This ignition system does not use a conventional distributor and coil.
It uses a crankshaft position sensor input to the electronic control module (ECM).
The ECM then determines electronic spark timing (EST) and triggers the direct ignition system ignition coil.
This type of distributorless ignition system uses a ``waste spark'' method of spark distribution.
Each cylinder is paired with the cylinder that is opposite it (1-4 or 2-3).
The spark occurs simultaneously in the cylinder coming up on the compression stroke and in the cylinder coming up on the exhaust stroke.
The cylinder on the exhaust stroke requires very little of the available energy to fire the spark plug.
The remaining energy is available to the spark plug in the cylinder on the compression stroke.
These systems use the EST signal from the ECM to control the electronic spark timing.
The ECM uses the following information:
Engine load (manifold pressure or vacuum).
Atmospheric (barometric) pressure.
Engine temperature.
Intake air temperature.
Crankshaft position.
Engine speed (rpm).
DIRECT IGNITION SYSTEM IGNITION COIL
The direct ignition system (DIS) ignition coil is mounted near the rear of the camshaft carrier on the single overhead camshaft engine.
On the dual overhead camshaft engine, the DIS ignition coil is mounted near the rear
of the cylinder head.
Each pair of terminals of the DIS ignition coil provides the spark for two spark plugs simultaneously.
The DIS ignition coil is not serviceable and must be replaced as an assembly.
CRANKSHAFT POSITION SENSOR
This direct ignition system uses a magnetic crankshaft position sensor.
This sensor protrudes through its mount to within approximately 1.3 mm (0.05 inch) of the crankshaft reluctor.
The reluctor is a special wheel attached to the crankshaft or crankshaft pulley with 58 slots machined into it, 57 of which are equally spaced in 6 degree intervals.
The last slot is wider and serves to generate a "sync pulse." As the crankshaft rotates, the slots in the
reluctor change the magnetic field of the sensor, creating an induced voltage pulse.
The longer pulse of the 58th slot identifies a specific orientation of the crankshaft and allows the electronic control module (ECM) to determine the crankshaft orientation at all times.
The ECM uses this information to generate timed ignition and injection pulses that it sends to the ignition coils and to the fuel injectors.
IDLE AIR SYSTEM OPERATION
The idle air system operation is controlled by the base idle setting of the throttle body and the idle air control (IAC) valve.
The electronic control module (ECM) uses the IAC valve to set the idle speed dependent on conditions.
The ECM uses information from various inputs, such as coolant temperature, manifold vacuum, etc., for the effective control of the idle speed.
FUEL CONTROL SYSTEM OPERATION
The function of the fuel metering system is to deliver the correct amount of fuel to the engine under all operating conditions.
The fuel is delivered to the engine by the individual fuel injectors mounted into the intake manifold near each cylinder.
The two main fuel control sensors are the manifold absolute pressure (MAP) sensor and the oxygen (O2) sensor.
The MAP sensor measures or senses the intake manifold vacuum.
Under high fuel demands the MAP sensor reads a low vacuum condition, such as wide open throttle.
The electronic control module (ECM) uses this information to richen the mixture, thus increasing the fuel injector on-time, to provide the correct amount of fuel.
When decelerating, the vacuum increases.
This vacuum change is sensed by the MAP sensor and read by the ECM, which then decreases the fuel injector on-time due to the low fuel demand conditions.
The O2 sensor is located in the exhaust manifold.
The O2 sensor indicates to the ECM the amount of oxygen in the exhaust gas and the ECM changes the air/fuel ratio to the engine by controlling the fuel injectors.
The best air/fuel ratio to minimize exhaust emissions is 14.7 to 1, which allows the catalytic converter to operate most efficiently.
Because of the constant measuring and adjusting of the air/fuel ratio, the fuel injection system is called a "closed loop" system.