P-Mag Ignition Wiring

I just installed a set of P-Mags on my Lycoming O-235 and need an answer before I start building the ignition plug harness. I was told once that one mag should fire the upper plugs on one side and the lower plugs on the other side. What is the reason for this configuration verses firing the top front and the bottom rear, or just have one mag fire the top and the other mag fire the bottom plugs??? I am searching for a good reason, because now I dont see why any configuration mentioned above has any advantage over another. I would appreciate it if someone could give a clear explanation to me and others why one method is preferred over the others.


Thanks,
Mike Shook
RV9a
942WG

Mag wiring

Left P-Mag,-Top left plugs.....Bottom right

Right P-Mag,-Top right plugs...Bottom left

I belive it can done other ways, but that is the way I was taught.

Old vs. New

The old way is one "mag" does the top on one side and the bottom on another. This way when you check the mags you aren't thrown off by fouling on the bottom plugs. With real mags that wear out, this is the better and standard way.

Some of us with dual pmags have chosen to wire them so one fires all the top plugs and the other all the bottom plugs. This way if the bottom plugs start to foul you get an RPM drop on that pmag. This "new" way is a better way to get a read on your plug fouling, which I think is reasonable given that pmags seem to work or not, rather than wear out.

Hans

Good Explanation

Hans, I like your explanation and it makes sense to me, so thats exactly how I built both harnesses, right pmag is upper and left pmag is bottom plugs.

Thanks,

Mike Shook
RV9a
942WG

Dual EI plug wiring

I have my four LSE coils mounted on top of the engine with them in line with the cylinders and on either side of the centerline. I order to have all of the plug leads the same 23" length to balance out resistance and capacitance, I ran the lead from the coil that is closest to the cylinder to its bottom plug on that side, and the other lead to the top plug on the other side. I guess that would make it like the mag wiring. Klaus usually says to make one EI fire all of the top plugs and the other to fire all of the bottom plugs.

nucleus said:

The old way is one "mag" does the top on one side and the bottom on another. This way when you check the mags you aren't thrown off by fouling on the bottom plugs. With real mags that wear out, this is the better and standard way.
...
Hans

Click to expand...

Or...

You could buy an EICommander and have it tell you when your plugs are fouled.

I wired mine the old, one P-mag firing the top plug on one side and the bottom on the other.