201er Posted June 20, 2016 Report Posted June 20, 2016 Noticed an unusually hot EGT in cruise lately. Been trying to figure it out a while. Recently did an in-flight mag check. On one mag the rise is normal but on the other, this specific cylinder rises way more than usual. It was 1600 and still climbing when I went back to both. This explains the high EGT in cruise cause it averaged out the good and bad plug. What can cause an EGT to be hotter on just one mag on just one cylinder? Quote
takair Posted June 20, 2016 Report Posted June 20, 2016 I would start with the spark plug. You can swap them top to bottom. Next would be harness and then magneto. Probably weak spark on that plug. 1 Quote
201er Posted June 20, 2016 Author Report Posted June 20, 2016 1 hour ago, takair said: I would start with the spark plug. You can swap them top to bottom. Next would be harness and then magneto. Probably weak spark on that plug. Why would weak spark lead to higher EGT? Delayed burn? Quote
MB65E Posted June 20, 2016 Report Posted June 20, 2016 Hi! Correct. Sounds like a failing plug. However, I'd pull the injector on the hot cylinder. I have had clogged injectors do strange things. It's shocking on how little debris it takes to have an issue. good luck! -Matt Quote
ArtVandelay Posted June 20, 2016 Report Posted June 20, 2016 1 hour ago, takair said: I would start with the spark plug. You can swap them top to bottom. Next would be harness and then magneto. Probably weak spark on that plug. Why would weak spark lead to higher EGT? Delayed burn? Yes, same reason 1 mag causes higher EGTs Quote
ArtVandelay Posted June 20, 2016 Report Posted June 20, 2016 Hi! Correct. Sounds like a failing plug. However, I'd pull the injector on the hot cylinder. I have had clogged injectors do strange things. It's shocking on how little debris it takes to have an issue. good luck! -Matt I would not... I would do one thing at a time, pulling injectors when not needed may introduce another maintenance induced problem. Quote
takair Posted June 20, 2016 Report Posted June 20, 2016 Yes, you still have combustion going on in the exhaust stack.... Quote
nels Posted June 20, 2016 Report Posted June 20, 2016 I had the same problem. It was evidently a weak spark on one plug. Right after taking off and while in the pattern I noticed the same high exhaust temp but relatively cool cylinder. I returned to the ground and pulled and cleaned both plugs. I started aggressively leaning the mixture immediately after start up and never had the problem again. Quote
201er Posted June 20, 2016 Author Report Posted June 20, 2016 3 hours ago, nels said: I had the same problem. It was evidently a weak spark on one plug. Right after taking off and while in the pattern I noticed the same high exhaust temp but relatively cool cylinder. I returned to the ground and pulled and cleaned both plugs. I started aggressively leaning the mixture immediately after start up and never had the problem again. It's not a fouled plug. It's not injectors, had them cleaned since the problem started and made zero difference. It's not the timing cause I had it checked. Must be a bad plug. Do you replace just the one? Quote
ArtVandelay Posted June 20, 2016 Report Posted June 20, 2016 3 hours ago, nels said: I had the same problem. It was evidently a weak spark on one plug. Right after taking off and while in the pattern I noticed the same high exhaust temp but relatively cool cylinder. I returned to the ground and pulled and cleaned both plugs. I started aggressively leaning the mixture immediately after start up and never had the problem again. It's not a fouled plug. It's not injectors, had them cleaned since the problem started and made zero difference. It's not the timing cause I had it checked. Must be a bad plug. Do you replace just the one? If they are Champions, I would replace them all with Tempest. Quote
201er Posted June 20, 2016 Author Report Posted June 20, 2016 Just now, teejayevans said: If they are Champions, I would replace them all with Tempest. They are Champions. Came with the factory reman. So running them till they need replacement for fine wires. Number 3 right mag, is that top or bottom? Quote
MB65E Posted June 20, 2016 Report Posted June 20, 2016 How many hours on the plugs? Football shaped electrodes yet? If you replaced them all you wouldn't know which one was bad. Trace the wires back from the mag harness. It's hard to varify online with out a diagram. That Bendix switch can be confusing. Here are some diagrams out of the Lycoming OH manual. For what it's worth, I really like the Tempest plugs, but wouldn't change them all as long as you can prove they test well. The cost of the fine wires is too steep for me at the moment. You do seem to fly a lot, and would appreciate their reliability. -Matt Quote
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