Ignition System: Description and Operation

PURPOSE
To produce a spark that will ignite the air/fuel mixture within an engine's cylinders, ignition systems generate high voltage and direct it to spark plugs at each cylinder. Voltage must be high enough to jump the spark plug gap under compression and it must be supplied at the correct time under a wide range of operating conditions.

DESCRIPTION
This vehicle uses an ECU controlled electronic ignition system. Components include:

1. Ignition coils.
2. Cam and crank angle sensors.
3. Ignitor (power transistor).
4. Platinum tipped spark plugs.

CRANK/CAM ANGLE SENSORS
The crank/cam angle sensors provide the ECU with signals regarding engine rpm and #1 cylinder TDC (camshaft position). Together with other inputs, the ECU calculates ignition timing over the range of vehicle operating conditions. For additional information on these sensors, refer to COMPUTERS AND CONTROL SYSTEMS.

IGNITOR
An ECU controlled power transistor is used as a switch to regulate current flow through the coil primary circuit. Each time current flow is interrupted, high voltage is induced to fire the spark plugs. Except for the initial setting, timing is determined by the ECU.

SECONDARY IGNITION COMPONENTS
Individual ignition coils are mounted directly above the spark plugs. This eliminates the need for plug wires and a distributor. Platinum tipped spark plugs are used. They provide a longer service period than non-platinum type.