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Thread: IO-320 leaning issue, help wanted

  1. #1
    Zac Weidner's Avatar
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    Default IO-320 leaning issue, help wanted

    Hey everyone,

    We installed an engine monitor on our Twin Comanche this winter, and I've been learning all sorts of little things about our engines since then. It's been very enlightening for some issues we had and didn't realize it. I think we've solved and corrected most of them (nothing major), but there's one that's puzzling us still. The right engine #2 cylinder has a strange thing going on during leaning that keeps it from running smooth LOP. I know many are not for the whole LOP idea, but we're planning to only run there when <65% power, because it'll save a good deal of fuel. The left engine does great there, and the cylinders are looking great inside with a borescope. The culprit cylinder on the right engine, however, is still puzzling me and I'm out of ideas at this point without trying GAMI injectors.

    The reason I'm not sure GAMI's would even help, is because there seems to be a "double peak" of the EGT on that cylinder when leaning. The other cylinders all have a nice smooth peak as looked at on a graph, but this #2 cylinder has a not-so-gentle looking double peak on both sides of the others, and then falls off and basically quits running altogether. The attached graph is a good representation of what I'm seeing. I've tried playing musical injectors with them in every combination, but no luck getting rid of this issue. I even tried one older style injector which we had on the shelf from upgrading ~12 years ago.


    I'd appreciate any ideas or guidance as to who I could contact that might be well-versed in this sort of issue.

    Attachment 124082017-09-02 (2).jpg
    Last edited by Zac Weidner; 09-02-2017 at 07:41 PM.

  2. #2
    andya's Avatar
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    Default Re: IO-320 leaning issue, help wanted

    If you swapped injectors around, then probably not the problem and I assume you've cleaned the injectors recently.
    Highly unusual to get a double peak when heading for lean of peak. May be something not correct in the "spider" distribution
    unit on top. Might remove the line to that cylinder and blow it out to be sure something is not in there blocking the line.
    Always possible indication error, if lead wiring was long enough, I would switch the #2 and $4 egt leads to see if it follows the
    lead or now shows the problem in the #4 display. You had talked about getting overhaul, is this an overhauled engine, cylinder or
    are we still running same as before engines. If he same old cylinders, I wonder if there is some anomaly in that cylinder causing this.

    I do not run lean of peak and only have egt on #3 and #4 on both engines I don't know where #1 and #2 are as I lean but I have leaned to
    slightly lean of peak below 70 percent or so (guessing) but have never had any roughness or missing (have only taken to 10-20 lean of peak for
    less than 20 second or so.

    something else that might cause the roughness would be a spark plug problem.
    usually if you loose spark the egt will go high as all the fuel doesn't finish burning til in the exhaust pipe.
    I could see spark or the plug causing the roughness on that cylinder but that doesn't explain the valley after the first peak.

    sorry for the rambling, just throwing thoughts out
    "Progress is our most important problem"

  3. #3
    Zac Weidner's Avatar
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    Default Re: IO-320 leaning issue, help wanted

    This is on the older engine, at around 2,000 smoh and 1,200 since new cylinders. I believe the probes are reading correctly based on the vibration levels during leaning. The left engine (recently overhauled) leans until it quits with no roughness. I removed the intake pipe and replaced the hose and gasket with no change in performance afterwards. I've also done an aggressive mag check, meaning with a very lean mixture and have seen no issues there. I also removed the top from the flow divider and blew out the lines. Perhaps I should measure how far the valves are opening vs. the other cylinders.


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    Last edited by Zac Weidner; 09-03-2017 at 09:08 AM.

  4. #4

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    Default Re: IO-320 leaning issue, help wanted

    The double peak usually means that cylinder is running lean. A lean cylinder will have an EGT that rises before the others when you start to lean the mixture (because it started out leaner than the others). And so the EGT peaks before the others. And the second peak occurs when you keep leaning enough to start having misfires in that cylinder. With a misfire the fuel all goes through unburnt to the exhaust where the pipe is hot enough to ignite the fuel. The burning of additional fuel in the exhaust pipe is what gives the second peak.

    Since you've already swapped nozzles and cleaned the flow divider, I'd check for a intake leak next.

    Tim

  5. #5
    Zac Weidner's Avatar
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    Default Re: IO-320 leaning issue, help wanted

    Quote Originally Posted by bluejeepdad View Post
    The double peak usually means that cylinder is running lean. A lean cylinder will have an EGT that rises before the others when you start to lean the mixture (because it started out leaner than the others). And so the EGT peaks before the others. And the second peak occurs when you keep leaning enough to start having misfires in that cylinder. With a misfire the fuel all goes through unburnt to the exhaust where the pipe is hot enough to ignite the fuel. The burning of additional fuel in the exhaust pipe is what gives the second peak.

    Since you've already swapped nozzles and cleaned the flow divider, I'd check for a intake leak next.

    Tim
    Before a short test yesterday, I removed the intake pipe and replaced the hose and gasket with no change in performance. I'm thinking I'll do a test in cups with the injectors and lines without injectors to see how even the flows are cylinder to cylinder. Perhaps all the nozzles I've tried just happen to be exactly the same flow and I need one substantially larger to provide more flow to that cylinder.

  6. #6
    Zac Weidner's Avatar
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    Default IO-320 leaning issue, help wanted

    Here are the representative fuel flows without and with injectors attached to the lines, respectively. These seem to directly correlate to what I see on the EGT's when leaning. How closely should a flow divider meter between cylinders?


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    rocket's Avatar
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    Default Re: IO-320 leaning issue, help wanted

    Just a thought. Can you do the flow volume check at the same fuel pressure/GPH as your 65% LOP setting? It possible a fuel flow difference might be more pronounced at that setting?

    also don't discount the plug swap mentioned up thread.

    rocket

  8. #8
    andya's Avatar
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    Default Re: IO-320 leaning issue, help wanted

    I test mine lines like that every time I clean nozzles and mine come out pretty even , much like your 1,3,4
    "Progress is our most important problem"

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    Default Re: IO-320 leaning issue, help wanted

    Quote Originally Posted by Zac Weidner View Post
    How closely should a flow divider meter between cylinders?
    Zac, sorry I missed where you said you already replaced the intake gasket and hose.

    The second flow test without the nozzles might not be 100% representative. Without the pressure drop across the nozzles the servo (fuel injector) will reduce the fuel pressure to maintain the flow rate. But the flow divider responds to the lower pressure by moving its plunger lower in the bore. These flow dividers have more variation at low plunger settings than they do at wide open. So the flow divider might not be quite as bad as it seems.

    But on the other hand the first and second tests both have a similar pattern so that is pointing to the flow divider. If you can, it would be interesting to rerun the first test with nozzles 1 and 2 and their hard lines swapped. If the low flow doesn't follow nozzle/line 2 then that confirms a flow divider problem.

    Tim

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    Zac Weidner's Avatar
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    Default Re: IO-320 leaning issue, help wanted

    Quote Originally Posted by andya View Post
    I test mine lines like that every time I clean nozzles and mine come out pretty even , much like your 1,3,4
    What sort of cups do you use? I always hate how much I have to spring the lines to get a little cup under the ends. I try to never flex those lines if possible.

    I'm thinking about swapping the #2 injector lines between left and right engine and flying again. That would probably be the easiest way for me to accomplish the same thing.


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