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mysterious fuel leak

glider_rider

Active Member
I'm having a hard time to find a root cause of leak from injector on cyl 2 on my IO-390 EXP 119. I'm pretty sure the injector is installed and torqued properly. The A letter mark is on the bottom side.
Did a quick test: removed the cowling and covered the injector with a piece of cloth, then run the engine for a few minutes. The cloth was dry, which would suggest that on the ground the injector doesn't leak. Nevertheless after a few hours of flight traces of fuel indicate that something is seriously wrong.
Is it possible that somehow fuel is sucked out of the injector's screen?
thanks in advance for any help
 

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Let’s talk about this

I'm having a hard time to find a root cause of leak from injector on cyl 2 on my IO-390 EXP 119. I'm pretty sure the injector is installed and torqued properly. The A letter mark is on the bottom side.
Did a quick test: removed the cowling and covered the injector with a piece of cloth, then run the engine for a few minutes. The cloth was dry, which would suggest that on the ground the injector doesn't leak. Nevertheless after a few hours of flight traces of fuel indicate that something is seriously wrong.
Is it possible that somehow fuel is sucked out of the injector's screen?
thanks in advance for any help

How do the EGT's and CHT's look? Fuel flow at 75%, 100 ROP? Does the engine run well, without erratic misfires?

In the meantime, I’m going to have a close look at mine.

Bill
 
#2 is the hottest cylinder, but CHT stay well below Lycoming's red line.
The engine does indeed run somewhat erratic on low rpm, say below 1000 rpm, but on the other hand flat out I can easily exceed 190 knots. On high rpm the engine runs like a Swiss watch.
 
When new, mine was a little rich at idle and ran noticeably rough. Aggressive leaning helped and I adjusted idle mixture on the servo. I still lean on the ground, but it’s much better. Flying, it’s smooth and strong. #2 is the hottest, by a little, on mine as well. I have some theories about the residue around the injector, but don’t know for sure.
By the way, my #2 injector looks very similar to yours!
 
#2 is the hottest cylinder, but CHT stay well below Lycoming's red line.
The engine does indeed run somewhat erratic on low rpm, say below 1000 rpm, but on the other hand flat out I can easily exceed 190 knots. On high rpm the engine runs like a Swiss watch.

CHTs well below Lycoming redline isn’t saying much.. Lycoming redline of 500*F is crazy.. most people consider 420 to 430 a more realistic limit..
 
#2 CHT is ca. 340-350 while other ones are 10 deg cooler
 

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I would clean the area close to the injector.
My two cents, this happens on GND after fuel cut off.
It could be fuel left in the divider and heat push whats left there.
Try to run 1,000 rpm and then pull mixture.

Good luck
 
I would clean the area close to the injector.
My two cents, this happens on GND after fuel cut off.
It could be fuel left in the divider and heat push whats left there.
Try to run 1,000 rpm and then pull mixture.

Possibly...
Or it could be from air disturbance from the air blast directed onto the injector.

The left side front air dam supplied with the baffle kit has a block out area located directly in front of the #2 injector. I see that you do not have the dam installed (though maybe you removed it to take the photo?)
I think it would help with this.
The company prototypes have the air dam trimmed down somewhat but the portion that is in front of the injector body is left full height.
 
could be normal. At shut down after a flight, the under cowl temps get pretty hot. The fuel in the SS lines boil and this pushes the fuel towards the injector. Can't go the other way due to ICO. Most of it goes past the restrictor, but some does go out of the vent screen.
 
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Possibly...
Or it could be from air disturbance from the air blast directed onto the injector.

The left side front air dam supplied with the baffle kit has a block out area located directly in front of the #2 injector. I see that you do not have the dam installed (though maybe you removed it to take the photo?)

That's exactly right, I removed the air dam to take a better shot at the fuel residue
As cylinder #2 is the hottest one, I was thinking about trimming the air dam just a little bit to let the ram air around that last fin. Is it good idea?
 

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That's exactly right, I removed the air dam to take a better shot at the fuel residue
As cylinder #2 is the hottest one, I was thinking about trimming the air dam just a little bit to let the ram air around that last fin. Is it good idea?

Sure
Every engine is a little bit different, so they are not meant to be necessarily used exactly as supplied, but they were designed to be big enough, and then able to be trimmed down as necessary.
Before committing to trimming some people, remove them and temporary early, install aluminum tape to find a final size and then transfer that to the dam.
 
Son-of-a-gun!

Possibly...
Or it could be from air disturbance from the air blast directed onto the injector.

The left side front air dam supplied with the baffle kit has a block out area located directly in front of the #2 injector. I see that you do not have the dam installed (though maybe you removed it to take the photo?)
I think it would help with this.
The company prototypes have the air dam trimmed down somewhat but the portion that is in front of the injector body is left full height.

Mine doesn’t have the left air dam at all! 🤔

E04A8DED-87B5-435A-B2F7-587B1877E527.jpg
 
Unscrew the B nut on the injector and inspect the line. It could have a small crack in it especially around the weld. We had one that broke then found out there is an AD for inspection of these lines on Lycoming engines.
 
A little bit of fuel dribble staining is typical for this type of injector, especially with Bendix type systems. After shut down, any remaining fuel in the lines can vent out through the bleed holes and appear to be a leak Are the injector bodies properly orientated with the bleed hole facing up hill? Also, its possible during flight operations for low pressure inside the cowling to suck fuel out of the bleed hole depending on its orientation.
 
Sebastian,

I see this often on injectors. If on all cylinders, it suggests over priming. Otherwise, indicates as mentioned before airflow or air pressure that sucks fuel out of the dirt bell on the injector body. This would also cause a higher EGT on that cylinder.

Try running without the air dam on the baffle. It could be causing disrupted flow or low pressure consentrated at the injector. If so trimming it may stop the issue.

I also see this on a regular basis when a plenum is installed.
 
I have seen fuel stain on all of my injectors body but that maybe due to the fact that the vent hole might not be positioned correctly and it is so little that I have not felt it is worth removing and reinstalling again.

In regards to the dam on #2 cylinder, I trimmed the portion of it that covers the cylinder, practically all of it so the air can get to the bottom part of my cylinder. My CHTs of C1, 2 and 4 are within 4-6 degree of each other now and #3 about 10 degree cooler than the rest.
 
I have seen fuel stain on all of my injectors body but that maybe due to the fact that the vent hole might not be positioned correctly and it is so little that I have not felt it is worth removing and reinstalling again.

In regards to the dam on #2 cylinder, I trimmed the portion of it that covers the cylinder, practically all of it so the air can get to the bottom part of my cylinder. My CHTs of C1, 2 and 4 are within 4-6 degree of each other now and #3 about 10 degree cooler than the rest.

Would you have a picture of your trimmed down dam for cylinder # 2?
 
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Would you have a picture of your trimmed down **** for cylinder # 2?
Hi Glen,
I will take a picture in the next day or so but simply, I cut the portion that touches the cylinder minus the part that blocks the injector. If you look closely, that portion of the cylinder's fins, does not have any depth so air does not easily get to the bottom part of the cylinder thru the fins.
With some tweaking here and there, here is a sample of my CHTs but number 3 is typically cooler than the other but I am fine with that.
 

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Hi Glen,
I will take a picture in the next day or so but simply, I cut the portion that touches the cylinder minus the part that blocks the injector. If you look closely, that portion of the cylinder's fins, does not have any depth so air does not easily get to the bottom part of the cylinder thru the fins.
With some tweaking here and there, here is a sample of my CHTs but number 3 is typically cooler than the other but I am fine with that.

Wow. Those are great temps. So did you remove the portion that I have marked up below?
 

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Removal of cyl. 2 air dam

Since I do not have an injector in the top section of the cylinder (Mine is in the bottom prime port, EFII) I completely removed the air dam. Attached readings taken with and without the air dam similar conditions. Looking at a 30 min sections of similar flights for 30 mins the delta between Cyl. 1 and 2 was 13.55 degrees average before the dam was removed and 6.40 degrees F after the dam was removed. Delta between 2 and 4 same time period was 31.54 dam in vs 24.11 dam removed. Not as good as some have seen but any reduction in 2 CHT is better. (I think)
 

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