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EGT Fluctuation

Kupde

Active Member
Patron
Just changed out the fuel restrictions on cyl#3 and #4 on my RV-10 from an 0.028 to a 0.027. Test flight shows a very brief EGT drop(3 to 5 seconds) while going through the leaning operation on cylinder #3 only. Cylinder #3 drops about 200 degrees below the others(1200F vs 1400F) for the 3 to 5 seconds and then recovers with no further fluctuations. This repeats anytime going back through a leaning operation at different altitudes and engine settings. Never seen this before- anyone have any thoughts?

Kevin
RV-10
 
Very interested in the replies you get on this. I'll be balancing my injectors soon as I progress through phase 1.

My EGT on one cyl scrolled quickly downward and back up again shortly before the Dynon-supplied probe in question went T.U. for good, and had to be replaced at about 5 hours TT.
 
Sounds like #3 is running too lean. Can you upload the data to Savvy and share a link?
 
Just changed out the fuel restrictions on cyl#3 and #4 on my RV-10 from an 0.028 to a 0.027. Test flight shows a very brief EGT drop(3 to 5 seconds) while going through the leaning operation on cylinder #3 only. Cylinder #3 drops about 200 degrees below the others(1200F vs 1400F) for the 3 to 5 seconds and then recovers with no further fluctuations. This repeats anytime going back through a leaning operation at different altitudes and engine settings. Never seen this before- anyone have any thoughts?

Kevin
RV-10

I would be very suspicious of that EGT probe/wiring. I had a similar pre-failure signature on one of my ALCOR EGT probes very early on (~50 hours).

Swap the probe, see if the signature follows the probe -- if so, replace the probe.

Usually, issues with fuel injectors resolve themselves VERY quickly -- like a stumble that the EIS doesn't even see, or they don't resolve at all -- total blockage.
 
I would be very suspicious of that EGT probe/wiring. I had a similar pre-failure signature on one of my ALCOR EGT probes very early on (~50 hours).

Swap the probe, see if the signature follows the probe -- if so, replace the probe.

Usually, issues with fuel injectors resolve themselves VERY quickly -- like a stumble that the EIS doesn't even see, or they don't resolve at all -- total blockage.

+1

Sounds more like an indication problem than a fuel delivery problem. Pretty hard to have a fuel issue that can cause an EGT to drop then regain 200* in 3 seconds.

Larry
 
https://apps.savvyaviation.com/flights/4730142/86ffcb46-1bde-45ff-a053-b3c28bb00ca0

Not sure if you can get to the data with the link above? Also, no change in CHT and I'll do as suggested with the EGT probe.

Thanks

Kevin
RV-10

Thanks for the link. Definitely a probe connection issue, as mentioned above. GAMI spread is pretty good with #2 trending leaner.

Time: 00:14:28-00:14:54
EGT2 peaked at 12.2
EGT3 peaked at 12
EGT1 peaked at 11.8
EGT4 peaked at 11.8
EGT5 peaked at 11.8
EGT6 peaked at 11.8
GAMI spread is 0.4
 
I love data...

You can definitely see something going on there --

EGT on #3 drops out frequently, 9:08, 16:20, 19:29, and so on, regardless of fuel flow settings.
 
Another oddity...

Keep an eye on the #2 CHT.

Note 11:41 to 14:32 and 21:08 to 26:41 -- #2 CHT is NOT following the normal distribution or rate of change.

This tells me the #2 Cylinder is burning too hot / too fast as the fuel flow increases (richer:faster, leaner:slower), change to a smaller orifice (e.g. .027" from .028") and see if that curve flattens out.
 
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Thought I would thank folks who had commented on this one. I found the smoking gun which was small chafe in the insulation between the 2 thermocouple wires. The red wire wore through where it was rubbing against the opposing wire nut. I guess best practice would be to insulate all the T/c connections before attaching the final sleeve. I’ve tried to attach a picture but not sure how well the attachment will come through.

Thanks

Kevin
 

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I would place the lock washer under the nut. It looks like the washer is under the screw head...
 
A star washer should be fitted between the ring terminals as a first course of action as per instructions for this type of connection.
 
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