Ignition System Operation
In a conventional ignition system, the ignition coil produces a high voltage current and the distributor then relays this current, at the required time, to each spark plug. In the distributorless ignition system, two sensors, the camshaft position sensor and the crankshaft position sensor, tell the Engine Control Module (ECM) which cylinder is ready to fire. The ECM then sends an ignition signal to an electronic ignition coil. This ignition coil then produces and sends a high voltage current to the proper spark plug. Distributorless ignition is a "wasted-spark" system in which two spark plugs fire simultaneously. One cylinder fires at TDC on the compression stroke, while the other fires at TDC of the exhaust stroke.
The cylinders are grouped together by firing order. For example, firing order is 1-3-4-2. Cylinders 1 and 4 are in the same position, while cylinders 2 and 3 are 180 behind. Plugs 1 and 4 fire together, as do the plugs in cylinders 2 and 3.
This means that an ignition spark is fired in one cylinder while at the same time a "waste" spark is fired in the companion cylinder.
Because of dual plug firing, if an inductive tachometer is connected to a plug wire, it will indicate an engine RPM that is twice the actual speed (i.e., 1,600 RPM, instead of 800 RPM).