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IO 540 one EGT spiking

GaryK

Well Known Member
Friend
I?ve had this happen 3 times now. Level in cruise and all of a sudden #4 EGT starts to climb. In all cases I enriched the mixture, fuel pump on for 30 seconds or so and after all EGT?s cool down lean the mixture and things go back to normal. I did noticed a slight stumble in the engine but nothing big. After this happened a had an engine start that that seemed to be stuck valves. Most likely unrelated but #5 and 6 were cold. Decided to check all the valve guides with an A@P friend. Most were pretty hard to move so we decided to ream all of them. 3 hours and we were done. #4 was one of the ones that seemed pretty tough to move. Took a short test flight and all seemed normal. Took a nice 6 hour round trip at 8000 and 9000 feet and had the same thing happen on #4, EGT started spiking up. It didn?t help switching ignition, have a mag on the bottom and LS on top plugs. I had already checked the injector and didn?t see anything. The EGT probes were changed 2 years ago. Any suggestions would be appreciated.

I was going to swap injectors for the heck of it and then maybe swap EGT probes.

IO 540
700 hours
Injectors are NOT GAMI
Dynon HDX and engine monitor

Didn?t notice and change in CHT but didn?t let it go on for long before enriching.

Thanks
Gary
 
Savvy analysis

Hi Gary,

Do you subscribe to savvy analysis? Following my engine issues I found the free service invaluable when it came to diagnosing exactly what was going on second by second.

Did you check the inlet valves too?

If the exhaust valves were all tight you may have carbon build up within the cylinder too. Potentially pre- ignition of the fuel/air charge prior to the spark plug firing. Pre-ignition caused by some other ignition source such as an overheated spark plug tip, carbon deposits in the combustion chamber and, rarely, a burned exhaust valve; all act as a glow plug to ignite the charge.
 
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Simon,
I don?t subscribe but have started looking into Savvy. We did check the inlet valves and also all clearances.

Thanks
 
Be ware

I pop the flash drive into the back of the skyview after each flight lately and upload it to savvy right away. You can spend hours looking at all your parameters, very useful.

Following my valve reaming adventure I went through each second of the next flight analysing EGT’s/RPM’s/FF. Really helped my confidence in the engine and procedure.

Best of luck figuring it out, I’ve just gone through exhaust valve issues and couldn’t relax until I had it resolved.

Simon
 
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Check the plugs too. I find that if one plug is not firing, the EGT climbs significantly. Perhaps one of the plugs is firing intermittently.
 
Sound s like #4 has a plug that is intermittently not firing. When one of the plugs stops firing, the EGT will rise. When it starts firing again, the EGT drops back to previous.

Larry
 
I checked the plugs but its an easy test to just change them both.

Thanks for the comments.
 
I checked the plugs but its an easy test to just change them both.

Thanks for the comments.

It could also be the ignition wire. Check the resistance of both wires. It could also be the cap inside the mag if you have one of those.

Larry
 
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