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Low EGT and CHT, one cylinder, high power

Michael Burbidge

Well Known Member
I recently installed an JPI EMD-740 engine monitor. It is revealing some interesting information.

On my first two flights I'm noticing that my #4 cylinder EGT and CHT drop off under high power scenarios.

And when I climb to altitude (9500 ft.) both the EGT and CHT steadily decline on the #4. #2 exhibits the same behavior but not so drastically.

This is an O-320. I would like to figure out what is going on here. Do you have suggestions on the first things to check?

Here's a look at the logs. I've annotated it with a description of what was going on during the flight. Here's the link to savvyanalysis.com if you want a closer look: https://savvyanalysis.com/flight/2537164/4b9c6423-cbf7-46db-a30f-e838ff4acb72

Without the engine monitor I have not noticed anything unusual about the engine, in terms of sounds and vibration.

m4bh5Aa.jpg
 
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Ditto

My O-360 A1A 180 hp engine fitted with an Ellison TBI does exactly the same thing. I've been searching for a solution for a while now and trying multiple different air straighteners and air box modifications, but the issue remains. Number one and three are higher EGT and CHT than two and four. Four will steadily drop during extended climbs. At lower throttle openings things even out better. Additionally, while descending, things are very even. Appears to be related mostly to throttle position, but also angle of attack. Could be fuel pooling out of suspension at the back of the intake system in the oil sump, turbulating inlet air, or a combination.

I suspect there's a large power loss during climb because of the differences between cylinders. Also makes leaning difficult and operating lean of peak particularly so. Easy to run one and three lean of peak while two and four are rich of peak, but I don't like to do this. To get all four LOP, I need the throttle position back, regardless of power output due to altitude.

If yours is doing the same thing with a carburetor, then I suspect the mixture distribution through the heated intake tubes running through the oil sump. I wonder if a cold air induction manifold would do the same thing? I love the easy starting that the Ellison provides and the inverted capability, but would like to up the power and efficiency at high throttle openings.
 
Agree on cylinder to cylinder distribution.

Since you don't notice performance, and it progresses with the climb, I would guess those cylinders are getting really rich. Being a carb, you might just close the throttle a touch and see what changes. I don't find a lot of MAP change at altitude with a little throttle closure.
 
Hi Michael,

I came across this old thread of yours and was wondering if you found a solution?

I have an 0-320 as well and have been experiencing the exact same problems with cyl.#4 on climb-out--steadily decreasing EGT and CHT's.

If I reduce the throttle slightly (as one of your repliers suggest), both temps move back up. If I go back to WOT, the temps drop again.

At cruise, #4 is fine and both temps are in line with the other cylinders.

Any ideas?

Thanks...Peter Millard
 
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