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PSA: Check the P-lead on Lycoming mags before you pull the whole mag
Had a 172 with a rough running O-320 last Thursday and I was about to pull the left mag to send it out for overhaul, which would have been a $700 rebuild and a week of downtime. Turned out the P-lead nut on the mag was loose enough to arc and it was shorting out every few seconds. Took me 10 minutes with a 3/8 wrench instead of a week in the shop. Anyone else catch a mag issue that was really just a loose connection on the ignition side?
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gibson.wesley22d ago
That "loose enough to arc and it was shorting out every few seconds" detail is the part most guys skip past when they're chasing a rough mag. A P-lead that grounds out now and then is a lot sneakier than a dead mag, since the engine will run fine on the ground check and only act up under vibration in the air. I check the nut torque and the wire condition at every oil change now, because it is cheap insurance against pulling a mag that was never broken.
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