Does this look like a bad pmag coil?

[rv8ch]

This is from a recent in-flight mag test. I was flying slowly, taking full advantage of a nice tailwind by putting along at about 7400' density altitude, 20" MAP, and 7.3 GPH, 2400 RPM, 148 KTAS.

The hump on the left is when the right mag was running, and the hump on the right is for the left mag. I get a much higher EGT on cylinders 3 and 4 which indicates to me the fuel burn is not as efficient as in the other two cylinders when running on just this pmag. I guess it could be two weaker spark plugs, or two spark plug wires that are not working as well, or the coils - I believe that a single coil serve 1&2 and the other coil 3&4 - but I might be wrong. Happy to get your views before I attack it with tools this weekend.

 

[Rdog420]

Temperature excursions in paired cylinders (1&2 or 3&4)a) Observe while running on both Left and Right ignitions. i) Slight EGTs rise and slight CHTs drop on one cylinder pair. Note which pair has the temperature shift. Proceed to b).b) Observe while briefly switching between Left (alone) then Right (alone).i) EGTs and CHTs will crash, along with very rough engine on the faulty side. c) On the faulty ignition, confirm the three wires at the green coil plug are secure. Give each wire a gentle tug with needle nose pliers next to the plug. Resecure any lose wires. If none are found return ignition to E-MAG for repair. Problem is not field serviceable.

https://emagair.com/wp-content/uploads/2023/12/Manual-114-L_C4-V33.pdf

 

[wirejock]

Temperature excursions in paired cylinders (1&2 or 3&4)a) Observe while running on both Left and Right ignitions. i) Slight EGTs rise and slight CHTs drop on one cylinder pair. Note which pair has the temperature shift. Proceed to b).b) Observe while briefly switching between Left (alone) then Right (alone).i) EGTs and CHTs will crash, along with very rough engine on the faulty side. c) On the faulty ignition, confirm the three wires at the green coil plug are secure. Give each wire a gentle tug with needle nose pliers next to the plug. Resecure any lose wires. If none are found return ignition to E-MAG for repair. Problem is not field serviceable.

https://emagair.com/wp-content/uploads/2023/12/Manual-114-L_C4-V33.pdf

I don't want to drift, but have a similar p-mag question. I've read the manual several times and still not clear if I have a problem. Mine are wired top/bottom. When I shut down either left or right, I see an rpm drop. Next time I'll note exactly how much. It's enough where I wouldn't want to fly on one mag.
I don't see any change when power is interrupted. Just when one mag is shut down (p-lead grounded). Is this normal?
I've heard others tell me the engine runs normally on either mag so I'm wondering.
I do see the section in the manual where it mentions troubleshooting by CHT/EGT temps so I will also log better data next time.

 

[lr172]

I don't want to drift, but have a similar p-mag question. I've read the manual several times and still not clear if I have a problem. Mine are wired top/bottom. When I shut down either left or right, I see an rpm drop. Next time I'll note exactly how much. It's enough where I wouldn't want to fly on one mag.
I don't see any change when power is interrupted. Just when one mag is shut down (p-lead grounded). Is this normal?
I've heard others tell me the engine runs normally on either mag so I'm wondering.
I do see the section in the manual where it mentions troubleshooting by CHT/EGT temps so I will also log better data next time.

Ignition advance is a combo of both. So when you shut one off (kill the sparking, not changing the input power source), it has the effect of retarding total ignition advance. The result is a rise in egt and slight reduction of rpm. In cruise, each pmag is quite advanced and therefore the effect is somewhat less, as the advance of just one is enough to run near optimum. The effect is greater on mags that don’t advance and therefore running on one is NOT close to optimum.

 

[lr172]

View attachment 111634

This is from a recent in-flight mag test. I was flying slowly, taking full advantage of a nice tailwind by putting along at about 7400' density altitude, 20" MAP, and 7.3 GPH, 2400 RPM, 148 KTAS.

The hump on the left is when the right mag was running, and the hump on the right is for the left mag. I get a much higher EGT on cylinders 3 and 4 which indicates to me the fuel burn is not as efficient as in the other two cylinders when running on just this pmag. I guess it could be two weaker spark plugs, or two spark plug wires that are not working as well, or the coils - I believe that a single coil serve 1&2 and the other coil 3&4 - but I might be wrong. Happy to get your views before I attack it with tools this weekend.

Something is definitely going on with the coil, wire, or plugs for the #3&4 on the left pmag. Spark came much later on that coil (timing retarded). However, the coil is contolled by the sw and executed by an igniter. Either of those could also be an issue. I don’t see wires or plugs doing this, probably not the coil either. They tend to fire or not and can also be weak. However, none of those usually result in a late spark. Weak coils more typically create intermittent misfires.