Ignition System: Description and Operation

DESCRIPTION AND OPERATION
The Multiport Fuel Injection System consists of sensors which detect the engine conditions, the POWERTRAIN CONTROL MODULE (PCM) which controls the system based on signals from these sensors, and actuators which operate under the control of the PCM.

The PCM carries out activities such as fuel injection control, idle air control, and ignition timing control. In addition, the PCM is equipped with several diagnostic test modes which simplify troubleshooting when a problem develops.

IGNITION TIMING CONTROL
The ignition power transistor located in the ignition primary circuit turns ON and OFF to control the primary current flow to the ignition coil. This controls the ignition timing to provide the optimum ignition timing with respect to the engine operating conditions. The ignition timing is determined by the PCM from engine speed, intake air volume, engine coolant temperature, and atmospheric pressure.


This system is provided with three ignition coils (A, B and C) and three ignition power transistors (A, B and C) for the number 1 and number 4 cylinders, number 2 and number 5 cylinders and number 3 and number 6 cylinders respectively. Interruption of the primary current flowing in the primary side of ignition coil A generates a high voltage in the secondary side of ignition coil A. The high voltage thus generated is applied to the spark plugs of number 1 and number 4 cylinders to generate sparks. At the time that the sparks are generated at both spark plugs, if one cylinder is at the compression stroke, the other cylinder is at the exhaust stroke, so that ignition of the compressed air/fuel mixture occurs only for the cylinder which is at the compression stroke.

In the same way, when the primary current flowing in ignition coil B is interrupted, the high voltage thus generated is applied to the spark plugs of number 2 and number 5 cylinders, and when the primary current flowing in ignition coil C is interrupted, the high voltage thus generated is applied to the spark plugs of number 3 and number 6 cylinders.

The engine control module controls the three ignition power transistors (A, B and C) to turn them alternately ON and OFF This causes the primary currents in the ignition coils (A, B and C) to be alternately interrupted and allowed to flow to fire the cylinders in the order 1-2-3-4-5-6.

The engine control unit determines which ignition coil should be controlled by means of the signals from the camshaft position sensor which is incorporated in the camshaft and from the crankshaft position sensor which is incorporated in the crankshaft.

It also detects the crankshaft position in order to provide ignition at the most appropriate timing in response to the engine operation conditions.

When the engine is cold or operated at high altitudes, the ignition timing is slightly advanced to provide optimum performance.