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High / Erratic EGT on Cylinder #4 (IO 320)

jj13

jj13

Active Member
I need help on this one. This started about 2 months ago. My number 4 Cylinder's EGT started ruining about 150 deg. higher lean of peek than normal in an oscillating manner. See data chart.

What I've done;
Replace EGT prob
Replaced both spark plugs
Replaced both ign wires
Switch injector with Cylinder #2

The engine runs perfectly smooth. Max speed has not changed.
Climb out is normal for all 4 EGT temperatures. This only happens lean of peek.

But at startup the #4 EGT is about half (500 deg) vs (1000 deg) on the other three. At runup #4 catches up with the other three.

Any help would be greatly appreciated.

Thank you

N1354J EGT N4 Issue.jpg
 
I'm not an expert on engine by any means, but I can reference what Mike Busch recommends in his books. I believe this information is also in several online articles and videos as well. There are a handful of tests that can be done to narrow down what to look at:
- Ignition Stress Test (in-flight LOP mag check)
- Mixture Distribution Test (GAMI lean test)
- Induction Leak Test

Mike also has a "SavvyAnalysis Flight Test Profile" that's outlined on his website. Some of it duplicates the first three tests referenced.

I'll be interested in what you find, so please keep us posted.
 
I would verify that #4 really is #4. I chased a problem on a friends plane for months, only to discover that the original builder had the probes the wrong spots.. I had to de-pin the EMS plug and put them in the right spots. Turned out, the problem probe was in a neighboring cylinder.
 
Oscillating EGT in one cylinder can also be a potentially sticking exhaust valve indicating lead buildup in the valve guide or other causes. Take that with a grain of salt. Since you used SAVVY AVIATION’s tool, you can ask Mike’s team to analyze the data for you. He has quite a few videos on YouTube about EGT troubleshooting as well for what it’s worth. I am not a mechanic by the way.
 
I’d spend $15+/- and change the connectors to Omegas. This would rule out connectors being the cause now and in the future. If it persists then go for the more difficult and costly solutions.
 
Sorry, but the Savvy plot was not much help w/o other corroborating variables.

But since you are injected, and if the +150F is consistent then it could be:

1. lower flow nozzle - run a leaning test to track peak of each cylinders temp. If #4 peaks earlier, then possible it is a little lower in flow. Plot peaks vs FF to get FF offsets.

2. Ignition - if #1 shows the GAMI spread to be low and #4 is not an outlier then one plug or wire is misfiring. You have apparently checked this so seems to be eliminated, but verify you have correct EGT matched to a known physical cylinder.

I missed the ignition type, if a mag - -has it been internal inspected for the SB's - like the wobbling rotor conductor?

3. Sticky exhaust valve - if #1&2 are cleared, then this could be something to check. Hard to do a running check, but removing the VC/rockers and spring to check tightness of the valve-in-guide. i.e. wobble test.

If it was a leaking intake, the GAMI test will help sort that too. If one cylinder is leaner then it can have an intermittent misfiring plug just because of the lean limit. I have observed that. A leaking intake would be more of an issue at part throttle. After sorting standard altitude cruise GAMI spread, then a low altitude slower speed could reveal the contrast of a leaking intake.

Good luck.
 
Last edited:
chromedome said:
EGT's need a good ground, try cleaning the area under the clamp

Reggie
RV-14a
RV-12
Click to expand...

Not all EGTs use grounding.. I believe the Advanced are the only ones that ground, I don’t believe the Dynon ones care about the ground..
 
Any "K TYPE" thermocouple will work with Dynon equipment. Dynon supports both grounded and ungrounded probes. This info from Dynonsupport.

best
Reggie

RV-12
RV-14A
 
Issue Found

I really felt I eliminated any ignition issues so I didn't give that info. I have two Lightspeed Engineering Plasma II. I though all the coils were good since each one supports two cylinders, and the issue was only showing up on #4. Also in cruse when I turned off each side the EGT increased on all cylinders. Out of desperation I finally switched the leads on each of the two coils that are shared between 3 and 4. To my surprise the problem move to Cylinder #3. I determined it was the coil that supported the bottom plugs for #3 and #4. I then replaced it. It's now all back to normal.

It appears that one of the connections to the bottom coil was partially internment. This only showed up in cruse lean of peek, rich of peek EGTs were all good.

I want to thank everyone for their very good feedback that I'm sure I'll be able to use in the future.

Thank you
 
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