Plug? Ignition harness? Mag?

[Ratherbflying]

I think I've got at least two different problems here. But I'm spinning on this and I need the communities help.

Culprit(s)?

[carusoam]

Give us a hint...or three...

often the issue is in flight...

sometimes it is during run-up...

you have given 10 seconds of data.  And the axis is labeled rpm...  Top graph looks like CHT, bottom EGT.

what are you showing here?  We're there any symptoms that were happening at the same time, or just funky data?

EGT#3 (yellow line) looks like it has stopped giving real data.  Pull, clean, look for damage...

reseat and check again.  Check the wire all the way back to the instrument.  It may be loose at a connection.

What else are you seeing?

Best regards,

-a-

[kortopates]

There is no validity in comparing the two peaks between Left & Right mags. What we actually do is look at the Odds as a group and the Evens as a group, since then we are looking only at tops on one mag and bottoms on the other mag. If the Odds Tops match the Evens Tops with the Odds Bottoms matching the Evens Bottom - then we know the mag are timed together or not split timed.  The EGT rise  comparison is between Both and Left and Both and Right. For that we are looking for a 50-75 EGT rise or more.

But your data is too short to be useful. It looks like we only got 3 data points in each position before changing it.  We want to see at least 10 data points on each position to allow temps to stabilize so with a 6 sec data sampling rate you want to use a full minute on Left, Both and Right which totals 3 minutes. Do this LOP after a Gami spread or since carbureted get it as lean as you can without any roughness - i.e. enrich just enough to be smooth. 

More details here on how to do the test as well as how to interpret it: https://www.savvyanalysis.com/articles/in-flight-diagnostics 

Or you can always click on the button to request analysis.

Edited March 15, 2016 by kortopates

[Ratherbflying]

8 hours ago, carusoam said:

sometimes it is during run-up...

Bingo! I was hoping the 1700 in the RPM scale would give away the run-up. The issue is a 45 rpm difference in mag drop, very close to the maximum allowable drop, and is high for this engine. Historically, the mag drops have been very even.

Other hints... Five hours out of annual. Tempest fine wires in the bottom plug positions and Champions on top. Mags had their 500 hour inspections last year.

Cylinder 3 EGT may have stopped giving data, but this happens every time I do a run up, so I'm thinking more likely that spark on the lower plug is weak or missing.

7 hours ago, kortopates said:

Or you can always click on the button to request analysis.

Hi Paul! The inflight mag check is the same as the three others I've submitted to you over the past year, plus the plane just went in to the shop to have the prop governor pulled and sent out for inspection. To do that they had to pull the right mag so I'm trying to decide if I should send it out for inspection. They are testing the harness today, and they are moving the number 3 cylinder tempest plug to the number 1 cylinder to see if the problem moves. But it'll be a while before the thing is back together and I can check that. 

Oh, and my data interval is still set to 2 seconds.

[kortopates]

6 hours ago, Ratherbflying said:

Hi Paul! The inflight mag check is the same as the three others I've submitted to you over the past year, plus the plane just went in to the shop to have the prop governor pulled and sent out for inspection. To do that they had to pull the right mag so I'm trying to decide if I should send it out for inspection. They are testing the harness today, and they are moving the number 3 cylinder tempest plug to the number 1 cylinder to see if the problem moves. But it'll be a while before the thing is back together and I can check that. 

Oh, and my data interval is still set to 2 seconds.

Hi Steve,

I don't know how many hours you have on that mag but based on what I've seen in the past I would take advantage of having it off to get it opened up and inspected and at least re-timed internally. Your unpressurized mags should go 5 yrs/500hrs without servicing, but beyond that they should be inspected. Frankly if both mags were near the 5yr/500hr I'd do them both. (I pull my pressurized mags annually because they are much more prone to internal corrosion from moisture being pumped in.)

With a 2 sec data sampling rate, which is great, you should do 30 sec's per key position. That gives 15 data points but we also need time to see temps stabilize. 10 seconds is just not enough time. Even though 30 sec may not show much improvement, the added time is important to show any possible misfire.

Its normal that you will see less of a rise going from the Bottom plug of cylinder to the Top plug of the cylinder. The bottom plugs generally give a higher rise because combustion on the bottom only plug is not as thorough as combustion on the top plug which is generally cleaner, free of oil etc. As a result, combustion is slowed on the bottom plug only and as the exhaust valve opens up the EGT probe is seeing the incomplete combustion continuing as it the gas is exiting resulting in a higher EGT rise. So a drop in EGT rises from bottoms to tops is normal. But what is not is seeing less than a minimum rise of 50-75F rise on each plug when operated on a single mag. We measure that from the both position to the single mag rise. 

Edited March 15, 2016 by kortopates