See Figures 1, 2 and 3
The distributorless ignition system is referred to as the Direct Ignition System (DIS). This system's three main components are the coil pack, crankshaft sensor, and camshaft sensor. The crankshaft and camshaft sensors are Hall effect devices.
The ignition system is regulated by the Powertrain Control Module (PCM). The PCM supplies battery voltage to the ignition coil through the Auto Shutdown (ASD) relay. The PCM also controls the ground circuit for the ignition coil. By switching the ground path for the coil on and off, the PCM adjusts the ignition timing to meet changing engine operating conditions.
During the crank/start, period the PCM advances ignition timing a set amount. During engine operation, the amount of spark advance provided by the PCM is determined by these input factors:
The PCM also regulates the fuel injection system.
The camshaft position sensor provides fuel injection synchronization and cylinder identification information. The sensor generates pulses that serve as input to the PCM. The PCM interprets the camshaft position sensor input (along with the crankshaft position sensor input) to determine crankshaft position. The PCM uses the crankshaft position sensor input to determine injector sequence and ignition timing.
The camshaft position sensor is mounted to the rear of the cylinder head. A target magnet attaches to the rear of the camshaft and indexes to the correct position. The target magnet has four different poles arranged in an asymmetrical pattern. As the target magnet rotates, the camshaft position sensor recognizes the change in polarity. The sensor switches from high (5 volts) to low (0.3 volts) as the target magnet rotates. When the north pole of the target magnet passes under the sensor, the output switches high. The sensor output switches low when the south pole of the target magnet passes underneath.
The PCM uses the camshaft position sensor to determine injector sequence. The PCM determines ignition timing from the crankshaft position sensor. Once the crankshaft position has been determined, the PCM begins energizing the injectors in sequence.
The crankshaft position sensor is mounted to the engine block behind the alternator, just above the oil filter. The second crankshaft counterweight has machined into it two sets of four timing reference notches, including a 60 degree signature notch. From the crankshaft position sensor input, the PCM determines engine speed and crankshaft angle (position). The notches generate pulses front high to low in the crankshaft position sensor output voltage. When a metal portion of the counterweight aligns with the crankshaft position sensor, the sensor output voltage goes low (less than 0.5 volts). When a notch aligns with the sensor, voltage goes high (5.0 volts). As a group of notches pass under the sensor, the output voltage switches from low (metal) to high (notch), then back to low.
From the frequency of the output voltage pulses, the PCM calculates engine speed. The width of the pulses represent the amount of time the output voltage stays high before switching back to low. The period of time the voltage stays high before returning to low is called a pulse width. The faster the engine is operating, the smaller the pulse width.
By counting the pulses and referencing the pulse from the 60 degree signature notch, the PCM
calculates crankshaft angle (position). In each group of timing reference notches, the first notch represents 69 degrees Before Top Dead Center (BTDC). The second notch represents 49 degrees BTDC. The third notch represents 29 degrees. The last notch in each set represents 9 degrees BTDC.
The timing reference notches are machined at 20 degree increments. From the voltage pulse-width, the PCM tells the difference between the timing reference notches and the 60 degree reference notches. The 60 degree signature notch produces a longer pulse-width than the smaller timing reference notches. If the camshaft position sensor input switches from high to low when the 60 degree signature notch passes under the crankshaft position sensor, the PCM knows cylinder No. 1 is the next cylinder at TDC.
The ignition coil assembly consists of 2 coils molded together. The assembly is mounted on top of the engine. The number of each coil appears on the front of the coil pack.
High tension leads route to each cylinder from the coil. The coil fires two spark plugs every power stroke; one plug is the cylinder under compression, the other cylinder fires on the exhaust stroke. The PCM determines which of the coils to charge and fire at the correct time. The coil's low primary resistance allows the PCM to fully charge the coil for each firing.