Interpreting JPI data.

[Lood]

I've flown my new engine for about 16 hours SMOH and since day one I've been slightly annoyed by the #4 cylinder running a bit hotter than the other 3. Although I've noticed it on the JPI during flight, I downloaded the data yesterday and it is confirmed that the same #4 cylinders' EGT runs cooler than the other 3.
The temperature difference is not really a train smash, but unfortunately my nature is such that it bothers me - all the time.

On average, the #4 cylinders' CHT runs about 25-30 deg hotter than the rest and ITO EGT, about 40 deg colder. This must indicate something? If the EGT on this cylinder was in line with the others, I would attribute the higher CHT to an improper sealing baffle maybe, but the fact that the EGT is also out of line should indicate that something on cylinder #4 is different. Could it be a bad spark plug or maybe something to do with the injector?

I would appreciate your expert advice.

[danb35]

Absolute values of EGT are all but meaningless, so the fact that EGT #4 is cooler than the other cylinders doesn't tell us anything of value.  For that matter, a CHT that's 25-30 degrees hotter than the others isn't particularly significant either, but those numbers are more meaningful than EGTs.

On EGTs, you're really interested in two things: where the cylinder peaks compared to the other cylinders, and what the temperature is compared to normal for that cylinder.  The first tells you how rich or lean the cylinder is compared to others (and will give an indication of induction or injector problems); the second tells you if there's an ignition problem in that cylinder.  If you had a bad spark plug, your EGT should be about 150 degrees higher than normal.

[DonMuncy]

Mike Busch of Savvy Aviator is the most knowledgeable person I know in interpreting JPI info. He may murder us if we start bombarding him with requests, but I found him to be very accommodating and glad to help. I sent him the readouts from one or two of my flights and he responded quickly. He does not want the graph, but the raw data to read.

[Lood]

Thanks for the replies. Seeing that I had new injectors installed, I'll repeat the Gami lean test this coming weekend to see what the spread is now and apart from that, I'll know which cylinder runs where. I'm also ready to go LOP. Been reading up on it and spoke to quite few people the last couple of days and I feel confident to try it out.