Engine, Cooling and Exhaust > Engine > Tune-up and Engine performance Checks > Firing bespeak > Component details > Specifications
Firing Order: Specifications
The PCM provides a grounding switch for the coil primary circuit. When the switch is closed, voltage is applied to the coil primary circuit. Thiscreates a magnetic field around the primary coil. The PCM opens the switch1 causing the magnetic field to collapse inducing the high voltage in thesecondary coil windings and firing the spark plug. The spark plugs are paired so that as one spark plug fires on the compression stroke, the other sparkplug fires on the exhaust stroke. The next time the coil is fired the order is reversed. The next pair of spark plugs fire according to the engine firingorder.
Coil packs come in 6-tower, 6-tower horizontal and series 5 6-tower models (Freestar/Monterey/F 150 Heritage 3.9/4.2L). Two adjacent coiltowers 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, and3 and 4. 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 firedsimultaneously 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 isfired, the situation is reversed. The next pair of spark plugs fire according to the engine firing order.