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Engine drops a cylinder. Head Scratcher. AFP?

Kahuna

Moderatoring
Need ideas for troublshooting.
IO-540, AFP.

Symptom,
Below 1500 RPM, #2 cylinder drops cold. Misses, no EGT, CHT drops.
~1500rpm, cylinder comes back alive, but is running ~100degF egt hotter than normal/others. Leaning it shows the cylinder continues to lean and peaks early indicating cylinder is lean. Mag checks good.

Bring RPM up higher ~2000rpm and the cylinder functions normally. EGT in line with others. Mag checks function as expected.

Actions so far.
1. Compression check hot and cold GOOD. 78/90
2. Swap injectors, swap injector lines around. Problem stays with the one cylinder. (I though for sure plugged injector.
3. Rockers snug, nothing unusual under rocker cover.
4. Oil change, filter clean.
5. Plugs look good.
6. Intake tube tight. No sign of leaks at cylinder or sump
7. Cylinder inspection superficial scan all around it looks good.

Ideas from the brainiacs?
THanks
 
Inspect the Distribution Spider

My buddy had a similar symptom but it moved around from time to time to different cylinders. After hours of agonizing troubleshooting he found a few small pieces of material floating around in the Distributor.
Worth a shot.
 
Fuel Distribution

Check the fuel distribution of the flow divider by doing the bottle check. If you don't know how to do this give me a call.

Don
 
Need ideas for troublshooting.
IO-540, AFP.

Symptom,
Below 1500 RPM, #2 cylinder drops cold. Misses, no EGT, CHT drops.
~1500rpm, cylinder comes back alive, but is running ~100degF egt hotter than normal/others. Leaning it shows the cylinder continues to lean and peaks early indicating cylinder is lean. Mag checks good.

Bring RPM up higher ~2000rpm and the cylinder functions normally. EGT in line with others. Mag checks function as expected.

Actions so far.
1. Compression check hot and cold GOOD. 78/90
2. Swap injectors, swap injector lines around. Problem stays with the one cylinder. (I though for sure plugged injector.
3. Rockers snug, nothing unusual under rocker cover.
4. Oil change, filter clean.
5. Plugs look good.
6. Intake tube tight. No sign of leaks at cylinder or sump
7. Cylinder inspection superficial scan all around it looks good.

Ideas from the brainiacs?
THanks

We saw this exact thing on an angle valve IO360. It was the #3 cylinder. It turned out to be the #2 cylinder intake. The o-ring on the intake tube was letting in air. How this affected the #3 cylinder, who knows. repaired the tube, problem gone.
 
Sounds like an induction leak on number two cylinder intake system. Classic intake/ induction leak symptoms! Double check the pipes especially if the lip under the flange is cracked and also that the non used 1/8 pipe plug in the cylinder intake port.
When the suction is high, in that cylinder?s intake system, as it gets as you go to lower RPM and power, something is killing that cylinder. Either you are sucking in outside air or you are getting more fuel then you should have. Maybe a partially restricted FI nozzle vent that allows more fuel at high suction??
Good Luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
I also am leaning towards an intake leak. Your right. Classicsymptoms.
Ill check the tube and npt port.

Ill check it and report back.
 
Check the fuel distribution of the flow divider by doing the bottle check. If you don't know how to do this give me a call.

Don

I figured that since I hooked up the line to a different port off the flow divider, that would be ruled out.

I do have my test jars though. Easy enough to try.
 
For crying out loud Mike, you've got 6 cylinders! Most of us make do with just 4!:D
No sympathy!:rolleyes:

Mutha
 
I know this is a relatively old post, but I found it last night after looking for hints to solve the same problem (gotta love this forum). Almost ready to fly this thing but I can't get it to idle smoothly.

RV-9A, IO-320 from Aero Sport Power, zero time, Lightspeed Plasma II on right, Slick mag on left, Precision EX-5VA1 servo. Below approximately 1,000 rpm, #3 cyl CHT/EGT drop way off. Other cylinders appear fine. Above 1,000 rpm, all cylinders are fairly balanced (actually EGT on #3 goes slightly higher than the other three, CHT stays lowest, but not ridiculously out of balance). At idle, it does feel like one cyl isn't firing, pretty rough.

I originally thought this was simply a matter of adjusting the idle mixture and idle screw on the servo, but I wasn't getting anywhere with that after several tries. Once I noticed the temps on #3 cyl were consistently low, I thought I fouled the plugs, so I pulled and cleaned them, but they weren't necessarily dirty. Same problem after cleaning the plugs. After more testing and studying, I started thinking the fuel spider was "unbalanced" and #3 cyl wasn't firing below 1,000 rpm for whatever reason. But after finding this post, I was thinking "maybe air leak" or plugged injector.

Today I found the injector on #3 cyl loose (too loose). So I removed them all, then tightened everything, including the fittings at the spider. All injectors and fittings appeared clean. After finding the loose injector on #3 cyl, I thought maybe I found the problem. But after firing the engine, still had the same rough idle and cold #3 cyl.

FWIW, the test data recorded by Aero Sport Power and sent with the engine appears consistent with what I'm seeing (manifold pressure & fuel flow at 650, 1,200 and 1,500 rpm appear close to what was documented). I have an AFS EFIS for engine instruments.

Is it possible the engine RPM is reading higher than actual and I'm try to set the idle too low? Probably not likely. RPM input to the EFIS is from the Slick mag.

Turning a Whirlwind 200RV CS prop. I've been told that my idle rpm needs to be set a little higher (850 minimum) because of the lightweight prop and less mass turning up front. But I can't get down to 850 without losing a cylinder and rough idle.

Probably should mention that this engine sat for probably 8 years hanging on the front of the plane and in a hangar while life mostly got in the way of building. Back at it now. The engine fired right up on the first start about a month ago, but never idled smoothly, so I've been trying to figure out what not quite right since then, along with addressing other minor issues prior to a first flight.

Any thoughts, suggestions or advice before I tear into the air intake system on a brand new engine?

As always, any advise is always appreciated.
 
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Any thoughts, suggestions or advice before I tear into the air intake system on a brand new engine?

With the fuel off, and the ignitions off, remove the top plug from the cylinder in question and pull the propeller through a couple of turns -- can you find TDC and feel the suction? (Verify the valves are opening/closing as intended)

From there, I would eliminate variables one at a time.

1. Ignition systems (LSE first, then mag) -- does it idle on LSE only, mag only?
2. Check fuel delivery - do the shot glass flow test under each injector, are they even?
3. How about swapping injectors around -- does the issue follow the injector?
4. Verify that there is a restrictor (insert) in the injector.
5. Make sure the "A" hole (<grin>) is in the right place on the injector body -- see Lycoming SI-1275-C, Step #6

As an aside, I had a bad injector on my new-out-of-the-factory Lyc. YIO-360-A1B6; it can happen.
 
Hey, Brian. Thanks for the quick response.

I haven't checked idle on just the mag or LSE. I certainly can. The mag check (on both sides seems fine at 1,700 rpm. With LSE only, rpm drop is just under 100 rpm. With mag only, rpm drop is just under 200.

FWIW, a good friend with virtually the same plane says he shows zero rpm drop with LSE only during mag check. This that what should be normal?

Not sure what a 'shot glass' test is. Am I just measuring the flow through each injector (and timing it?) to ensure the flow is equal?

I can certainly swap injectors to see if it follows the injector or stays with Cyl #3.

I didn't see any restrictor in any of the injectors - I can see right through all 4 of them with a flashlight.

Not sure how the A needs to be aligned on the injector, but I'll look at the Lycoming publication you suggest. I did notice an A on each injector. I figured it just identified each injector as an A injector (identifying orifice size, or something like that).
 
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Hey, Brian. Thanks for the quick response.

I haven't checked idle on just the mag or LSE. I certainly can. The mag check (on both sides seems fine at 1,700 rpm. With LSE only, rpm drop is just under 100 rpm. With mag only, rpm drop is just under 200.

FWIW, a good from with virtually the same plane says he shows zero rpm drop with LSE only during mag check. This that what should be normal?

Not sure what a 'shot glass' test is. Am I just measuring the flow through each injector (and timing it?) to ensure the flow is equal?

I can certainly swap injectors to see if it follows the injector or stays with Cyl #3.

I didn't see any restrictor in any of the injectors - I can see right through all 4 of them with a flashlight.

Not sure how the A needs to be aligned on the injector, but I'll look at the Lycoming publication you suggest. I did notice an A on each injector. I figured it just identified each injector as an A injector (identifying orifice size, or something like that).

Your typical "mag check" will/should yield a ~100 RPM drop from [BOTH] to L or R. With an LSE it should be something like 2000 RPM (BOTH), 1990 (LSE Only), 1850 - 1900 (Mag Only). Said differently, the spark & advance of the LSE gets the mixture burning sooner so there isn't any real RPM drop from [BOTH] -- more of a sound difference in my experience.

Re: shot glass test - yes, put a shot glass under each injector and turn the boost pump on -- see what the result is after 30 seconds, 1 minute..

Definitely have a look at the service instruction, there is a detailed parts explosion of all the various injectors used by the Lyc. IO. (figure 2, typical for a normally aspirated Lyc.)
 
One more thing to look at is the temperatures during the mag check -- how do the CHT/EGT's behave on the LSE only, Mag only?
 
OK, here's an update. I swapped injectors between Cyl 3 and 1, made sure everything was tight, and followed the installation of the injectors (orientation) such that the "A" is pointing down. Fired the engine up and all looks much better. Still idling a little rough, but all cylinders are firing - all temps pretty even across the board, not perfect, but not bad.

Now I think it's just a matter of idle adjustment and idle fuel flow to ensure all is reliable.

Thanks for the help and suggestions, Brian.
 
I know this is a relatively old post, but I found it last night after looking for hints to solve the same problem (gotta love this forum). Almost ready to fly this thing but I can't get it to idle smoothly.

RV-9A, IO-320 from Aero Sport Power, zero time, Lightspeed Plasma II on right, Slick mag on left, Precision EX-5VA1 servo. Below approximately 1,000 rpm, #3 cyl CHT/EGT drop way off. Other cylinders appear fine. Above 1,000 rpm, all cylinders are fairly balanced (actually EGT on #3 goes slightly higher than the other three, CHT stays lowest, but not ridiculously out of balance). At idle, it does feel like one cyl isn't firing, pretty rough.

I originally thought this was simply a matter of adjusting the idle mixture and idle screw on the servo, but I wasn't getting anywhere with that after several tries. Once I noticed the temps on #3 cyl were consistently low, I thought I fouled the plugs, so I pulled and cleaned them, but they weren't necessarily dirty. Same problem after cleaning the plugs. After more testing and studying, I started thinking the fuel spider was "unbalanced" and #3 cyl wasn't firing below 1,000 rpm for whatever reason. But after finding this post, I was thinking "maybe air leak" or plugged injector.

Today I found the injector on #3 cyl loose (too loose). So I removed them all, then tightened everything, including the fittings at the spider. All injectors and fittings appeared clean. After finding the loose injector on #3 cyl, I thought maybe I found the problem. But after firing the engine, still had the same rough idle and cold #3 cyl.

FWIW, the test data recorded by Aero Sport Power and sent with the engine appears consistent with what I'm seeing (manifold pressure & fuel flow at 650, 1,200 and 1,500 rpm appear close to what was documented). I have an AFS EFIS for engine instruments.

Is it possible the engine RPM is reading higher than actual and I'm try to set the idle too low? Probably not likely. RPM input to the EFIS is from the Slick mag.

Turning a Whirlwind 200RV CS prop. I've been told that my idle rpm needs to be set a little higher (850 minimum) because of the lightweight prop and less mass turning up front. But I can't get down to 850 without losing a cylinder and rough idle.

Probably should mention that this engine sat for probably 8 years hanging on the front of the plane and in a hangar while life mostly got in the way of building. Back at it now. The engine fired right up on the first start about a month ago, but never idled smoothly, so I've been trying to figure out what not quite right since then, along with addressing other minor issues prior to a first flight.

Any thoughts, suggestions or advice before I tear into the air intake system on a brand new engine?

As always, any advise is always appreciated.

Many think the spiders purpose is a 4 way diverter, but in reality its primary purpose is to restrict flow at idle. Beyond idle, balancing is done via injector sizing. There is a V shaped slot for each of the 4 lines and a piston that rides up and down to open and close this slot. At idle, the piston is at the bottom of the V to restrict fuel flow. If you have a piece of debris (usually from manufacturing work) in the bottom of the #3 V slot, that cylinder will be starved of fuel at idle, yet above 1000-1200 or so will run just fine, as the piston is opening the larger part of the V and the tiny blockage at the bottom is inconsequential.

Take apart the spider and clean out the slots. Note that there is a spring just under the cover, so use caution that it doesn't disappear in your shop as you take the cover off.

Larry
 
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with it sitting that long, take a look at the intake gaskets and hoses. There's a good chance they need replacing. Leaking ones will affect a smooth idle quite a bit.

Vic
 
Yes, I am afraid of that ....... I looked at them without taking anything apart, and all seems OK, but probably impossible to ascertain the integrity of those parts with disassembly and inspection.

Right now, all appears fine after swapping injectors between two cylinders and installing all injectors properly ('A' pointing down, per the Lycoming bulletin).

I know the proper thing to do would be to replace the intake gaskets and hoses now. I have already replaced the oil filter (before putting oil in it for the first time) as well as the fuel tank drain o-rings.
 
You really can't tell by looking at them, unless you see the telltale blue stain from the fuel.
A quick test, if you have a 4-cylinder EGT gauge, is to pull power back to idle while on base leg or final. Watch the EGT's. They should all go DOWN. If any or all of them increase, you have intake leaks.

Vic
 
Good advice, thanks! And no 'blue stain' that I can see. Haven't flown the plane yet, Wednesday is supposed to be the first flight.
 
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You really can't tell by looking at them, unless you see the telltale blue stain from the fuel.
A quick test, if you have a 4-cylinder EGT gauge, is to pull power back to idle while on base leg or final. Watch the EGT's. They should all go DOWN. If any or all of them increase, you have intake leaks.

Vic

Another clue you have an induction leak is "backfiring" (technically after fire caused by a ridiculously lean mixture that's still burning when the exhaust valve opens -- also causes the EGT to rise) when you close the throttle ("Pop-pop-poppity-pop-pop...")
 
Vic, where would I typically see the 'blue stain'? I see a little on top of the filtered airbox around the servo flange, after I've run the engine for a bit. It actually looks more like blue oil, very light, and not much of it. Is that a sign of an intake air leak? Or should I only be concerned if the blue stain is seen coming from the intake hoses or intake gaskets for any of the cylinders? No sign of anything blue at those two locations.

Thank you for your assistance on this.
 
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