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EFI Fuel Filter Contamination

R

rv6ejguy

Well Known Member
We've seen or heard of several incidences of fuel filter contamination recently now and present some photos and information with what we've learned so far.

In all cases, the filters are 40 micron SS mesh type.

Photo 1 is a pre-pump filter showing 'normal' construction debris. 100LL fuel USA.

Photo 2 is a post filter showing the dark goo others have reported. 100LL fuel USA.

Photo 3 is a pre-pump filter showing microbial contamination (lab determined to be aerobic and anaerobic). Mogas fuel. Spain.

We are not sure what the plugging medium is in the second photo or those involved from other reports or observations, usually dark in color.

It seems that water present in the fuel during storage on in the aircraft tanks can precipitate microbe growth. Ethanol may also add an oxygen component that facilitates growth of certain bacteria strains.

One may consider a biocide developed for aviation such as Biobor: https://www.biobor.com/products/biobor-jf-aviation/

We have seen at least two incidents with the post filter contaminated but not the pre-pump filter so there are still some unanswered questions.

I'll post more info as we learn more.
 

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Mike S said:
Any chance the 100LL is eating something inside the pump?
Click to expand...

I have several customers with over 1000 hours on their systems, exclusively 100LL fuel, one with 1700 hours. No pump or filter problems reported in those.

Most of the problems have occurred in less than 100 hours after new build or filter servicing.

As a side note, the microbial goo isn't well cleaned by flushing and compressed air, ultrasonic cleaning seems to work better, but nothing is better than a complete replacement. The elements are not expensive.

We are not sure at this point if we have multiple types of contamination happening here. I hope to have some info on the debris in photo 2 later this week, at least if it's ferrous or not. See if we can rule out pump gearset parts or not.
 
I had over 850 hours of trouble free service over 8 years from my 6A all on 100LL.. Then last fall I suffered two engine stoppages due to plugging all 4 injectors. Servo stainer Filter had both white and black contamination (mostly white). Pre-pump filter was spotless clean as well as tanks. Mech fuel pump internals heavilly coated with white out growth things. Never seen anything like it. Hanger neighbor had a similar problem at the same time, but suspected his issue was a degrading paper filter (white stuff looked fibrous to me and different than what I found in my plane) at the pump due to careless maintenance, but not sure. Can't help but wonder if there has been a substitution of an additive in the 100LL causing these issues, possibly more aggressive that is attacking rubber paper and aluminum. I had never heard of microbial growth in gasoline, only diesel, untill this post.
 
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Thanks for your post Larry. We have also not seen this issue until last year, being involved in aviation EFI since 1995 with nearly a million flight hours. Seems to be a recent development so something must have changed.

I also didn't know this was a thing with gasoline, only jet and diesel before, but seems like it's been well known since the '80s. Another gap in my knowledge obviously...

As mentioned, we may have more than one thing going on here.

Lesson as I said in another EFI thread a couple weeks back, don't skimp on filter inspections and I'd recommend listening out for changes in pump note before you crank. This can be an indication that filters are starting to plug.

Anyone finding crud in their filters, please take a photo and share it here. If possible, run a magnet over it and see if the stuff sticks to it.
 
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Gotta be 200 million US cars with fuel injection. What sort of micron rating is typical in that fleet?
 
DanH said:
Gotta be 200 million US cars with fuel injection. What sort of micron rating is typical in that fleet?
Click to expand...

Looks like the typical tank "sock" is around 80 microns, give or take 20 microns. Many also have a further filter downstream.

This is a recent development we've noted. Never had one report from customers of this in over 900,000 flight hours until 2022 so not sure why this is showing up now in such big numbers compared to years past.

I just present this as a heads up and something that users should be aware of. I don't have many answers at this point.

In 2 cases, this was a rapid onset. Previous flight, no issues noticed, next flight, engine was leaning out at high power. Power was reduced and the pilots made their way back to the airport.
 
Ross, your photo #2 is typical of what I'm seeing in my post-filter at about 100 hours. I've gotten good results back-flushing it out with solvent and compressed air, but can't get all of it. After about 3 flushes I can see the filter beginning to show signs of pressure-collapse, and replace the element.

I run primarily 93E10, with some 100LL bought "on the road" during long trips.
 
airguy said:
Ross, your photo #2 is typical of what I'm seeing in my post-filter at about 100 hours.
Click to expand...

Thanks for your observations Greg.

I hope some more folks will tell me what they see in 100 hours of operation so we can determine what may be typical.
 
riseric said:
Greg,
Is your post pump filter also 40 micron ?
Click to expand...

Yes, I'm running a larger Holley filter, with the 162-566 element, 40 micron. I increased the size of my post filter about 800 hours back when I first saw a trend toward plugging.
 
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Thanks Greg,
I have a 10 micron post pump filter. I replaced it after the first year of flying, 70 hours or so, nothing strange observed.
I installed the same as I had it on hand. Was thinking of switching to 40 micron next time around though 10 works fine as of now...
No known issues yet.

So I will pay a lot more attention to pump noise on startup and in-flight fuel pressure from now on until next annual this fall.
Despite lots of driving, I don't recall an auto mechanic servicing or replacing fuel filters on my cars in the last 20 years, 2 of them 200,000 kms and more...
I wonder if the chemestry of avgas changed recently and is it USA only or more widespread?
 
I am looking at a disassembled 393 pump here and I see 2 possible sources of "Black Matter" that could find its way into the post pump filter.

#1 is the carbon brushes. They wear, the carbon dust goes into the fuel.

#2 is the outer gerotor housing which appears to be either nitrided and/or parkerized steel. It's hardened and shows zero wear in this example with about 150 hours on it.

Based on this, I'm guessing that much of the black we find in the downstream filter is brush carbon.

I had a 392 pump on a shop car for 19 years, 5000 hours estimated. Still working when the car was sold. Not sure how much brush length was left on that one or if brush material is the same now as it was back then.

Considering what we see in 100 hours trapped in the post filter, it seems like a lot for only 100 hours of operation.

Larry reported white residue in his filters, so that's different from what we mostly see.

The white and black residue is different from biological matter my Spanish customer had in his. Can see the green tinge there.
 
We swapped both the elements during our first annual last month with about 180 hours. I still have the old ones at home so I'll grab pics when I can. We saw nothing on either one except a few small pieces of proseal that were likely loose in the tanks from the build.
 
I have 600 hours on my current fuel pump module (Walbro 393's), which is split right at 50/50 timewise on each of the two pumps for 300 hours each. I always switch pumps when I switch tanks - so every gallon pumped from the left tank is on the left pump, etc. That way I can keep the time on each pump roughly equal and catch a weak pump before it's a critical failure point.

I did kill one pump at 420 hours on the original module (approx 210 hours per pump) by sucking air into the system (which these pumps don't like) and chose to replace both of them rather than just one. I had missed one natural rubber O-ring on a fuel pre-filter that was deteriorating from the ethanol fuel exposure, cracked and was sucking air. Those pumps got replaced back in October 2020 when I installed the current fuel pump module which now has 600 hours on it.

Care to pull mine apart to look at the 300-hour brushes? One of them?
 
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rv6ejguy said:
Larry reported white residue in his filters, so that's different from what we mostly see.

The white and black residue is different from biological matter my Spanish customer had in his. Can see the green tinge there.
Click to expand...

In my case, the white stuff was literally growing on all of the aluminum parts inside the AC mech fuel pump. I can't imagine that this was a bad casting and instead assume something in the fuel created a reaction with the aluminum or one of it's alloying compounds. The white growth IMHO was not bilogical as it was too rough (looked like mountain ranges on a miniature scale) I am all but certain the that black was rubber particles (pulled a piece out of an injector and put under a 10X loup), but cannot be certain if it was the diaphragms in the pump or from a rubber hose, both of which were about 5 years old. It is clear to me that something in the fuel caused this, but can't prove it nor speculate on what it was. Clearly the debris quantity was significant, as it forced the servo screen to plug and bypass (I clean it at every CI), though I can't be certain this was the case and instead there could have also been growth inside the servo. I have yet to have the servo torn down and instead made a small filter (100 mesh) to be installed just before the spider to catch all of the **** coming out of the servo. Obviously I replaced all of the rubber and the pump.

I asked AS to send the pump back to the manufacturer for investigation as I found it very odd. Needless to say, no one seemed to care.
 
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Got some pics. 175ish hours since first flight on 100LL.
 

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Ross, I am not familiar with that 393 pump. Does it have a teflon coating on the gerotor surfaces when new?

Have all the subject failures used gasoline with ethanol?

PM sent on why of the questions.
 
Whose filters?

Agent 4573, Can you give a little more detail? Whose filters, material of construction and micron rating?

Thanks
 
GSL393 Fuel Pump

BillL said:
Ross, I am not familiar with that 393 pump. Does it have a teflon coating on the gerotor surfaces when new?

Have all the subject failures used gasoline with ethanol?

PM sent on why of the questions.
Click to expand...
😊

Walbro GSL393 Inline Fuel Pump 155LPH (universal external pump) is what 99% of us are using both SDS and EFII.
 
BillL said:
Ross, I am not familiar with that 393 pump. Does it have a teflon coating on the gerotor surfaces when new?

Have all the subject failures used gasoline with ethanol?

PM sent on why of the questions.
Click to expand...

Smaller version of the popular 392 pump. Millions in use. No Teflon coating that I'm aware of.

5 of the 7 hard pump failures we've heard about have been with using mostly 100LL.

This discussion is mainly about filter contamination and most who have reported a rapid accumulation of debris have mainly or exclusively used 100LL as well.
 
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dmattmul said:
Agent 4573, Can you give a little more detail? Whose filters, material of construction and micron rating?

Thanks
Click to expand...

These were out of the Holley pre/post filters that came with the SDS system from Aerosport. Both are 40 micron stainless mesh.
 
Thanks

agent4573 said:
These were out of the Holley pre/post filters that came with the SDS system from Aerosport. Both are 40 micron stainless mesh.
Click to expand...

They looked stainless and was hoping the post filter was 10 micron stainless. Most of the 10 micron variety I see are cellulose which I prefer not to use. I know Ross recommends 40 micron for his injectors and he feels comfortable they will be ok which I respect. Fuelab makes a good filter with a 6 micron ceramic filter but prefer not to use this fine of filter for the post filter.

Again, thanks for the details of what you are using. Seems to be performing well for you.
 
Ross or others, can you comment on the need for the post-filter? My 2017 SDS EM-5 system has the integral sintered bronze filter (35 micron, if I recall correctly) on the inlet of the pump module, and NO post-filter.
Should I be looking to retrofit a post-filter for the safety of the injectors/regulator?

I clean the pre filter annually and have never found anything but a small amount of metal shavings and lint. Mixed diet of 100LL and 91UL auto gas with no ethanol.
 
jwyatt said:
Ross or others, can you comment on the need for the post-filter? My 2017 SDS EM-5 system has the integral sintered bronze filter (35 micron, if I recall correctly) on the inlet of the pump module, and NO post-filter.
Should I be looking to retrofit a post-filter for the safety of the injectors/regulator?

I clean the pre filter annually and have never found anything but a small amount of metal shavings and lint. Mixed diet of 100LL and 91UL auto gas with no ethanol.
Click to expand...

I have no post filter on my RV-6, 20 years, never an issue however Walbro/TI literature dating back to circa 2016 apparently, recommends a post pump filter. I only saw this recently when searching pump information. I will add one at my next annual in August.

Seems like some folks are seeing nothing and some are seeing quite a bit of debris post pump.

There may be 2 different factories in the US producing these pumps but it's not clear if each factory only makes certain models. Not sure if materials are different or changed over the years.
 
jwyatt said:
Ross or others, can you comment on the need for the post-filter? My 2017 SDS EM-5 system has the integral sintered bronze filter (35 micron, if I recall correctly) on the inlet of the pump module, and NO post-filter.
Should I be looking to retrofit a post-filter for the safety of the injectors/regulator?

I clean the pre filter annually and have never found anything but a small amount of metal shavings and lint. Mixed diet of 100LL and 91UL auto gas with no ethanol.
Click to expand...

I know my opinion doesn't count for much, but I've always ran a post filter in my projects, mostly offroad vehicles and track cars. The pre-filter is there to protect the pump from crud in the tank. The post filter is there to protect the engine if the pump ever decides to grenade itself. At least, that's my thinking on it.
 
Pressure drops

jwyatt said:
Ross or others, can you comment on the need for the post-filter? My 2017 SDS EM-5 system has the integral sintered bronze filter (35 micron, if I recall correctly) on the inlet of the pump module, and NO post-filter.
Should I be looking to retrofit a post-filter for the safety of the injectors/regulator?

I clean the pre filter annually and have never found anything but a small amount of metal shavings and lint. Mixed diet of 100LL and 91UL auto gas with no ethanol.
Click to expand...

When I tested several filters for pressure drop the bronze sintered filters had quite a bit more and lower filter media sq inches. Most filters where in the 0.2 psi at 40 GPH but the bronze sintered one I tested was 0.65. Granted there are tons of sintered brass filters out there. The 40-micron SS filters (cleanable cartridges) that many recommend seem to work well for this application from multiple suppliers. (Holley, Fuelab, Aeromotive) Very low pressure drop and large surface areas. The Fuelab and Aeromotive have built in AN6 fittings which I like, one less fitting to leak.
 
dmattmul said:
When I tested several filters for pressure drop the bronze sintered filters had quite a bit more and lower filter media sq inches. Most filters where in the 0.2 psi at 40 GPH but the bronze sintered one I tested was 0.65. Granted there are tons of sintered brass filters out there. The 40-micron SS filters (cleanable cartridges) that many recommend seem to work well for this application from multiple suppliers. (Holley, Fuelab, Aeromotive) Very low pressure drop and large surface areas. The Fuelab and Aeromotive have built in AN6 fittings which I like, one less fitting to leak.
Click to expand...

Pressure drop is very important in the input side of the pump - essentially meaningless on the output.
 
Yes

He was discussing his use of a sintered Pre-filter (input side of pump). Although it is interesting how users are clogging post filters which should be able to take 10 psi or greater pressure drop.
 
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We've heard of a few instances of pre-filters becoming contaminated as well so we know these ones are probably not due to anything the pump may be shedding. At least one case of both filters being partially plugged.

In the case of the Spanish customer, he had multiple events of this over the course of a year or so. He's the only one to have paid a lab to find out what the debris was so far. He had to know, to solve this before he had a forced landing. In his case, the onset was very rapid. Obviously disconcerting when it happens several times.
 
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