Ignition System: Description and Operation

Direct Ignition System:

PURPOSE
The high tension ignition system must be able to deliver sufficient energy to ignite the air/fuel mixture under all conditions. If sufficient ignition energy is not available, ignition does not occur and the resultant combustion miss produces reduced power and unacceptable tail pipe emissions.

Direct Ignition Component Locations:

CONSTRUCTION
The "motionless" or direct ignition system consists of:
^ Digital Motor Electronic (DME) control unit
^ Six individual coils
^ Secondary resistors
^ Spark plugs

Electrical Diagram:

OPERATION
The primary side of the coils are connected with the positive battery terminal via the ignition switch. During the primary current-flow time (coil saturation) the coils are connected to ground through the power output transistors of the DME control unit. Based upon load conditions received by the DME control unit in relation to various engine speeds a three dimensional ignition performance characteristic "Basic Ignition Map" is used to optimize the ignition to achieve the most favorable exhaust gas and fuel consumption performance for any given load or speed condition.

Ignition Timing Program Map:

When the throttle valve is in the closed position, the bottom line of the basic ignition map is selected as the idle/coast characteristic. For engine speeds below the nominal values, the ignition timing is advanced to obtain idle stabilization. For coasting ignition timing is programmed to obtain minimum exhaust gas pollutants and optimum driveability performance. For the wide open throttle position, the top line of the basic ignition map is selected. This full-load characteristic is programmed with engine knock limits taken into consideration. For very high ambient temperatures the ignition is retarded as a function of engine and intake air temperature.

Refer to Computers and Control Systems for more information.