Each coil is connected in series between spark plugs of companion cylinders. For every engine cycle (720' of crankshaft rotation), ignition is carried out twice at each coil, both spark plugs firing simultaneously. One plug fires before TDC on the compression stroke while the companion fires at the same position before TDC on the exhaust stroke. This type of secondary distribution is referred to as waste spark.
The three ignition coils are mounted on the top of the engine to the upper section of the head cover. As you face the engine, the coil for the 1-6 cylinder pair is on your left. The coil in the center serves the 3-4 cylinder pair, and the coil to the right serves cylinder pair 2-5.
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