanks and will see if there's anything in there.

9 hours ago, M20Doc said:

Does your plane have the inline filter after the Dukes pump?  It’s an cylinder about 1-1/2” x 5 long.  Many don’t know they have one or what it is.  Depending on your Dukes part number the filter was installed by an AD and SB.

Clarence

Yep, it's got the Dukes filter. We haven't seen anything in there so far, although the holes in the screen are a lot bigger than the fine screen in the servo (which is where everything is getting stuck.)

Thanks all above, this is helping us nail this down.

An update based on what we've found and things we've tried:

• The servo inlet filter crud may be sand or blasting media. It may be coming from the mechanical fuel pump.
• The junk in the injectors is coming from the servo or flow divider, OR it's coming up further upstream (the fuel pump) and the servo inlet screen is getting clogged enough that the bypass spring is letting it through.

Unfortunately the extent of clogging so far means that once we identify and clear the source, we're going to have to disassemble and clean the mechanical pump, servo, and flow divider.

 

[RobertGary1]

Have you checked the undocumented “secret” filter at the electric pump?

 

-Robert

[carusoam]

RG,

Is that the same filter mentioned in the line above yours...?   “Yep, it's got the Dukes filter.”

This is one tough mystery.

Best regards,

-a-

[adverseyaw]

I'm curious as well to know which one that is :-)

I pulled the Dukes pump out last week and installed a Weldon. No filter in the pump head but I think my mechanic pulled the screen nearby.

[RobertGary1]

There was an SB calling for a filter between the electric pump and the back of the firewall. This was to prevent engine failures if the electric pump shreds. I've seen a lot of Mooneys that had this filter added but not all have it. It just looks like a wider part of the fuel line to account for the filter.

 

-Robert

[RobertGary1]

This is the SB that allowed the secret filter...

http://www.mooney.com/en/sb/M20-222B.pdf

Here is a thread where I have pictures..

-Robert

 

[tony]

I never understood why the FAA allowed this SB.  Lets put something in the line that can restrict  fuel flow. 

The right thing to do was to replace the dukes with a Weldon pump.  

[jetdriven]

On 3/16/2018 at 9:53 AM, MB65E said:

I’ve pumped fuel before where it looks fine going in to the tank. However when you filter it thru a white terry towel, it turns black. This happened due to contamited fuel at a major military Airshow where normally 100LL was not available. The Airshow contracted the fuel from an oil company and not an FBO. We ran the fuel all week until we started having engine issues. It completely destroyed one performers engine. Ours was ok but ran poorly. That’s when I filtered the fuel and was shocked!! It was like metal sand!

I’m not saying that’s the case with yours but it looks similar! Almost exact.

-Matt

WHOA !