Matt
said: 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, I don't think it is a bad plug since
it is easier to fire a plug at 21 MAP than it is at 25 MAP. If you have
run the engine at this exact MAP/RPM before without a problem, then I would look
for a sensor or connection that was disturbed during the annual. If
this is a newly tested/run MAP/RPM then I would check the MAP tables for the
EFI. It sounds like the computer was commanding the engine to not run. Why, I
don't really have a good idea. What is puzzling is just one cylinder being
affected. I assume it idles OK. ??? If so then the EFI injectors are most
likely OK.
Craig Berland