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As a child conversing with my mentor neighbor about small gas engine problems told me that it was all very simple. "It takes three things to make and engine fire. Fuel, spark and compression.
Check fuel first, then spark then compression (mechanical items) While it might be fuel, that is the easiest solution, the symptoms seem like valve to me. I have experienced partially blocked injectors but not a full blockage and so I do not have that to compare it with. As far as the cylinder EGT peaking early and then falling off; Yes that could point to a partially blocked nozzle but we have no way of knowing if this cylinder normally peaks early, there is only one set of data here. Perhaps if we could go back a bit farther to a previous take off and look at that data we could see if things were similar. If it were my plane, I would clean the injectors, flush the fuel system, fill with 100LL, change the spark plugs, and do the valve wobble check. These items are not expensive nor do they take a lot of time, why not? |
I too find the analyzing that is going on in this thread very enjoyable and most of all educational.
In finding the source of the problem, wether that be a stuck valve or a clogged injector, you have to go a little deeper. If this was a stuck valve problem it can quite easily be duplicated since the stuck valve problems are the result of lead build up in the valve guide and or valve stem. A clogged or partially clogged injector can be the result of dirt in the fuel or other particle, inhibiting fuel delivery. There is documented evidence that severely gummed up fuel lines sometimes shed a flake of varnish and cause a clog in the injector nozzle. This may be more llikely the result of stale mogas than avgas. If this was the case then you will not be able to duplicate the problem until the next flake comes off the injector fuel line. If you have done all the things that Tom describes above and the problem goes away, I would do one more thing, replace the injector lines. Not expensive and then you can slice one open and see what it looks like on the inside. |
Scott, can you full-scale the EIS timeline between 10:41 and 10:45?
If that's a Bendix FI, pull the servo inlet fitting and check the fine screen. |
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Coming home from OSH, I had a erratic EGT reading on #1. We were over Ewstern Montana at 12500 or so and just watched it....then got a stumble. I juggled the mixture a bit and started thinking of "Nearest airport". CHT was always rock solid on all cylinders. An hour later it happened again. I increased fuel flow thinking I was getting a lean condition on that cylinder. Fingers crossed the the remainder of the trip. Next day I did just what Tom described....inspected injectors, flow checked them too. All ok. Replaced the plugs(auto). Checked the wiring to the EGT connectors and then did a compression check. I found nothing....but have not had a stumble since. Mine was different than yours, Scott, but I think the troubleshooting is the same. Do the cheap free stuff first. And even then sometimes it's tough to figure out what is going on. |
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Does speak to interrupted fuel supply, possibly. Unfortunately, based on my experience, the only way to identify the cause may be to keep flying until it recurs. I was never able to duplicate the condition on the ground. The first couple of times it happened to me I was terrified- I flew straight back to the airport (I was always nearby, being in Phase 1 at the time) and landed. And the problem always "cured" itself before I landed. Eventually I realized that the engine wasn't on the verge of rapid inflight-disassembly and I was able to get some additional data. |
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The definition of a cool head may have a different meaning for a pilot that flies upside-down a couple of feet from other aircraft close to the ground than it does for the rest of us (Kahuna). Trouble shooting in flight is called 'flight test' and should be done solo. Whenever anything goes wrong in flight - especially a rough engine in a single engine airplane - the number one measure of success is did you get the airplane on the ground safely without causing harm to people or property? You scored 100% in that regard, Scott...... Congratulations! The method you used to accomplish that goal is not important, the result is. You didn't further tarnish the name of experimental aviation in the eyes of the non-flying public or scare the young lady away. In fact you gave her a good glimpse of how possibly scary circumstances can be handled with success. When you get your problem fixed, I hope she goes up with you again.
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I'm thinking you had a stuck valve... short period IMHO. Fly the plane. :)
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