On a waste-spark system, two plugs, 180 apart in the firing order, fire in series; one just before the top of the exhaust stroke, and one near the top of the compression stroke. So for all practical purposes, they fire simultaneously! On the Lycomings, it's 1&2, 3&4, and 5&6 on the 6 cyl. So if cylinder 1 is normal and 2 is not, for instance, it would indicate possible breakdown in the #2 wiring, a fouled plug, or bad connections, as Scotty pointed out. The coil transformer secondary is totally isolated from ground. The voltage leaves one terminal, jumps a plug gap, travels across the engine, jumps the other gap, then returns to the other coil terminal. It's a good idea to keep the high-voltage wiring mounted away from any metal, as there is capacitive coupling from the coil to ground. This coupling, along with capacitive coupling from the HV wiring to ground, can form a capacitive voltage divider which reduces the output. Excess wiring capacitance, acting in shunt with the secondary resistance, can create a voltage drop which reduces peak voltage and slows rise time. On my Lancair, I use non-metallic standoffs where possible to keep the HV wires away from the engine. It doesn't have to be a lot; 1/2" works. It's also prudent to keep HV wiring from closely parallelling other wires so as not to induce voltage transients in them; they may be part of sensitive circuitry. These considerations apply to all waste-spark systems, not just LSE!