Leaking fuel injectors

[aaronk25]

So I wanted to bump the old post, and add some new info.  I previously posed about the blue fuel streaking down the sides of the cowl flaps, alot of fuel.  Turns out after talking with John Paul at Gami some other mooneys have had the same issue where when cruising low at full throttle, the high speed of air coming in the cowl can actually create a low pressure area behind the injector which causes fuel to come out the bleed hole.  If I back off the throttle 1/4"-1/2" in eliminates the fuel leak.  

 

The mechanic has had the cowl off 3 times and we are certain the fuel is coming from the injectors bleed hole. 

 

My bird has the Ram air deleted, but does have a challenger air filter installed and Gami seems to think either the induction system still gets some ram air or else the air pattern around the injector is actually creating the low pressure area.  Maybe its a little of both?.?  

 

So I am not sure which way the stamped letter in the Gami are oriented to the cylinder head.  I've read it the letter is supposed to be facing down toward the cylinder head which in turn would make the bleed hole face up toward the cowl.  I am going to check later and make sure the bleed hole is not facing the rear of the engine as I could see how the passing slip stream could create a low pressure area and allow fuel to exit.  

 

Does anyone have any idea if facing the hole towards the prop (stamped letter toward the cabin)  if that would help?   Gami said some experimental guys also made a shroud that went over the nozzle to keep air off it, anyone else have ideas how this could be done?  Maybe a hose clamp?  Obviously it wouldn't be certified but I really don't like the idea of cruising around with the throttle backed off 1/2" of MP.

 

Thanks for the help guys!!!

 

Aaron

 

 

[kmyfm20s]

M20turbo described it to me in another thread, maybe he will chime in here. As I understand the letter faces down and at a slight angle toward the deepest part of the solid recess(away from the cooling fins) to help equal the fuel atomization. They will be in diiferent direction Left to rigt side. Interesting because this would create positive pressure on the bleed hole on one side and negative pressure on the other. I will be curious to the responces you get. It would be great if people look at the orientation of their injectors and noted position and which ones had the most blue spray around them.

[Shadrach]

I cannot comprehend how your choice of air-filter or having/not having Ram air would cause this, in fact I doubt it has anything to do with the induction system at all.

[aaronk25]

I cannot comprehend how your choice of air-filter or having/not having Ram air would cause this, in fact I doubt it has anything to do with the induction system at all.

If the pressure inside the intake valve is the same as what is outside by the injector you get leaking fuel out the hole. I didn't say the air cleaner was the sole cause but I listed it because a challenger air cleaner is less restrictive. I would think the ram air would be even more so.

Your taking what I said out of context. Do you have any usefully information to offer?

[Shadrach]

If the pressure inside the intake valve is the same as what is outside by the injector you get leaking fuel out the hole. I didn't say the air cleaner was the sole cause but I listed it because a challenger air cleaner is less restrictive. I would think the ram air would be even more so.

Your taking what I said out of context. Do you have any usefully information to offer?

 

I'll try aaron, and I'm not taking what you said out of context.  Let's get a few things straight.

 

1) The injectors are screwed into cylinder intake plumbing just above the intake valve. This is an area of negative "pressure" (manifold pressure is suction) when the engine is running.

 

2) Backing off the the throttle causes manifold pressure to go down, which means the suction/vacuum in your intake manifold increases (this is why intake leak symptoms tend to manifest themselves at partial throttle).  

 

3) The bleed hole on the injectors is designed to help atomize the fuel going from the reducer to the nozzle, it also breaks the vacuum created at the injector at when the throttle is at idle. The air is drawn into the injector as the fuel passes from the reducer to the nozzle.  See the attached illustrations.

 

After taking in the above information, can you conceive of how changing air filters would matter in the least?  I have a hard time believing that John Paul would believe such a thing. If he did, I would ask for a detailed explanation.  It's the equivalent of holding a wet/dry vac under a faucet that is set to trickle and suggesting that .05% difference in suction would affect the water being sucked in.

 

I'm sure you're frustrated with the situation, but there's no need to be touchy with me for thinking out loud through my key board... 

 

It may be debris in the injector. I don't know...

 

I have 4 used injectors for an IO 360 that were over tightened by a ham fisted mx sometime between 1998 and 2008, so the area where the B-nut attaches is boogered. I would not consider them air worthy by FAA standards, but they should seal up just fine as they were not leaking when removed.  I will happily send them to you for testing if you'd like to do some ground testing to see is the problem remains with a different set of injectors.. 

[aaronk25]

I'll try aaron, and I'm not taking what you said out of context.  Let's get a few things straight.

 

1) The injectors are screwed into cylinder intake plumbing just above the intake valve. This is an area of negative "pressure" (manifold pressure is suction) when the engine is running.

 

2) Backing off the the throttle causes manifold pressure to go down, which means the suction/vacuum in your intake manifold increases (this is why intake leak symptoms tend to manifest themselves at partial throttle).  

 

3) The bleed hole on the injectors is designed to help atomize the fuel going from the reducer to the nozzle, it also breaks the vacuum created at the injector at when the throttle is at idle. The air is drawn into the injector as the fuel passes from the reducer to the nozzle.  See the attached illustrations.

 

After taking in the above information, can you conceive of how changing air filters would matter in the least?  I have a hard time believing that John Paul would believe such a thing. If he did, I would ask for a detailed explanation.  It's the equivalent of holding a wet/dry vac under a faucet that is set to trickle and suggesting that .05% difference in suction would affect the water being sucked in.

 

I'm sure you're frustrated with the situation, but there's no need to be touchy with me for thinking out loud through my key board... 

 

It may be debris in the injector. I don't know...

 

I have 4 used injectors for an IO 360 that were over tightened by a ham fisted mx sometime between 1998 and 2008, so the area where the B-nut attaches is boogered. I would not consider them air worthy by FAA standards, but they should seal up just fine as they were not leaking when removed.  I will happily send them to you for testing if you'd like to do some ground testing to see is the problem remains with a different set of injectors.. 

 

Thank you for the info.  I'm not sure I agree completely with you but I thank you anyway for taking the time to offer some more info to consider.  What I have going on for sure is there is not a large enough pressure difference between the intake and the area around the vent hole on the injector.  I've been busy lately winterizing toys and getting projects done before old man winter sets in but I'll get out to the airport tomorrow to check the orientation of the injectors.  I think is very conceivable that maybe the vent hole is in such an orientation that it is on the opposite side of the incoming cowl air which in turn is creating a low enough pressure area that a small amount of fuel is getting sucked out.  

 

The less restrictive air filter would allow the intake pressure to be higher than a restive counterpart.  I'm not saying, and neither is gami saying that is what it is, but when I asked John Paul about it he agreed it when narrow the margin between the 2 pressures.  How much closer, I don't know.  All it takes to stop the leak is closing the throttle enough to show a 1/4" reduction of manifold pressure, so if the difference between 2 filters is 1/4" then its a contributing factor, if it doesn't amount to that much, then its not.  

 

The injectors are not plugged as this has been a intermittent issue for the past year and the gami spead is .02gph same as it has been since installation.  I just don't know what else to check as these fuel injection systems are so simple there just isn't anything else to review, unless someone can point me to something.  

[Cruiser]

Aaron, 

 

When did this problem start? Was it something you just noticed after a flight that wasn't there before or was it after maintenance? What I am asking is looking for root cause. If you currently think the location of the injector vent hole is cause for the problem, why was it not leaking before? Were the injectors removed? Did the vents somehow change location?

 

You have more fuel under pressure than the cylinders are using and the excess is overcoming the external pressure outside the injector allowing the fuel to leak out the vent hole instead of air being drawn into the vent hole.

 

If it wasn't leaking before and it is leaking now, look for something that has changed. If the location of the vent hole on the injector has not changed It isn't the problem.

[Shadrach]

Aaron,

Did you ever get this sorted?

[N201MKTurbo]

I've been meaning to write about this. So the only thing that can cause your problem is higher pressure in the intake manifold then in the cowling. How can this be with a normally aspirated engine?

 

When the intake valve opens and air is drawn into the cylinder, it gives inertia to the column of air in the intake riser. When the valve closes the inertia of the air causes it to compress against the closed valve. This compression only lasts for a brief instant until the pressure increase exceeds the inertial force of the incoming air at which point air flow reverses direction. This oscillating pressure wave is what makes beer bottles sing when you blow across the top of them. During the brief instant when the pressure increases against the closed valve it must exceed the pressure in the cowl blowing some fuel out the vent hole.

 

the only thing that I can think of to reduce the effect without redesigning your cowl would be to point the injector vent hole into the wind. The pressure should be higher on the upwind side of the injector then the down wind side. Knowing the local airflow and pressures around the injector may be hard to figure out.

[Shadrach]

I think the bleed hole should be facing up. The only way to get a low pressure situation is if the hole is facing toward the firewall. There is NFW that MP at the intake port is going to be higher than ambient with the ram air deleted, challenger air filter or valve closure notwithstanding...

[N201MKTurbo]

I think the bleed hole should be facing up. The only way to get a low pressure situation is if the hole is facing toward the firewall. There is NFW that MP at the intake port is going to be higher than ambient with the ram air deleted, challenger air filter or valve closure notwithstanding...

So it must be fairies sucking the fuel out.....

[kmyfm20s]

The intake valve is only open on the intake stroke on a 4 stroke engine. There is definitely an opportunity for some back pressure through the vent hole of the injector. You might just slightly turn the injector in different positions to find the happy spot, but hard to do and stay with in torque specs.

[N601RX]

I've been meaning to write about this. So the only thing that can cause your problem is higher pressure in the intake manifold then in the cowling. How can this be with a normally aspirated engine?

 

When the intake valve opens and air is drawn into the cylinder, it gives inertia to the column of air in the intake riser. When the valve closes the inertia of the air causes it to compress against the closed valve. This compression only lasts for a brief instant until the pressure increase exceeds the inertial force of the incoming air at which point air flow reverses direction. This oscillating pressure wave is what makes beer bottles sing when you blow across the top of them. During the brief instant when the pressure increases against the closed valve it must exceed the pressure in the cowl blowing some fuel out the vent hole.

 

the only thing that I can think of to reduce the effect without redesigning your cowl would be to point the injector vent hole into the wind. The pressure should be higher on the upwind side of the injector then the down wind side. Knowing the local airflow and pressures around the injector may be hard to figure out.

What you are describing is very pronounced with water flow and is known as the water hammer affect.  I designed a test bench a few years ago to test product on that operates on this affect. With water flowing through a straight  pipe at around 30 psi we could generate a 400psi shock pulse when the valve was closed.   I could see the same thing happening with air to a much smaller extent.

[Shadrach]

So it must be fairies sucking the fuel out.....

No, there is an area of low pressure behind the injector.  Just like there is an area of low pressure behind the spinner... 

[Shadrach]

What you are describing is very pronounced with water flow and is known as the water hammer affect.  I designed a test bench a few years ago to test product on that operates on this affect. With water flowing through a straight  pipe at around 30 psi we could generate a 400psi shock pulse when the valve was closed.   I could see the same thing happening with air to a much smaller extent.

 

 

This is an apples to avocados analogy and does not apply.

 

1) The manifold is not pressurized. The open valve is drawing air in to fill the void as the piston travels away from the cyl head, it is not be forced in by above ambient "pressure".

 

2) I believe you're referring to a closed system, not a system with 3 other valves at in various positions also sucking in air.

 

3) For all intents and purposes, water is not compressible.

 

Would you see a pressure rise if you placed a closed a valve on the intake side of your compressor? That is a more congruous example and yet still falls short in many other aspects.

[N601RX]

This is an apples to avocados analogy and does not apply.  It does apply.

 

1) The manifold is not pressurized. The open valve is drawing air in to fill the void as the piston travels away from the cyl head, it is not be forced in by above ambient "pressure".

  IT doesn't matter if it is pressurized or not, It has air flowing through the pipe and the air has mass.  When the intake valve closes the air is moving foward intake pipe. The air has mass and will continue to try to move forward until it stops.  You will get a brief pressure increase until the movement stops

 

 

[kmyfm20s]

This is an apples to avocados analogy and does not apply.

 

1) The manifold is not pressurized. The open valve is drawing air in to fill the void as the piston travels away from the cyl head, it is not be forced in by above ambient "pressure".

 

2) I believe you're referring to a closed system, not a system with 3 other valves at in various positions also sucking in air.

 

3) For all intents and purposes, water is not compressible.

 

Would you see a pressure rise if you placed a closed a valve on the intake side of your compressor? That is a more congruous example and yet still falls short in many other aspects.

This is an apples to avocados analogy and does not apply.

 

1) The manifold is not pressurized. The open valve is drawing air in to fill the void as the piston travels away from the cyl head, it is not be forced in by above ambient "pressure".

 

2) I believe you're referring to a closed system, not a system with 3 other valves at in various positions also sucking in air.

 

3) For all intents and purposes, water is not compressible.

 

Would you see a pressure rise if you placed a closed a valve on the intake side of your compressor? That is a more congruous example and yet still falls short in many other aspects.

You are correct that the engine sucks air but that is only when the intake valve is open. With the intake valve closed you have the 150 kt ram pressure from the plane flying though the air. Even though it doesn't act as a solid like a liquid would it still adds pressure the same as if you put your hand out a car window. The ram pressure behind the closed intake valve has 3 choices. 1) staying in static equilibrium, 2) out the injector hole to an area of low pressure, or 3) back down the intake manifold to an area of low pressure created by an opposing piston on the intake stroke. Having just finishing an owner assist top end on my engine I have seen all 3 senerios. One of my intake was caked with blue inside the tube, and 2 of my injectors where squirting blue outside on to the cylinders.

[Shadrach]

You are correct that the engine sucks air but that is only when the intake valve is open. With the intake valve closed you have the 150 kt ram pressure from the plane flying though the air. Even though it doesn't act as a solid like a liquid would it still adds pressure the same as if you put your hand out a car window. The ram pressure behind the closed intake valve has 3 choices. 1) staying in static equilibrium, 2) out the injector hole to an area of low pressure, or 3) back down the intake manifold to an area of low pressure created by an opposing piston on the intake stroke. Having just finishing an owner assist top end on my engine I have seen all 3 senerios. One of my intake was caked with blue inside the tube, and 2 of my injectors where squirting blue outside on to the cylinders.

 If as you say, MP at the port is breifly raised above ambient, then why are we not all suffereing from injctors that leak in flight? What's funny about this analogy, is that while you make referrence to the enertia of air you make no no ref to the enertia of the constant flow of fuel at ~24psi.

 

I also beleive your mistaken in the notion that an engine breathing through a filter has a surplus of pressure at anytime due ram air.

 

 Also, your hand out the window analagy does not apply to anything inside the manifold.

[N601RX]

Here is an article that talks about what happens when the high speed air hits the closed intake valve. The 3rd paragraph describes what we have been discussing..

 

http://www.autozine.org/technical_school/engine/Intake_exhaust.html

[aaronk25]

Hi guys! I rotated the nozzles so that the bleed hole was facing towards the top of the cowl and slightly forward which shows the letter facing down. Every injector was previously torqued correctly but it resulted in the injector bleed hole facing down (on the low pressure side) with the letter facing up.

Fuel Leaking is down by probably 90 percent. I was nervous about how much pressure it took to crank the injectors around another 180 degrees, but I did it carefully and was able to gently coax them in to the proper the orientation.

Seems the previous leaking issue was more pronounced at high IAS, which I believe was a result of additional low pressure being created behind the injector, as mentioned previously.

Thanks for the help gentlemen!!!!

Aaron

[MB65E]

So the"A" was up prior? Now the A is down? What document says to have it down?All I have read was the A needs to be up. I shoot for 65 in lbs with some engine oil on the threads and try to point the A up... Never had any issues.

[jetdriven]

Lycoming SI 1275C says to put the "A" on the bottom and torque to 60 IN-LB. 

 

GAMI goes a little further and says to have the "A" within 30 degrees of the bottom. Mark the opposite flat with a sharpie and put that on the top since you cannot see the "A" when installed.

[tony]

Aaron, there is a Lycoming service bulletin that says the bleed hole needs to be oriented up.  see step 6.  Glad you got it sorted out.

 

http://www.lycoming.com/Portals/0/techpublications/serviceinstructions/SI%201275C%20(09-23-2008)/Cleaning%20Fuel%20Injector%20Nozzles.pdf

[MB65E]

Thanks for the Doc Tony any Byron.

I had thought the marked "A" (Air) was the location on the bleeder hole on the injector. I'll take one apart shortly and varify. I never knew is was 180 out. So bleeder hole up and marked "A" down.

Thanks Guys!

-Matt

[N201MKTurbo]

The letter indicates the orafice size. There are A, B and C injectors. The different injectors are for different fuel flow gage ranges when using the pressure gage connected to the flow divider for fuel flow.