Ignition Coil
Coils come in four tower, six tower vertical connector, and six tower horizontal connector models. Two adjacent coil towers share a common coil and are called a matched pair. For six-tower coil (six cylinder) applications the matched pairs are 1 and 5, 2 and 6, and 3 and 4. For four tower coil (four cylinder) applications the matched pairs are 1 and 4, and 2 and 3. When the coil is fired by the powertrain control module (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.