For automotive enthusiasts looking to enhance the performance of their 90-91 Honda Prelude Si, swapping the original B21 engine with a JDM H22A engine is a popular and effective upgrade. While the mechanical aspects of the swap are relatively straightforward, the electrical wiring, particularly concerning the OBD-1 system in 90-91 Preludes, often presents a challenge. This guide focuses on simplifying the wiring process, highlighting the key considerations and steps for a successful JDM H22A engine swap in your 90 Prelude Si B21 Obd2, ensuring optimal performance and compatibility.
Understanding the Electrical System of the 90-91 Prelude Si
The 1990-1991 Honda Prelude Si models are equipped with the OBD-1 (On-Board Diagnostics 1) system. This is a significant advantage compared to the earlier 88-89 models with OBD-0 systems, especially when undertaking engine swaps. The OBD-1 system in the 90-91 Preludes uses a PGM-FI (Programmed Fuel Injection) system and is internationally standardized, meaning you can utilize generic OBD-1 Honda wiring diagrams as sensor functions and ECU pin configurations are largely consistent across different Honda models of the same era. For instance, a 1994 P13 ECU can be directly connected to your 1990-91 Prelude without requiring connector modifications, demonstrating the system’s adaptability.
An example of an OBD-1 ECU connector, showcasing the standardized interface that simplifies electrical connections in 90-91 Preludes.
Close-up view of OBD-1 ECU connectors, highlighting the pin layout that is consistent with many Honda OBD-1 systems.
For owners of 88-89 Preludes with the older OBD-0 system and carburetor, the electrical conversion to OBD-1 for an H22A swap is more involved. It necessitates either swapping to OBD-1 wiring harness connectors or sourcing OBD-1 ECU connectors from 92-95 Honda models from a junkyard and performing soldering to adapt the wiring. Carbureted models also require a complete overhaul of the fuel and electrical wiring system, including the fuel tank and pump, which is a more extensive task but manageable with the Honda service manual.
Key Electrical Considerations for the JDM H22A Swap
When performing a JDM H22A engine swap, the most intricate part of the electrical work revolves around the coil and igniter unit connections. JDM H22A engines typically feature an inner coil ignition system, whereas US market H22 engines and earlier European Preludes might use external coil ignition systems. This difference mandates specific wiring adjustments during a JDM H22A swap, particularly in older Prelude models designed for external coils.
To navigate the wiring, referencing the correct wiring diagrams is crucial.
Here are wiring diagrams for reference:
H22A OBD-1 92-95 Wiring Diagram
H22A OBD-1 92-95 Wiring Diagram Continued
B20 OBD-1 90-91 Wiring Diagram
While the diagrams appear similar, the physical locations of sensors on the engine and within the car differ between the 3rd and 4th generation Preludes. Despite these differences, approximately 95% of the wiring is conceptually similar, simplifying the adaptation process.
Wiring Harness Compatibility: B20A Harness as a Base
The most effective approach to wiring the H22A engine in a 90-91 Prelude Si is to utilize the original B20A engine wiring harness as the foundation. Instead of attempting to adapt the H22A engine wiring to the car, it’s more efficient to modify the B20A harness to accommodate the H22A engine. This method leverages the existing car-side connectors and wiring, minimizing extensive modifications. The H22A engine’s wiring harness should be retained as a donor source for connectors and wires needed for the hybrid harness.
Comparison of JDM H22A wiring (top) and B20A wiring (bottom), highlighting connector junction points for ECU and relay box connections.
Close-up view of B20A wiring connectors, focusing on connectors for the relay box and alternator power cable.
Image showing injector connectors, which are noted to be the same as idle valve connectors and compatible between B20A and H22A.
Visual of alternator connectors, indicating similarity and potential compatibility between B20A and H22A setups.
Key differences to note between the harnesses include the distributor connectors, which are visibly different.
Distributor connectors comparison, with grey H22A connectors shown to be different from B20A connectors, requiring adaptation.
Also, the oil pressure sensor connectors differ in style – plug type for H22A versus bolt-connected for B20A. Notably, neither the H22A nor B20A wiring includes a dedicated MAP sensor connector; the MAP sensor wiring is separate and runs directly to the ECU. For this swap, the stock 3rd generation Prelude MAP sensor can be reused, connected to the intake manifold vacuum line and ECU, ensuring OBD-1 compatibility without wiring modifications.
Distributor and Coil Wiring – The Main Challenge
The distributor connection is a primary area requiring modification. The JDM H22A distributor integrates sensors like CYL (Cylinder sensor), TDC (Top Dead Center sensor), CKP (Crankshaft Position sensor), and the ICM (Igniter Control Module). The connectors are different from the B20A distributor connectors. When modifying the wiring, it’s advisable to change the entire length of the distributor wires up to the main connectors, performing solder work near the larger white connectors away from the engine’s heat and potential physical disturbances during the swap process.
Image highlighting the distributor connector and the igniter unit cable (Yellow/Green) that connects to ECU pin A21, crucial for ignition system integration.
Close view of the JDM H22A distributor with its built-in igniter unit, emphasizing the integrated ignition components.
Another view of the distributor components, illustrating the sensors and integrated coil setup.
Regarding the coil connection, 3rd generation Preludes originally have an external coil located in the engine bay near the main connectors.
Location of the external coil in a 3rd generation Prelude engine bay, indicated by a red circle, which will be bypassed in favor of the H22A’s internal coil.
This external coil and its smaller connectors (pink and grey) with blue and black/yellow cables will be bypassed when using the H22A’s internal coil. Only the larger gauge wires are needed.
Depiction of modified coil wiring, showing the adaptation needed to connect the H22A’s internal coil system.
Example of a safe connector used in the modified wiring, suggesting the use of junkyard connectors from 4th gen Preludes or Accords for reliable connections.
MAP Sensor and Other Connections
As mentioned, the MAP sensor from the 3rd gen Prelude is compatible and can be reused without wiring modifications. Many other sensor connectors are also compatible between the B20A and H22A wiring, including:
- Speed sensor
- Lambda (O2) sensor
- Injectors
- TP (Throttle Position) sensor
- IAT (Intake Air Temperature) sensor
- Idle valve sensor
- Water temperature sensor (to ECU and dash)
- Water coolant fan sensor
- Starter signal sensor
- Shift position sensor
- Alternator sensor
However, differences exist in connectors for:
- EGR valve lift sensor
- Distributor connectors
- Oil pressure connector
And the B20A wiring lacks connectors for:
- VTEC oil pressure sensor and switch
- Knock sensor
- ECT sensor near thermostat on H22A
By combining the B20A wiring harness as a base and incorporating necessary connectors and wiring from the H22A harness, a hybrid harness can be constructed.
Schematic of a hybrid wiring harness skeleton, illustrating the modified B20A harness adapted for the H22A engine.
Example of a completed and modified wiring harness, ready for installation, emphasizing organized and secure connections.
Ensure all soldered connections are well-insulated, especially those for the distributor and knock sensor. After modification, test fit the harness on the engine to confirm proper wire lengths and connector fitment before final installation.
Conclusion: Achieving a Successful OBD-1 H22A Swap in your 90-91 Prelude Si
Successfully wiring a JDM H22A engine into your 90 Prelude Si B21 OBD2 involves careful attention to detail, particularly in adapting the wiring harness for the distributor and coil. By leveraging the existing B20A harness and understanding the subtle differences in sensor connectors, you can create a reliable and efficient electrical system for your upgraded Prelude. With patience and the correct wiring diagrams, this electrical aspect of the H22A swap becomes a manageable task, allowing you to enjoy the enhanced performance of your Honda Prelude. Feel free to consult online communities and forums for further assistance and to share your experiences.
