Engine Anomaly

In reviewing my Emax files I found an anomaly on a flight last month. I have my theory as to what happened, but I thought I’d turn it over to the collective wisdom.
Here is the graph from Emax (courtesy of Tony Glazer’s fantastic analysis tool):
The big anomaly is the dropout of the CHT of cylinder #5, marked as “B” on the graph. The background is I was cruising LOP-go-far mode from Cheyenne, WY to Palwaukee, IL. From 10:22 to 10:27am you can see where I was nudging the mixture a bit leaner (EGT’s getting cooler) to get the FuelRemaining to climb back to my comfort zone.
If anyone would like to treat this as a quiz, you can stop reading at this paragraph. I have a theory, but its only a guess and I’ll give it below. If anyone really wants to dig in, the full EMax datafile is attached.

My guess is I had a partially blocked fuel injector on cylinder #5. The clue for me is marked “A” on the graph, where the EGT for cyl5 drops and EGT’s for the rest rise. I interpret that as reduced fuel flow into #5, and the resultant rise in pressure provides more fuel for the remaining cylinders, thus enrichening their mixtures and increasing EGT. The leaning of cyl#5 caused its mixture to burn more slowly which means the gasses were hotter when the exhaust valve opened so the Exhaust gas was hotter. But the less fuel burning later means there was less heat transfer to the cylinder, and the CHT dropped.

I eventually became concerned by the low CHT (MEMO TO SELF–NEED BETTER SCAN SINCE IT TOOK AROUND 10 MINUTES!) and performed a high-power lean mag check (point “C”). I had a bad check on one side, a good check on the other and a good check on a repeat of the first side. Here is the mag check data enlarged:

The question I can’t answer in this theory is why the mag-check cleared the problem.

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Thank you,
The COPA Team
1-56497-Engine_070103_084135_out.log (375 KB)