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Lightspeed plasma coil erosion

FORANE

FORANE

Well Known Member
On my last flight I noticed what seemed like an occasional slight misfire. The engine monitor appeared normal except for cylinder #2 running higher than typical EGT. The EGT on that cylinder would drift up a few times during the flight. I could reliably cause it to come back down by slightly enriching the mixture. I was running lean of peak at 9000 MSL. I was tempted to do a mag check but chose not to due to solid IMC with low layers.

So, what would cause high EGT on one cylinder? CHT on that cylinder remained normal. I considered it may be due to running lean. Maybe an induction leak? Maybe a clogged injector? Maybe a failing spark plug?

I pulled the wires off the Lightspeed coils and found this on the number 2 cylinder coil pin.
IMG20260530153342.jpg

The other coil also exhibited some erosion on the number 3 pin.
IMG20260530153405.jpg
I'm guessing this started as corrosion, led to increase in resistance, heat and finally erosion of the pin. Has anyone seen this before on a coil? Should I be using dielectric grease on the boot connections?
 
Last edited:
Check the cables for proper resistance, and check while bending the cable on both ends. And check the coil for proper resistance. I've had a dual LS Plasma 2+ system for 18 years now, and the only time I've seen discoloration is when the cable had high/infinite resistance. I've never used dielectric grease.

And then replace your coil mounting bolts with the proper length, and installed in the proper direction (heads on top, nuts with washers below).
 
hgerhardt said:
Check the cables for proper resistance, and check while bending the cable on both ends. And check the coil for proper resistance. I've had a dual LS Plasma 2+ system for 18 years now, and the only time I've seen discoloration is when the cable had high/infinite resistance. I've never used dielectric grease.

And then replace your coil mounting bolts with the proper length, and installed in the proper direction (heads on top, nuts with washers below).
Click to expand...
…and proper nuts (read: MS21042)
 
hgerhardt said:
Check the cables for proper resistance, and check while bending the cable on both ends. And check the coil for proper resistance. I've had a dual LS Plasma 2+ system for 18 years now, and the only time I've seen discoloration is when the cable had high/infinite resistance. I've never used dielectric grease.

And then replace your coil mounting bolts with the proper length, and installed in the proper direction (heads on top, nuts with washers below).
Click to expand...
Yeah, I checked resistance today. 8,000 ohms across both coils and the proper 50 ohms per foot on all cables was present.

Good catch on the attachment hardware. Ha, I didn't even notice that. Wasn't my install...
 
When running on one plug, egt will rise around 150*. Your terminal shows signs of arcing, so no surprise that you are getting occasional egt spikes. I heves seen this with my msd wires, but at the spark plug side . Used pliers to squeeze down the terminal a bit and problem disappeared.
 
FORANE said:
On my last flight I noticed what seemed like an occasional slight misfire. The engine monitor appeared normal except for cylinder #2 running higher than typical EGT. The EGT on that cylinder would drift up a few times during the flight. I could reliably cause it to come back down by slightly enriching the mixture. I was running lean of peak at 9000 MSL. I was tempted to do a mag check but chose not to due to solid IMC with low layers.

So, what would cause high EGT on one cylinder? CHT on that cylinder remained normal. I considered it may be due to running lean. Maybe an induction leak? Maybe a clogged injector? Maybe a failing spark plug?

I pulled the wires off the Lightspeed coils and found this on the number 2 cylinder coil pin.
View attachment 119125

The other coil also exhibited some erosion on the number 3 pin.
View attachment 119126
I'm guessing this started as corrosion, led to increase in resistance, heat and finally erosion of the pin. Has anyone seen this before on a coil? Should I be using dielectric grease on the boot connections?
Click to expand...
When you clean the corrosion off the pins, reconnect the plug wires and go fly please report back if that fixed your issue.
 
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