Swapping an H22A4 engine into your older Honda? This comprehensive guide focuses on the critical ECU aspect of converting from OBD1 to OBD2 when using an H22A4 (found in 97+ USDM Preludes) or a Type-S H22A. We’ll cover wiring, distributor compatibility, and essential tips for a successful engine swap.
Simplifying the OBD2 to OBD1 Conversion
While converting your OBD1 vehicle to OBD2a is possible, it’s a complex process rarely undertaken. This guide focuses on the simpler and more common approach: using an OBD1 distributor, injectors, and ECU with your OBD2 H22A4 engine. This allows you to retain your existing wiring harness and simplifies the overall swap process.
Distributor Wiring: OBD2 to OBD1
The key to a successful swap lies in correctly wiring the distributor. Here’s a breakdown of the conversion process:
This diagram illustrates the wiring connections needed to adapt the OBD2 distributor to function with an OBD1 ECU. Understanding these connections is crucial for proper engine operation.
Internal vs. External Coil Considerations
Internal Coil: If your car originally had an internal coil, the JDM H22 distributor will plug in directly.
External Coil: If your car had an external coil, you have two options:
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Modify the Coil Plug: Splice the yellow and yellow/black wires from the stock coil plug together. This creates the necessary connection for the JDM distributor. The black/white wire is not used. Alternatively, insert a 30-amp fuse into the plug to connect these wires.
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Retain the External Coil: Open the JDM distributor and remove the internal coil. Connect the wire from the igniter (originally connected to the internal coil) to the empty pin on the distributor plug. Use a 93-95 Prelude VTEC distributor cap and rotor.
Distributor Cap and Rotor Selection
Choosing the correct distributor cap and rotor is essential for spark delivery:
- Internal Coil: Use the original CB7 internal coil cap and rotor or those from a 2000 Civic Si.
- External Coil: Use a cap and rotor from a 93-95 Prelude VTEC.
Aftermarket Ignition Amplifier Installation (MSD/Crane)
For vehicles with an external coil and an aftermarket ignition amplifier:
- Cut off the stock coil plug.
- Splice the yellow and yellow/black wires together and connect them to the ignition input (typically red) on the amplifier.
- Connect the black/white wire to the trigger input (typically white) on the amplifier.
Pinouts for OBD1 ECU (H22 Swaps)
When using an OBD1 ECU with an H22 swap, ensure the following pin connections are correct:
- VTEC Solenoid: Pin A4
- VTEC Pressure Switch: Pin D6
- Knock Sensor: Pin D3
- Secondary Intake Solenoid: Pin A17 (Connect black/yellow wire to switched ignition)
- FPR Solenoid: Pin A10 (Connect black/yellow wire to switched ignition – not present on all H22s)
Important Note: If using a 94-95 Accord ECU (P0A/P0B), swap pins A6 and A11 on the ECU harness due to wiring differences between the 4th and 5th generation Accords.
Sourcing ECU Pins
Junkyards are a great source for ECU pins. Locate any OBD1 Honda, cut out the ECU harness, and extract the necessary pins for your swap.
Conclusion: Achieving a Successful H22 Swap
Successfully integrating an H22A4 into an older Honda requires careful attention to detail, particularly regarding the ECU and distributor. By following this guide and understanding the key differences between OBD1 and OBD2 systems, you can confidently tackle your engine swap project. Remember to consult your vehicle’s wiring diagrams and always double-check your connections before starting the engine.
