Search the Community

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

During runup I noticed the mag drop to be at 200RPM on the left side. After leaning the engine at higher RPM and allowing it to run for about a minute, the drop remains between 100-125RPM. Most people I spoke to suggested that I might have had fouled plugs so I replaced them all with Tempest UREM38E (massives). After running up with new plugs, the RPM drop was normal but the engine ran rough on the same side (left). I also noticed that when full throttle is applied the RPM does not go any higher than 2500-2600. Has anyone experienced this before that might be able to shed some light as to what might be going on?