Swapping a JDM H22A engine into a 1990-1991 Honda Prelude is a popular upgrade for enthusiasts looking to boost performance. While mechanically sound, the electrical wiring aspect, particularly when dealing with the OBD1 system of the 1990 Prelude, can seem daunting. This guide breaks down the essential wiring modifications needed for a successful H22A swap into your 3rd generation Prelude, focusing on making the process as straightforward as possible. Many enthusiasts search for “1990 Prelude Obd2” information, but it’s crucial to clarify that the 1990 Prelude utilizes the OBD1 system. This guide will specifically address the OBD1 wiring nuances for this engine swap.
Understanding Your 1990 Prelude’s OBD1 System
The 1990 and 1991 Honda Preludes are equipped with an OBD1 (On-Board Diagnostics 1) engine management system. This is important to note as some might mistakenly search for “1990 prelude obd2” information. Understanding that your Prelude is OBD1 is the first step to a smooth engine swap. The OBD1 system, while less advanced than OBD2, is robust and well-documented, making it manageable for engine swaps. For 1990-91 Preludes, the good news is that their PGM-FI system and OBD-1 ECU mean you can leverage readily available OBD-1 Honda wiring diagrams. Sensor functions and ECU pin assignments are largely consistent across OBD-1 Honda models of the era. This compatibility simplifies using ECUs like a 1994 P13 ECU in your 1990-91 Prelude without complex connector modifications, as illustrated below.
For owners of earlier 88-89 carburetor-equipped Preludes with the older OBD-0 system, the conversion to PGM-FI and OBD-1 for an H22A swap involves additional steps. This includes potentially swapping to an OBD-0 to OBD-1 wiring harness or manually adapting connectors using wiring diagrams. Carburetor models also require a significant fuel system overhaul, including fuel tank and pump replacement, which is detailed in Honda service manuals. However, for 1990-91 Prelude owners, the focus is primarily on adapting the engine wiring for the H22A within the existing OBD1 framework.
Key Wiring Differences Between B20A and H22A
The most intricate part of the H22A swap wiring lies in accommodating the coil and igniter unit connections. JDM H22A engines often come with inner coil ignition systems, whereas US market H22s and earlier Euro Preludes might utilize external coil setups. This difference necessitates modifications to your Prelude’s original B20A engine harness.
The core strategy for a clean and reliable swap is to utilize your original B20A engine wiring harness as the foundation for the H22A. Instead of trying to adapt the H22A wiring harness to your Prelude, it’s more effective to modify the B20A harness to accommodate the H22A engine’s sensors and connectors. This approach leverages the existing integration with your car’s ECU and electrical system.
Key Differences to Address:
- Distributor Connectors: H22A and B20A distributors use different connectors. This is a primary area requiring modification.
- Coil Connection: The H22A’s inner coil system differs from the external coil setup potentially found on earlier Preludes.
- Oil Pressure Sensor: Connector types may vary.
- MAP Sensor Wiring: While both may not have a dedicated MAP sensor connector on the harness itself (often wired separately), ensure compatibility or adaptation for your chosen MAP sensor setup.
- Additional Sensors on H22A (not on B20A harness):
- VTEC oil pressure sensor and switch
- Knock sensor
- ECT sensor near the thermostat
Step-by-Step Hybrid Wiring Harness Creation
Creating a hybrid wiring harness involves carefully modifying your B20A harness to integrate with the H22A engine. Here’s a breakdown of the process:
Utilizing the B20A Harness as a Base
Begin by removing the wiring harness from your original B20A engine. This will serve as your donor harness. Carefully inspect both the B20A and H22A wiring harnesses. Identify the connectors and wiring that need to be swapped or added. The goal is to transplant necessary connectors and wiring from the H22A harness onto the B20A harness, maintaining the B20A harness’s integration with your Prelude’s ECU and chassis wiring.
Distributor Wiring
The distributor connectors are a major point of difference. The image below clearly shows the distinct connectors.
To address this, obtain the distributor connector from the H22A harness. Cut the B20A distributor connector and splice in the H22A connector, ensuring correct wire matching according to wiring diagrams for both engines. It’s recommended to perform these solder and splice connections closer to the main harness connectors (the “mine connectors” as referred to in the original article) rather than near the distributor itself. This minimizes heat exposure to solder joints and allows for easier access during the swap process.
Coil Connection
For the coil wiring, Preludes originally had an external coil. The H22A with an internal coil distributor needs a different connection. Locate the original external coil connectors (typically a pink and a grey smaller connector with Blue and Black/Yellow wires). These will be disconnected. You will need to adapt the wiring to connect to the H22A distributor’s internal coil and igniter. Specifically, the Yellow/Green wire from the H22A distributor’s igniter unit needs to be connected to ECU pin A21, as shown in wiring diagrams.
For a clean connection, consider sourcing a connector from a later model Honda (like a 4th gen Prelude or Accord) from a junkyard that fits the H22A distributor’s coil wiring. This allows for a secure and reliable plug-in connection rather than just splicing wires directly.
MAP Sensor and Other Sensors
While the original article mentions the MAP sensor being wired separately, ensure you have a compatible MAP sensor setup. Using the stock 3rd gen Prelude MAP sensor is a viable option, as it is OBD1 compatible and connects correctly to the ECU. Mount it securely in the engine bay and connect it to a vacuum line on the intake manifold.
For other sensors like VTEC, knock sensor, and the additional ECT sensor on the H22A, you will need to add wiring and connectors to your B20A harness. Source the necessary connectors from the H22A harness and splice them into the appropriate wires on your modified B20A harness, referencing wiring diagrams for pin assignments.
Essential Connector Compatibilities and Differences
Many connectors are fortunately the same between the B20A and H22A wiring harnesses, simplifying the swap.
Same Connectors:
- Speed sensor
- Lambda (O2) sensor
- Injectors
- Throttle Position Sensor (TPS)
- Intake Air Temperature (IAT) sensor
- Idle valve sensor
- Water temperature sensor (to ECU)
- Water coolant fan sensor
- Water temperature sensor (to dashboard)
- Starter signal sensor
- Shift position sensor
- Alternator sensor
Different Connectors:
- EGR valve lift sensor
- Distributor connectors
- Oil pressure sensor
- Main (“Mine”) connectors to ECU
B20A Harness Lacks Connectors For:
- VTEC oil pressure sensor
- VTEC oil pressure switch sensor
- Knock sensor
- ECT sensor near thermostat on H22A
Conclusion
Successfully wiring an H22A engine into a 1990 Honda Prelude requires a methodical approach, particularly when addressing the nuances of the OBD1 system. By using your original B20A harness as a base and carefully adapting it to the H22A engine’s wiring requirements – especially around the distributor and coil connections – you can achieve a reliable and functional engine swap. Always refer to the Honda wiring diagrams for both the B20A and H22A engines to ensure correct wire splicing and pin assignments. Take your time, double-check your connections, and if you’re ever unsure, consult with a qualified automotive electrician to ensure the wiring is safe and correct. This detailed guide should empower you to tackle the wiring aspect of your 1990 Prelude H22A swap with confidence.
