Coil Pack
Coil packs come in 4-tower, Series 5 4-tower, 6-tower horizontal connector and Series 5 6-tower models. Two adjacent coil towers share a common coil and are called a matched pair. For 6-tower coil pack (6 cylinder) applications the matched pairs are 1 and 5, 2 and 6, and 3 and 4. For 4-tower coil pack (4 cylinder) applications the matched pairs are 1 and 4, and 2 and 3.
When the coil is fired by the PCM, spark is delivered through the matched pair towers to their respective spark plugs. The spark plugs are fired simultaneously and are paired so that as one fires on the compression stroke, the other spark plug fires on the exhaust stroke. The next time the coil is fired the situation is reversed. The next pair of spark plugs fire according to the engine firing order.