JPI EDM 700 / EGT specialists, please help

[podair]

 

First time I have ever seen an unstable reading on the EGT on one cylinder. New plugs, right out of maintenance. I was flying my usual 10,000ft at about 60-65% power , slightly lop. Cylinder 3 EGT varied up and down about 30-40 degrees which is uncommon. Did an inflight lop mag check and I was getting rough running and a big EGT drop on the left mag, but only for cyl 3 , all other cylinders rock solid. Am I right in concluding I have a duff plug? If it was the mag I would get all cylinders running rough? A stuck valve would be seen on both mags? Can-t be a probe thing because there was clearly rough running.

I was already planning to see a mechanic as soon as I landed but weirdly the problem then disappeared after landing. I did a ground mag check at up to 2200 rpm on the EGT in normalise (sensitive) mode and everything was OK, I was getting stable readings on 3 and normal rise on both mags selected individually. So I continued to my next destination.

I then flew for close to an hour  at 2000 ft, flying slightly lop as well , did an inflight mag check at 50% power, everything OK, no sudden drop with cyl 3. 

Could the problem have cured itself or is it something high altitude related like an induction or ignition harness issue?

 

[danb35]

Quote: podair

Cylinder 3 EGT varied up and down about 30-40 degrees which is uncommon.

[podair]

 

well it looks like it cured itself... no problems on the subsequent flight on Saturday, and today flew with a mechanic up hight, we did all kinds of tests and everything was flawless. Only notable thing was the mechanic who had never flown in the aircraft remarking how well it ran! I then flew back to Spain , usual 10,000 ft at 65% , exactly same settings. EGT on cyl 3 was between 1435 and 1440 for two hours... yes ... only a 5 Fahrenheit range! Did two high altitude lop mag checks, zero issues... oh well... guess I am lucky!

only thing I could not do was a download of the EDM (next week's plan).  I am a miser so did not plump $200 for the UBS box and now regret it! I did not have the laptop I normally download it with, and unable to get an old 90s one with a serial port to run at all, and another one with a USB port did not have the right drivers.... aaarghhh.... why can t this thing just bluetooth to the ipad!

I wonder if the whole thing was created by the inflight lop mag test , maybe I wasnt lean enough and somehow caused some arcing. Also I do not have GAMIs but the engine like a lot of normally aspirated Mooneys it runs very well slightly LOP (up to about 50) with stock injectors, but maybe I leaned a bit far and the rough running created some kind of instability. I normally run at peak / 10 lop ish.