Leaking fuel injectors -weird gami spread

[aaronk25]

So a few of us have struggled with our J's at wide open throttle and fuel staining around the injectors or gami spreads bouncing all over. Backing off the throttle .5" of MP fixes the issue, but who wants to do that? It seems at wide open there isn't enough pressure differential between outside air and intake pressure to over come the air hitting the fuel injector at 130-150kts and the result is fuel bring drawn out of the air bleed hole on the fuel injector instead of air getting sucked in to help with fuel atomization.

These are made out of 1" 20gauge angle and held securely in place with high temp silicone RTV 650f rated.

At 1" dimension these are positioned in the last cooling fin near the injector as to not block cooling air.

Also if #1 and #4 are running hot you can cut down the baffle on number 1 and bend up the baffle on #4 to get some more air over the top of the cylinder.

No more staying and rock solid GAMI spread at full throttle.

[PTK]

Looks like a band-aide approach.

Is it legal?

What's the reason for your problem?

I'm running stock injectors WOT with no issues. None. Gami spreads ~0-0.2 gph. Deep lop.

[aaronk25]

PTK - I don't like you. Nor the way you respond to others. Do me a favor and never comment on any of my posts, ok and I'll extend you the same courtesy.

[PTK]

That's a wonderful opinion of yours and thank you for sharing it. Regretfully, I will not consider it important.

I will participate on any forum and comment on any post I so choose.

[Guest]

Aaron,

I'm confused as to the purpose of the little deflectors on cylinders.

As to the leaking from the vent holes in the injectors, are they installed per SI1275C?

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

Clarence

[N201MKTurbo]

Normally there will always be airflow from the upper cowl into the intake port through the injector. The manifold pressure is always lower then ambient and there is a pressure rise above ambient in the upper cowl from the ram effect.

There would need to be something wrong somewhere for the pressure in the intake port to rise above the pressure in the upper cowl. That is the only way fuel could be blown out the vent hole during WOT operation in flight.

I suppose that if you were running it on the ground with the upper cowl off, there could be some localized low pressure areas from the prop wash that could cause the reversed airflow through the injectors, but this would not be representative of real world conditions.

[aaronk25]

Yes the bleed holes are faced up. It's a bit difficult to orientate the injector and not exceed torque spec but managed.

The deflectors don't allow the 130-160kts air to directly hit the injector. Which then creates enough low pressure on the back side of the injector to suck fuel out the bleed hole. This only happens at WOT, if mp is reduced even 1/2" it's a non issue.

Even gami is aware of this issue on m20js. It also seems better with a more restrictive bracket air filter installed vs the challenger (k&n style filter). Was never a issue when ram air was operative as I think the way the air filter is positioned and the larger size of the filter vs the small ram air intake, the filter induction gets a big blast of air from the prop.

[Shadrach]

Aaron,

I am sorry to see that your injector issue is still present. I am puzzled by it. I just can't see how you're getting greater than ambient pressure inside the manifold anytime the engine is running. I can get my head around a low pressure area in the cowl, but given that the injectors are oriented properly, we know that's not the issue.

[N201MKTurbo]

So here is the ultimate fix...

Install a set of turbo injectors, route the vent lines to fitting between the air filter and the servo. This would get you the correct pressures all the time, and besides if it did leak you would never know it.

[aaronk25]

Turbo there is a good idea! I'll talk to john Paul at gami. He is well aware of the issues some 201s have.

I have a jpi 830 and have been doing the mp calculations at altitude and the best I can tell my MP at WOT is identical to the pressure at the current altitude.

This amazes me as I remember flying the 182 and I'm at least 1.5" greater at any altitude.

Like I said before if I choke off the intake by running a more restrictive filter it's fine, but why take the performance hit?

This thing screams and will lay down 165kts at 8,500ft so it would be undesirable to reduce cruise by a few kts.

[MB65E]

Some of the faster Continental N/A Lancairs had "refrance" lines on fuel injector systems. This line measured clean air into the cowling. As the airplane accelerated the pressures in the cowls changed enough the throw the fuel mixture off. Makes sense to me...

On other Lycoming installs, I bet the air is dirty enough to not have issues with the venting like you are having.

As for the legality, I'd be a bit careful. You might consider asking Gami for a letter or something.

I've had some success with running a bit back from WOT. I run mine at WoT, then pull back the throttle slowly until I notice the mP decrease. This usually works out to about 1 gal if fuel savings. This might be enough to still run at Max MP but reduce the fuel enough that it doesn't leak.

Sounds like you have one nice rocket ship!!

Good luck!

-Matt

[Guest]

Aaron,

You say GAMI knows of the issue, is this effect only with their nozzles? Does the same happen with Lycoming nozzles?

Clarence

[PTK]

Aaron,

You say GAMI knows of the issue, is this effect only with their nozzles? Does the same happen with Lycoming nozzles?

Clarence

And how much does the IO360 in the J really benefit from GAMI injectors?

[Shadrach]

And how much does the IO360 in the J really benefit from GAMI injectors?

It depends on the engine. While many run fine with stock injectors (mine does), I've heard that some of the factory new engines have had troubles. I think GAMIs are great, but only if you need them.

[jetdriven]

I fabricated an air dam in front of #2 and removed the oil cooler baffle completely. FWIW my #2 has the F injector in it (the largest) and it still peaks first.

[aaronk25]

I think I might have went over board putting them all on as it was the #2 and sometimes #3 that have the symptom. There easy to remove.

I really like the idea of turbo nozzles just not sure how I could get gami to sell them to me as I'm sure it wouldn't comply with Faa regs as they haven't been "certified" for my engine.

The other interesting thing is that at ROP power settings it doesn't occur only at peak or slightly lean of peak so I believe the reduced fuel flow though the injector reduces the pressure drop inside the injector which is when they bleed out slightly.

[Shadrach]

Aaron,

I'm not trying to pee in your cheerios on this, but I just don't see how reducing fuel flow does what you say it's doing. The injectors are vented to ambient pressure. When the engine is at full throttle, the fuel pressure at the injectors isn't pushing fuel into the manifold it's merely providing a metered volume of fuel that is drawn in by the constant state of vacuum that exists inside the manifold of a normally running NA engine.

[N601RX]

The intake vacuum isn't smooth and constant. Pressure spikes, poth peaks and valleys are generated as the intake valve opens and closes. It's also very unlikely that the fuel flow is steady either due to the changing pressures in the intake. When you accelerate and decelerate fluids quickly the pressure also changes.

[aaronk25]

Isn't the bleed hole above where fuel is introduced and streaming by so the more velocity of fuel the more negative pressure when compared to ambient, inside the injector between the bleed hole and the fuel streaming though? There is a air chamber inside the injector about 3-5mm where the fuel sprays from the metering nozzle into the end of the jet and air is pulled in? Correct?

[N201MKTurbo]

No, if you run the injectors out of the cylinders they will just make a stream of fuel like a squirt gun. The air flow through the injector nozzle atomizes the fuel stream. The air flow through the injector nozzle is caused by the pressure differential between the vent hole and the intake port.

[jetdriven]

Iirc the injector mixed air drawn in through that bleed hole to atomize the fuel. My #2 was spraying fuel all over the cylinder and nothing stopped it until I made the air dam. 200 mph air was going past the body and sucking fuel out of it.

[Shadrach]

No, if you run the injectors out of the cylinders they will just make a stream of fuel like a squirt gun. The air flow through the injector nozzle atomizes the fuel stream. The air flow through the injector nozzle is caused by the pressure differential between the vent hole and the intake port.

 

Si Senor! ^^^^^This is my understanding of how injectors work on a normaly aspirated engine.

[Guest]

I fail to understand how this happens. The pressure within the cowl at high cruise speed will be higher than the air pressure(manifold pressure) in the intake port where the nozzles deliver fuel. This pressure differential is what draws air through the bleed hole. Fuel normally dribbles out the bleed hole on shut down only when the nozzle is installed other than in accordance with SI 1275C.

Clarence

[larryb]

I think it is the Venturi effect and not static pressure causing the problems. I have noticed blue around my #3 and that is my leanest by far. I'm gong to look further into this. Thanks for the thread!

[PTK]

Aaron,

I'm not trying to pee in your cheerios on this, but I just don't see how reducing fuel flow does what you say it's doing. The injectors are vented to ambient pressure. When the engine is at full throttle, the fuel pressure at the injectors isn't pushing fuel into the manifold it's merely providing a metered volume of fuel that is drawn in by the constant state of vacuum that exists inside the manifold of a normally running NA engine.

Ross, I thought it was about corn flakes!