The location of the number one cylinder is important because it is the first cylinder in the engine firing order. The firing order is utilized by the powertrain control module (PCM) to properly sequence the ignition system firing of the spark plugs and opening of the fuel injectors. On V type engines, the bank of cylinders containing cylinder number one is also designated bank 1 for diagnostic purposes.
There are 2 common methods of determining the location of the number one cylinder.
On a V type engine, one cylinder head is slightly forward of the other, toward the front of the engine. Cylinder number one is the forward most cylinder in that bank.
On an inline engine, the number one cylinder is located at the front of the engine, closest to the timing cover.