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EGT4 Jitter

During a recent flight, the EGT# temperature jittered, which disappeared on its own later. All CHTs were normal. The plugs are 4 year old Tempest massive. What could cause such jitter and disappear on its own? Thank you!

United States

I would first look at the starwasher between the lugs forming the connection between the probe and the harness. It needs to be between the lugs in order to bite itself into the metal.

EBKT

It’s not just jitter, it’s elevated as well which could point to an exhaust valve issue. Why and how that would have fixed itself I’m not sure ;-) Also I don’t know what probes you have, but my personal experience with JPI probes is that 90% of the “engine issues” I’ve detected with them were probe-related (thankfully actually).

EGTF, LFTF

It does look like a bad connection, but it could also be a probe about to fail which produces the same thing: an open circuit.

The open probe detection circuit traditionally used in thermocouple instruments (a pullup resistor ) will generate a high reading when the probe goes open, and that is what you are getting.

I have changed maybe 5-8 EGT probes over 15 years. The hot gas just eats them. One should probably look at replacing the crappy JPI probes with some better material. The thermocouple is a Type K which is common as muck.

Administrator
Shoreham EGKA, United Kingdom

Yes, they are JPI probes, about 4 years old.

United States

I changed 5 EGT probes in 4 years … probably more than average, but those were all the original ones from 2006, so at one point they simply die. € 110 each in my case…

It could also be a pattern associated with sticking exhaust valve – see Mike Busch video here:

Look at 44:30 where he talks about EGT jitter and shows some pictures. It looks a bit different from yours but it is worth checking. I would also try to swap probes between cylinders to see whether the problem moves or stays. If it moves than it is more likely a bad probe or probe connection. If it stays, it is something wrong with the cylinder.

Last Edited by Pytlak at 18 Oct 08:24
LKHK, Czech Republic

Indeed, it can point to a stuck exhaust valve. Your aircraft is a TB20? This would mean Lycoming where it is a frequent problem.

Don’t forget that the EDM recording is very condensed on the time axis. Electric connection issues would usually cause a high frequency jitter.

Stuck exhaust valves come and go until they won’t go again and you’re in for a forced landing. Been there, done that. Look for the usual signs (morning sickness) and check your valve guides according to Lycoming’s SB.

Very rare on the C cylinders.

Administrator
Shoreham EGKA, United Kingdom

The Lycoming SB also applies to C cylinders. Also I do not know which cylinders and valve guides Lucius’ aircraft has.

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