The electronic distributor ignition systems used on the Accord and Prelude models is similar to a distributor with the conventional breaker point ignition system found on earlier vehicles. Both systems use a distributor cap and ignition rotor to distribute the ignition spark from the ignition coil to each cylinder's spark plug in the correct order. They both require the cap and rotor to be inspected cleaned and/or replaced during periodic maintenance.
The main difference between the two systems is that the electronic distributor does not have any moving parts that require periodic adjustments, unlike breaker points, which require periodic rubbing block lubrication, adjustment and replacement. To advance the ignition timing relative to engine speed, the breaker point and the initial electronic ignition systems used a mechanical, centrifugal advance unit. The ignition timing would advance based solely on the engine's speed. Those systems worked well for their day, however to meet today's more stringent emission standards, an engine's operating efficiency must be optimized. To meet these standards, and optimize an engine's efficiency requires precise control of the ignition timing.
To achieve this level of efficiency, the ignition timing advance is controlled electronically by the Powertrain Control Module (PCM). This allows the ignition timing to be adjusted electronically based on input from a collection of electronic sensors. This system allows the ignition timing advance to be adjusted and optimized instantly, for changes in engine speed, intake manifold airflow rate and the engine coolant temperature. Some vehicles may have a knock control system, which sets the ideal ignition timing for the octane rating of the gasoline being used.
There are three sensors used to supply information to the PCM. These sensors are the Top Dead Center (TDC), Crankshaft Position (CKP), and Cylinder Position (CYP) sensors. The information these sensors supply to the PCM allows the control module to monitor the mechanical moving components of the engine. The CKP sensor determines the timing for fuel injection and ignition for each cylinder and detects engine speed. The TDC sensor determines ignition timing during start-up and when the crank angle is abnormal. The CYP sensor detects the position of the No. 1 cylinder for sequential fuel injection to each cylinder
Each sensor is each triggered electronically by a reluctor. The reluctors are installed securely onto the distributor shaft, and rotate with the shaft. One reluctor that is pressed onto the distributor shaft looks very similar to a small straight cut gear. As the reluctor rotates with the distributor shaft, the teeth of the reluctor pass very closely to a small sensor, which is simply a small electric coil. As the teeth of the reluctor move toward the sensor, the electric field of the sensor is energized. As the teeth of the reluctor move past the sensor, the electric field of the sensor is collapsed, causing an electric pulse that is sent from the sensor to the control module. As each tooth of the reluctor passes the sensor, it causes an electrical pulse. For each complete revolution of the distributor shaft, the number of pulses generated per revolution, is equal to the number of teeth on the reluctor. The control module uses these electric pulses to gather information about the engine. The faster the engine spins, the faster the distributor spins, the faster the pulses are generated, which allows the control unit to know how fast the engine is spinning.
Reluctors vary is size and shape. Some reluctors look very similar to small gears, however their shape does vary. Another reluctor found in the distributor, has only one tooth, or raised edge. The shape of the reluctor is mostly rounded, with an oblong ramp leading up to a single raised edge. This reluctor operates just like the gear shaped type, however, because it only has one raised edge to pass by the sensor, only one electric pulse is generated for each revolution of the distributor. The control module uses the single pulse of the CYP sensor to recognize the position of No. 1 cylinder for sequential fuel injection to each cylinder.
As the distributor shaft rotates with the attached reluctors, the electrical pulses for each sensor are used by the control module to track the mechanical moving components of the engine. This allows the control module to keep track of each phase of the four-stroke cycle for each cylinder. The Powertrain Control Module (PCM) can optimize the ignition timing and the amount of ignition advance for the engine's operating conditions (rpm, load and temperature).
The basic ignition timing information for the engine's operating conditions is stored in the memory of the PCM. This is why a jumper must be temporarily installed onto the Service Connector (SCS) when adjusting the idle speed ignition timing as described in the ignition timing adjustment procedure in Section 1 of this guide. Using the jumper allows the base ignition timing to be adjusted manually without the control module over-riding the adjustment. Once the jumper is removed, the control module stores the base timing information into its memory.
As the PCM control module receives input from its sensors, it selects the optimal ignition timing and triggers the ignition coil by sending electric pulses. As with the reluctor collapsing the electrical field of the sensors, the PCM does much the same with the ignition coil. The electrical pulses from the PCM are used to trigger the ignition coil. To do this, the primary ignition current is momentarily cut off by the Powertrain Control Module (PCM). This allows the magnetic field of the ignition coil to collapse, creating a spark that the distributor passes onto the spark plugs via the rotor and spark plug wires.
On 4-cylinder engines, the ignition coil is located within the distributor housing, eliminating the need for a high-tension wire from the ignition coil to the distributor cap. The only high-tension ignition wires used on this ignition system are the spark plug wires, which are connected to the distributor cap and the spark plugs. The V6 engines use a remotely mounted the ignition coil assembly, located near the distributor.