Clogged Injector

[PT20J]

Here is what a clogged injector looks like (data from G3X EIS) on a Mooney M20J. I was cruising at 10,000' feet when the engine suddenly became rough.

 

You can see the dip in the EGT #1 trace when the injector clogged. This caused an increase in metered fuel pressure causing the servo to reduce fuel flow which leaned the other cylinders slightly and caused slight EGT rises. I responded by richening the mixture a couple of turns and then turning on the boost pump. You can see the EGTs drop when the fuel flow increases and you can see the fuel pressure rise when the boost pump is on. The clog cleared itself with the increased fuel flow and I returned the mixture to the original fuel flow and turned off the boost pump. 

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[kortopates]

that’s more of a full blockage, luckily only temporary. Full blockage like these are very rare. in a 4 cyl engine like this they can create an overly rich mixture in the other 3. which of course can lead to more severe problems.

Much more common to see a partial blockage leaning the cylinder rather than flaming it out.

Edited June 18, 2022 by kortopates

[Ragsf15e]

7 hours ago, PT20J said:

Here is what a clogged injector looks like (data from G3X EIS) on a Mooney M20J. I was cruising at 10,000' feet when the engine suddenly became rough.

 

You can see the dip in the EGT #1 trace when the injector clogged. This caused an increase in metered fuel pressure causing the servo to reduce fuel flow which leaned the other cylinders slightly and caused slight EGT rises. I responded by richening the mixture a couple of turns and then turning on the boost pump. You can see the EGTs drop when the fuel flow increases and you can see the fuel pressure rise when the boost pump is on. The clog cleared itself with the increased fuel flow and I returned the mixture to the original fuel flow and turned off the boost pump. 

Skip

So you must have been ROP with that ff at 10,000’, and it just went cold?  Seems pretty blocked.  Probably a little exciting.  Did you know exactly what it was at the time?

[ArtVandelay]

I had same thing happened on decent, I had reduced power for a decent . My EGT got so low the probe was marked bad and the JPI stopped recording it.

 

[PT20J]

13 hours ago, Ragsf15e said:

So you must have been ROP with that ff at 10,000’, and it just went cold?  Seems pretty blocked.  Probably a little exciting.  Did you know exactly what it was at the time?

This was actually the culmination of a little experiment. I used to clean the injectors every annual. Al Jesmer at Precision Airmotive suggested just cleaning them “on condition.” I wondered what condition would warrant cleaning them. So, I haven’t touched them since the rebuilt engine came from Lycoming about 350 hours ago.

On the trip down to MooneyMAX I noticed that the spread in FF between the first and last cylinder to reach peak EGT was greater than it had been - perhaps about 1/2 gph. On the return flight, I noticed that the fuel flow did not seem to change linearly when leaning and became somewhat erratic below 10 gph.  It seemed to like 10 gph which was a little rich of peak, so I left it there. 

When the event happened, there was a noticeable power loss and some roughness. But it wasn’t nearly as rough as when I had a SureFly (since removed) that had the 28v voltage spike problem and was cutting in and out. I was surprised that it wasn’t rougher running on three cylinders.

Given what I had previously noted regarding EGTs and fuel flow, I was pretty sure it was a fuel issue, so I just richened a couple of turns and turned on the boost pump which cleared it.

Back home, I checked the gascolator and servo inlet screens and both were clean. I removed the restrictors from the injector bodies and they looked OK except for cyl 3 which appeared to have something slightly restricting it. I soaked them in Hoppes and now the EGT spreads are back to normal.

So, I think the clog was either some sort of fuel decomposition gunk or lead. All the hoses are new teflon installed when we hung the engine.

I’m done experimenting and will henceforth clean the injectors at the annual inspection. But, it was an interesting learning experience.

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[ArtVandelay]

All my clogged injectors except above were after engine maintenance, buyer beware.  Most happen on startup.

[EricJ]

1 hour ago, PT20J said:

This was actually the culmination of a little experiment. I used to clean the injectors every annual. Al Jesmer at Precision Airmotive suggested just cleaning them “on condition.” I wondered what condition would warrant cleaning them. So, I haven’t touched them since the rebuilt engine came from Lycoming about 350 hours ago.

On the trip down to MooneyMAX I noticed that the spread in FF between the first and last cylinder to reach peak EGT was greater than it had been - perhaps about 1/2 gph. On the return flight, I noticed that the fuel flow did not seem to change linearly when leaning and became somewhat erratic below 10 gph.  It seemed to like 10 gph which was a little rich of peak, so I left it there. 

When the event happened, there was a noticeable power loss and some roughness. But it wasn’t nearly as rough as when I had a SureFly (since removed) that had the 28v voltage spike problem and was cutting in and out. I was surprised that it wasn’t rougher running on three cylinders.

Given what I had previously noted regarding EGTs and fuel flow, I was pretty sure it was a fuel issue, so I just richened a couple of turns and turned on the boost pump which cleared it.

Back home, I checked the gascolator and servo inlet screens and both were clean. I removed the restrictors from the injector bodies and they looked OK except for cyl 3 which appeared to have something slightly restricting it. I soaked them in Hoppes and now the EGT spreads are back to normal.

So, I think the clog was either some sort of fuel decomposition gunk or lead. All the hoses are new teflon installed when we hung the engine.

I’m done experimenting and will henceforth clean the injectors at the annual inspection. But, it was an interesting learning experience.

Skip

I had an injector clog on takeoff just after the gear came up, and the vibration was so bad I was worried that the engine mounts were going to hold together.   It's probably the difference between being at cruise or full power at low speed, but it was brutally rough.  I had about 100 ft/min climb left, so struggled around the pattern and landed.

In my case the finger filter in the servo was full of junk and we did blow a chunk of something out of the #2 injector.   No idea what it was, but this was right after I bought my airplane and there was a lot of deferred maintenance.   Even though it was straight out of an extended (four month long) annual, apparently the filters weren't checked as it appeared to be a lot of accumulated crap in the filter.

My cylinders aren't very well balanced according to my JPI, so I've been fiddling with cleaning injectors and moving them around for a long time, but nothing seems to matter.   I mention that only to say that myself and my current IA have noticed some recommendations to not clean the injectors too often since the cleaning process is a bit harsh.   The recommendations to not leave the injectors in the cleaning fluid too long seems to speak to that.   For this reason I've been back to "on condition" cleaning of the injectors, particularly since I never saw much difference from cleaning them, anyway, at least as far as balance was concerned.

Checking the filters, including the finger filter in the servo, at annual seems to go a long way toward preventing injector clogs, but evidently there's still stuff that can get in there.  I think the servo filtration is finer than the orifice in the injector restrictor, but maybe oddly-shaped stuff sneaks through or something.

 

[skykrawler]

I will attest to leaving the injectors in the Hoppes too long is a bad.    MEK will not eat the injector and you can take clean q-tip and insert it in the brass barrel and be surprised what will come out.  The bleed air hole in that brass barrel should be clear - that's where air is sucked in to atomize/spray the fuel that is metered in.

 

 

Edited June 20, 2022 by skykrawler

[A64Pilot]

In order to reduce the time the injectors sit in the Hoppes (some will let them sit overnight) I use an ultrasonic cleaner, they are cheap and once you have one you’ll find uses for it.

I believe an ultrasound will clean better with Hoppes than just soaking in Hoppes.

I put each injector in a baby food jar with Hoppes in the jar. Mark the jar to know who’s who. Leave the Hoppes in the baby food jars it’ll last forever in there.

15 min is plenty of time in an ultrasound

You can buy a Quart of Hoppe’s on Amazon for $17 and a quart is way more than enough

[PT20J]

On 6/19/2022 at 11:36 AM, EricJ said:

My cylinders aren't very well balanced according to my JPI, so I've been fiddling with cleaning injectors and moving them around for a long time, but nothing seems to matter.

Did you move around the entire injectors, or just the removable restrictors. It’s possible that someone previously mixed up the restrictors. The test, according to Precision Airmotive, is to run fuel through the injectors with the boost pump and note that the output is a tight stream. If not, you can try swapping restrictors around and see if you can match them up better. That’s how they match up the restrictors with the injectors at the factory.

Skip

[EricJ]

32 minutes ago, PT20J said:

Did you move around the entire injectors, or just the removable restrictors. It’s possible that someone previously mixed up the restrictors. The test, according to Precision Airmotive, is to run fuel through the injectors with the boost pump and note that the output is a tight stream. If not, you can try swapping restrictors around and see if you can match them up better. That’s how they match up the restrictors with the injectors at the factory.

Skip

I've treated them as matched sets, and swapped the assemblies between the hottest and coldest cylinders.    Since that had no effect there didn't seem to be a reason to look further at swapping them or mixing them up.    I did clean a couple of them, one at a time, a while back, also with no resulting changes.   I have gotten some results from fiddling with the baffling and cowl flaps, but nothing significant.   I have noticed that many J models on the ramps have larger baffles in front of the #2 cyl than mine has, and that's my cold cyl.   It seems to be non-factory baffling, but maybe that's the direction I need to start looking.

[kortopates]

On 6/19/2022 at 9:35 AM, PT20J said:

...

I’m done experimenting and will henceforth clean the injectors at the annual inspection. But, it was an interesting learning experience.

Skip

We recommend cleaning them only on condition. Starting with a clean injector baseline of your mixture you'll be able to tell when they need cleaning by the presence of a lean outlier or any significant lean shift in an injector (i.e. change in ranking). 100LL is pretty good solvent and the truth is the mere act of opening the system at the injectors to clean them is far more likely to introduce dirt into the system causing a partial blockage just as Tom @ArtVandelay mentioned above from his experience. If your mixture distribution is good, (hasn't worsened) then don't touch them. You can't make it any better but you sure can make it worse easily.

[PT20J]

4 hours ago, kortopates said:

We recommend cleaning them only on condition. Starting with a clean injector baseline of your mixture you'll be able to tell when they need cleaning by the presence of a lean outlier or any significant lean shift in an injector (i.e. change in ranking). 100LL is pretty good solvent and the truth is the mere act of opening the system at the injectors to clean them is far more likely to introduce dirt into the system causing a partial blockage just as Tom @ArtVandelay mentioned above from his experience. If your mixture distribution is good, (hasn't worsened) then don't touch them. You can't make it any better but you sure can make it worse easily.

I do understand how messing with stuff unnecessarily causes problems. I'm pretty much of a maintenance minimalist. But in this case, the symptoms only showed up around 5 hours before the clog in the middle of a 3500 nm trip. Stuff can happen anytime of course, but I would prefer that problems that can be prevented not occur on a trip. Greg Lehman at Advanced Aviation Services (MSC in Troutdale OR) recommends cleaning at 200 hr intervals. Since this one clogged at a bit over 300 hrs, I think that sounds like a happy medium between over maintaining and waiting for something to happen.

I suspect it is probably gum deposits formed when the gasoline oxidizes after shutdown that clogs them. The problem is that these deposits are not soluble in gasoline. 

I think the way to minimize any maintenance induced issues is to use the procedure recommended by Precision (which is what I did) and leave the injector bodies in the cylinders and just remove and clean the restrictors.

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