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On my way to Oshkosh this year, during my descent to Green Lake me engine started to run very rough. Out of instinct I flipped on the fuel pump, went full mixture and just did a quick mag check. After a few very long seconds the engine recovered and continued to run normally. This was a little concerning to say the least! I looked at my engine monitor and noticed the #4 EGT dropped to near zero.  Here is a zoomed in image of the engine graph. This is one feature I really like about the GRT EFIS that the other EFIS manufacturers do not have - real time historical graphing of engine temperatures. Sure, the other manufacturers offer data logging for analysis, but that doesn't offer you any piece of mind when you are in the air! I can't seem to find the color mapping key on the internet now, but I did find right after the event occurred the green line was the temperature of the #2 cylinder. All of the EGT temperatures dropped when I enriched the mixture, and then when #2 recovered on it's own, I leaned the engine back out again.  I knew I most likely needed to at the very least clean out the exhaust valve guide for #2, so I dropped the exhaust.  Exhaust valve for #2 as seen through the exhaust port.  I removed the exhaust springs and the valve was certainly a little tight in the guide. More concerning than the tightness of the valve in the guide was the valve tended to get "stuck" in the closed position relatively easily with a good pull. Even more concerning was when I added air to the cylinder via the compression tester, a lot of air was leaking past the exhaust valve. When I say a lot, I mean I could feel it on my fingers below the exhaust flange. This was clearly more than a sticky exhaust valve.  Not knowing if I needed to pull the cylinder for this fix, I found the manual for my engine with the part number and serial numbers of my cylinders. I could get the cylinder sent out for $800-ish according to my A&P friend, or buy a brand new cylinder from Superior for $1495. It's relatively the same amount of effort for either option, so I might as well put a new jug on for double the price. I still have more investigation to do to the underlying cause - I just wanted to have all the information possible to make a decision if needed. 
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Last Modified: October 5, 2024 |