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  #1  
Old 08-18-2021, 03:43 PM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 697
Default Rough Engine at High Power

Today as I was climbing out my engine seemed to be running rough. It wasn't dramatic, but enough that it got my attention. I was at about 1000 AGL, and still full power when I noticed it. It didn't start then, it's just that my attention had been on takeoff.

It was subtle enough that I had to convince myself that the engine was running rougher than usual.

What finally convinced me was an anomaly in CHT temperatures. My number 4 cylinder always runs colder that the others, but it seemed unusually cool.

I stayed close to the airport and leveled off at about 2500 MSL, and pulled the power back some. When I pulled the power back, the engine seemed to smooth out and the CHT on number 4 gradually climbed while the temp of the other 3 cylinders decreased. This seemed odd to me.

I stayed level at 2500 MSL and after a few minutes went to WOT again. The CHT of 1,2 and 3 climbed, and the CHT of 4 decreased. This definitely doesn't seem normal.

My Engine is a carburated O-320-D3G, one p-mag, one slick.

I don't have much experience with engines, so I'm not sure how to diagnose this. I didn't have the right tools at the hangar to be able to de-cowl and inspect the spark plugs. I will do that tomorrow.

But I'm just wondering if this is normal and what are the possible causes?

Attached is graph of CHT/EGT/MAP. At about 12:10 minutes into the flight is where I was leveled off at 2500 MSL and applied full power. I pulled the power back again at about 13:30, and again applied full power at about 15:18, reduced power again at 17:42.
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Michael Burbidge
Sammamish, WA
RV-14A Wings
RV-9A Flying 390 hours!
Last Donation: December 2020

Last edited by Michael Burbidge : 08-18-2021 at 07:36 PM.
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  #2  
Old 08-18-2021, 04:10 PM
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bjdecker bjdecker is offline
 
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 882
Default

Maybe a floating valve?

https://generalaviationnews.com/2013...ent-roughness/

https://www.lycoming.com/sites/defau...0Condition.pdf
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  #3  
Old 08-18-2021, 05:28 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 298
Default

#1 looks weird to me too.
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  #4  
Old 08-18-2021, 10:19 PM
Rick RV-4 Rick RV-4 is online now
 
Join Date: Aug 2006
Posts: 321
Default Primer?

A very easy thing to check…do you have an old school plunger type of primer? If so make sure it is closed all the way.
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  #5  
Old 08-18-2021, 10:31 PM
SportAvServ SportAvServ is offline
 
Join Date: Jul 2006
Location: Ione, California
Posts: 260
Default

Just a wag, but spark plugs can and do fail under higher pressures, simple and worth a look. Do you know someone that has a spark plug tester?
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  #6  
Old 08-19-2021, 06:22 AM
Michael Burbidge Michael Burbidge is offline
 
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Location: Sammamish, WA
Posts: 697
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I don't have a primer line.

I'm thinking spark plug also. Today I'll get the aviation plug tested and just replace the auto plug.
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  #7  
Old 08-19-2021, 06:35 AM
Tim Lewis Tim Lewis is offline
 
Join Date: Aug 2006
Location: Bristow, VA
Posts: 165
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When you go to full power, #4 EGT is falling while all the others rise. Maybe an induction leak on #4, causing it to go lean?

I'd want to do an in-flight spark plug check, lean sweep, and induction leak check to try to better understand the issue:

https://resources.savvyaviation.com/...t-diagnostics/
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  #8  
Old 08-19-2021, 06:43 AM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
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My understanding is that an induction leak would cause EGT to rise. Both EGT and CHT were falling at full power.

I'll do those inflight tests today.
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  #9  
Old 08-19-2021, 06:49 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by Michael Burbidge View Post
I don't have a primer line.

I'm thinking spark plug also. Today I'll get the aviation plug tested and just replace the auto plug.
If one plug failed, the EGT on that Cyl should rise (~150*) and CHTs drop a bit. If both plugs failed, both would drop like a rock.
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Last edited by lr172 : 08-19-2021 at 06:58 AM.
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  #10  
Old 08-19-2021, 06:50 AM
RV6_OKLA's Avatar
RV6_OKLA RV6_OKLA is offline
 
Join Date: Jan 2005
Location: Yukon Ok
Posts: 113
Default Mag Check

Have you done an inflight mag check? I have dual P-Mags and had a coil issue on one P-Mag that affected one cylinder.

Search for Martin Pauly's youtube video: The in-flight Lean-Of-Peak Magneto Check explained
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