Troubleshooting ignition with JPI engine monitor data.

[cnoe]

This is a follow-up to an earlier post titled "Ignition Wire Boot"

I wanted to share a few graphics demonstrating a minor issue I discovered in the ignition system in my IO360. There have been no symptoms affecting functionality or performance but in studying my JPI downloads post-flight I found this issue.

Ground run-ups are fairly normal with only a minor rpm drop between right and left mags. More importantly I see normal EGT rise and fall on the engine monitor during ground run-up. (see below)

But LOP mag checks at altitude are a better way to check mag performance so I occasionally perform this check in flight. I will lean to well LOP and then switch to the right mag for 30 seconds, both for 30 seconds, and then left mag for 30 seconds checking for excessive engine roughness and normal EGT rise. All seemed well enough during these tests and I did not notice any unusual temps. But when I uploaded the profiles to Savvy's website an obvious anomaly stood out where the #4 EGT would rise excessively on the left mag reaching a temperature about 100 F. higher than when running on the right mag (close to 1,650 F.). (see below)

This certainly appeared to be an ignition problem but my dual-mag had less than 100 hours on it since the 500-hour service, and since the problem only appeared on cylinder #4 I didn't believe it to be the mag itself. So I pulled the plugs which I cleaned, gapped, and rotated. It's surprising how the lower plugs collect a lot of lead fouling, even though I lean aggressively on the ground. I am now trying to delay enrichment on descent until at least on final, but I digress... While the plugs were out I took pics of the exhaust valves just to be sure there was no leakage due to a burned valve (all was good there). (see #4 exh. valve below)

So now I figured it had to be related to a weak spark on #4 between the left mag and the lower #4 plug. The ignition wire became the primary suspect and then I recalled an earlier issue where the plug boot (insulator) was damaged while replacing the plugs a while back. When I pulled the wire off lower #4 again there was no obvious arcing but the boot definitely had a small chunk out of it near the tip where the contact-spring is located. FYI, Champion recommends lubricating their boots lightly with either Dow Corning 4 or 111 (I'd been previously told NOT to do this). Now to verify the problem all we had to do was swap the lower and upper ignition leads on #4 and repeat the LOP mag check. As expected everything seemed normal except the excessive rise in #4's EGT now occurred on the right mag instead of the left. This was again confirmed after downloading the newest JPI data and graphing. (see below)

The problem followed the wire, and the insulator-boot has an obvious defect. Even though the spark is acceptable in all normal operating conditions, the added stress of running on one mag allows a portion of the energy to escape past the damaged insulator/boot into the spark plug body and to ground. So now I'm getting a new replacement boot and contact-spring and will report back with the post-repair results when able.

Thank you to my local mechanic and the Mooneyspace crowd for helping me find the problem and the parts to remedy it.

Cnoe

[carusoam]

cnoe,

Again, great detailed logic and graphics.

Questions:

1) What altitude did you collect your data at?

2) How deep LOP were you able to go?

From My IO550 experience, at lower altitudes, I can run down to about 90°F LOP before the engine quietly ceases to run.

I am wondering with the damaged boot, how deep LOP you would get before it started becoming an obvious issue.

Thank you again.

Best regards,

-a-

 

[cnoe]

Last LOP mag check was at 8,500'. I believe the previous was at 6,500' several days prior.

It ran comfortably at 45/52 F. LOP but ran out of juice around 65/77 F. LOP. GAMI has been great in helping me get tuned in lately as I previously had trouble getting beyond 30 F. LOP. It takes an amateur like myself significant tweaking to dial in a 4 cylinder to run deeply LOP, but it's a fun challenge.

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