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Matt,
To be helpfull, we'd all need more info on your engine,prop, mixture setting when the engine roughness started. Sounds like a plug problem, or a EGT probe/wire problem perhaps..??? Not knowing more than your post I wonder why you choose to run way over squared, MP vs RPM..??? The engine garus will probably despute this, but I don't run that far from MP/RPM squared, at any condition (climb,cruise,or descent) say 2300RPM & from 21 to 25" MP, and ALL power changes are made slowly...My 320 Lyc seems to purr more often.. 650 hrs on a 0-320, compression on all four was 78/80 last week.. Regards Don Skeele A&P
From: "Matt Hapgood" <matt.hapgood@alumni.duke.edu>
Date: 2005/06/01 Wed AM 11:47:03 EDT
To: "Lancair Mailing List" <lml@lancaironline.net>
Subject: [LML] misfire
I had a problem on a flight on Saturday that I have never had before. The plane is just out of annual. I made a one hour flight at 25" x 2400 RPM. Approach asked me to descend relatively quickly. I pulled the power back to about 21" x 2500 RPM and the engine started running rough. I noticed the #4 EGT at zero. I pushed the MP back up and it cleared up. I pulled the RPM down to about 2300 - 2400 and it cleared up. Just leaning the mixture didn't solve the problem, nor did richening the mixture.
This was the first annual where I have NOT replaced the plugs. Instead, an A&P just cleaned them (they are automotive Iridium plugs).
I have electronic ignition and electronic injection. Was it a clogged injector? Not likely, as it cleared up at higher MPs and lower RPMs. Was it a spark problem? Not impossible, but it would have had to kill both plugs. Were the plugs fouled? Not impossible, as #4 is my richest cylinder. But the problem happened later when I tested it, after I had been running for 20 minutes LOP.
Unfortunately, I tried to get it to happen again on the ground and, of course, it won't repeat itself (at about 20" and 2400 RPM).
Any thoughts? I'm going out to decowl the plane and inspect the plugs, but I'd appreciate any thoughts as to what to look for.
Matt
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