The distributor in your B-series Honda engine, especially if it’s an OBD2 system, is a critical component often misunderstood. It’s responsible for more than just spark distribution; it’s also a hub for essential engine sensors. Tampering with the distributor position can severely impact your engine’s timing and lead to significant damage if you’re not familiar with the adjustment process. Therefore, if you lack experience in setting ignition timing, it’s crucial to avoid removing or even touching the distributor. This guide will delve into the intricacies of the Obd2 B Series Distributor, outlining its vital functions, key components, and necessary maintenance. While primarily referencing an OBD-1 distributor for visual clarity, the principles and explanations largely apply to OBD-2 systems as well, with minor differences mainly in the harness plug configuration.
Why is the Distributor Important?
The B-series engine distributor is paramount for two primary reasons:
Ignition Control
Firstly, it directly controls the engine’s ignition system. It houses the components responsible for generating and distributing the high-voltage spark needed to ignite the air-fuel mixture in each cylinder at precisely the right moment.
Sensor Housing
Secondly, the distributor acts as a housing for several crucial sensors that the Engine Control Unit (ECU) relies upon for proper engine management.
It’s important to note that while the distributor houses vital sensors, other critical sensors like the Throttle Position Sensor (TPS), Manifold Absolute Pressure (MAP), and temperature sensors are located elsewhere on the engine.
To illustrate the complexity, here’s a schematic of an OBD-2 distributor, derived from the official Helms manual:
Distributor Sensors in Detail
Let’s explore the three key sensors located within the B-series distributor:
- TDC Sensor (Top Dead Center): This sensor signals to the ECU when a piston is at its highest point in the cylinder (Top Dead Center) on the compression stroke. This is crucial for timing calculations.
- CYP Sensor (Cylinder Position): The CYP sensor identifies which cylinder is approaching its firing point. This is essential for sequential fuel injection and ignition in OBD2 systems.
- CKP Sensor (Crankshaft Position): While some B-series engines have a CKP sensor externally on the crankshaft, those integrated into the distributor provide crankshaft position information to the ECU. This data is vital for determining engine speed and precise timing.
These sensors are “Hall effect” sensors. While the intricate physics are complex, the basic principle involves detecting interruptions in a magnetic field. When a part of the distributor shaft, equipped with specific teeth or reluctors, passes through the sensor, it disrupts the magnetic field, causing a voltage change. This change is then interpreted by the ECU as positional information. For a more in-depth technical explanation, you can refer to resources like the Wikipedia page on the Hall effect.
Each sensor comprises two main parts: the sensor itself (typically the black electronic component) and the corresponding reluctor or trigger component mounted on the distributor shaft. Here’s a visual representation of these sensors within a disassembled distributor:
Note: While the labeling in the image is based on logical deduction, definitive confirmation would require detailed wire color analysis and testing. Sensor failures are not frequently reported, but like any electronic component, they are susceptible to malfunction over time.
The Ignition System: Coil and ICM
Now, let’s delve into the ignition aspect of the distributor, arguably its most critical function.
The Ignition Coil
The heart of the ignition system within the distributor is the ignition coil. It’s an induction coil designed to convert the car’s 12V electrical system into the high voltage necessary to create a spark across the spark plug gap. For a deeper understanding of induction coils, resources like the Wikipedia article on induction coils can be helpful.
The coil works by applying 12V to its primary windings. Inside these primary windings is a secondary coil with a significantly larger number of windings. When the 12V supply to the primary coil is abruptly cut off, the magnetic field generated around it collapses rapidly. This collapse induces a high-voltage pulse in the secondary coil, resulting in the spark needed for ignition.
To examine the coil, we need to disassemble the distributor. First, remove the distributor cap (usually secured by three screws) and then the rotor (held by a single screw, which can sometimes be tight). Next, carefully remove the dust cover. You’ll find two wires connected to the coil; unscrew these, being cautious as they might be fragile due to age. Finally, remove the two larger screws located on top of the coil, as shown here:
With these screws removed, the coil can be carefully pulled out of the distributor housing:
The Ignition Control Module (ICM)
Next is the Ignition Control Module (ICM), sometimes referred to as the Igniter. Think of it as a sophisticated, high-speed switch or relay. Its primary function is to control the “dwell time,” which is the duration the ignition coil is energized with 12V. The ICM also manages the crucial task of interrupting the voltage supply to the coil at the precise moment to trigger the spark. Furthermore, the ICM generates the tachometer signal, which is why erratic tachometer behavior can often indicate an ICM issue.
The ICM typically has four wire connections: +12V supply, coil control wire, tachometer output, and an input from the ECU. The ICM grounds to the distributor body externally.
To remove the ICM, first disconnect the four wires. Their positions are usually distinct, making reconnection straightforward. Then, remove the two screws securing it to the distributor housing:
Here’s a closer look at the ICM itself:
ICM Failure Symptoms
As these vehicles age, ICM failures are becoming increasingly common. Symptoms of a failing ICM can include:
- Random tachometer jumping or erratic readings.
- A completely unresponsive tachometer.
- Sudden engine shut-off while driving, where the engine abruptly stops, potentially with the tachometer malfunctioning, and a loss of power.
OEM Ignition System Reliability
The original equipment manufacturer (OEM) Honda ignition system is known for its robustness. While aftermarket ignition enhancements like MSD or Crane systems and external coils exist, experience suggests they often introduce more problems than benefits in stock or mildly modified applications. There are numerous accounts of aftermarket coils prematurely failing ICMs. The OEM Honda ignition system is demonstrably capable of handling significant power levels. This isn’t to say all aftermarket ignition products are inherently flawed, but rather to highlight the well-engineered harmony between the Honda ICM and coil. For most applications, replacing faulty components within the OEM system is a more reliable approach than wholesale aftermarket upgrades.
Spark Distribution: Cap and Rotor
After the coil generates the high-voltage spark, it travels through the center tower of the distributor cap, down to the rotor, and then out to each spark plug wire in sequence.
Reassembly is the reverse of disassembly. Ensure spark plug wires are connected to the correct terminals on the distributor cap, following the engine’s firing order. The coil wires are designed with different connectors – a circular one for the +12V harness connection and a square one for the ICM wire. Similarly, the ICM wires have specific lengths that facilitate correct orientation during reassembly.
While not explicitly detailed here, the rotor and distributor cap are also subject to wear and tear. Rotor screws can loosen over time, potentially causing the rotor to detach from the distributor shaft. This can lead to a no-start condition and potential physical damage. When reinstalling the rotor, while it can only be installed in one orientation, applying a small amount of blue (medium-strength) Loctite to the rotor screw is a prudent measure for added security.
Maintenance and Rotor Screw Security
Regular maintenance of your distributor’s ignition components is crucial. Honda, along with many mechanics, recommends periodic replacement of the distributor cap and rotor, ideally every year or two, depending on driving conditions and mileage. Proactive replacement of these relatively inexpensive parts can prevent ignition issues and maintain optimal engine performance.
Conclusion
The OBD2 B series distributor is a vital and intricate component in your Honda engine. Understanding its functions, sensors, and ignition system components is essential for proper maintenance and troubleshooting. Remember, while aftermarket upgrades might seem appealing, the OEM ignition system is robust and reliable for most applications. Prioritize regular maintenance and component replacement to ensure the longevity and performance of your B-series engine. And always exercise caution when working on the distributor, especially regarding timing adjustments, to avoid potential engine damage.
