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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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