Swapping an SR20DET engine into a Nissan 200SX (B14) originally equipped with a GA16DE engine is a popular upgrade for car enthusiasts looking for more power. However, this swap often involves dealing with different OBD (On-Board Diagnostics) systems. The GA16DE in a 1996 200SX is OBD2, while many SR20DET engines, particularly older ones like the U12, are OBD1. This difference necessitates addressing the wiring harness to ensure everything functions correctly, from the engine itself to your car’s accessories and dashboard.
This guide will walk you through the process of changing your wiring harness from OBD2 to OBD1 for an SR20DET swap in your B14 200SX. We’ll cover the challenges, solutions, and considerations to make your swap as smooth as possible.
Understanding the OBD2 to OBD1 Wiring Challenge
The primary hurdle when swapping an OBD1 SR20DET into an OBD2 vehicle is the electrical system. OBD2 systems are more advanced, with different sensor layouts, ECU (Engine Control Unit) connectors, and diagnostic protocols compared to OBD1. Directly plugging an OBD1 engine and its harness into an OBD2 car will lead to significant compatibility issues.
The key issues you’ll encounter include:
- ECU Connectors: OBD1 and OBD2 ECUs have different pinouts and connector styles. The OBD2 chassis harness in your 200SX won’t directly plug into an OBD1 SR20DET ECU.
- Sensor Differences: While many sensors might perform similar functions, their wiring and signal outputs can differ between OBD1 and OBD2 systems.
- Accessory Integration: You need to ensure crucial car accessories like the air conditioning, speedometer, tachometer, and other gauges function correctly after the swap.
- Wiring Complexity: Attempting to directly hardwire an OBD1 harness into an OBD2 car can be extremely complex and time-consuming, requiring extensive wiring diagrams and expertise.
Solutions for OBD2 to OBD1 Wiring Conversion
Fortunately, there are several solutions to overcome the wiring differences when performing an OBD1 SR20DET swap into an OBD2 B14 200SX.
1. OBD2 to OBD1 Conversion Harness
The most common and often recommended solution is using an OBD2 to OBD1 conversion harness. This adapter harness bridges the gap between your OBD2 chassis harness and the OBD1 SR20DET engine harness and ECU.
How it works:
- The conversion harness has OBD2 connectors on one end that plug directly into your car’s original engine harness connectors.
- On the other end, it has OBD1 connectors that are compatible with the SR20DET engine harness and ECU.
- The harness is designed to properly translate the necessary signals, allowing the OBD1 ECU to communicate with your OBD2 car’s systems.
Benefits:
- Simplified Wiring: It significantly reduces the complexity of wiring, making the swap much easier and faster.
- Plug-and-Play (Mostly): While not entirely plug-and-play, it eliminates the need for extensive wire tracing and splicing.
- Retains OBD1 ECU Functionality: Allows you to use the OBD1 SR20DET ECU, which might be preferable for tuning and performance in some cases.
Considerations:
- Harness Quality: Choose a reputable supplier for the conversion harness to ensure quality and proper wiring.
- Compatibility: Confirm the harness is specifically designed for your car model (B14 200SX) and the specific SR20DET engine (U12 in this case).
- Potential Modifications: Depending on the harness and your specific setup, minor modifications might still be needed, such as wiring for the MAF sensor (Mass Air Flow sensor).
2. Using an OBD2 SR20DET Harness (if available)
Another approach, if feasible, is to use an OBD2 SR20DET engine harness. SR20DET engines were produced in both OBD1 and OBD2 versions. If you can source an OBD2 SR20DET harness and ECU (from a later model SR20DET or a compatible vehicle), this can simplify the wiring process.
How it works:
- An OBD2 SR20DET harness is designed to be compatible with OBD2 systems.
- In theory, it should plug more directly into your OBD2 B14 200SX’s chassis harness.
Benefits:
- Potentially Easier Integration: Might offer a more direct fit with your OBD2 car’s electrical system compared to forcing an OBD1 harness to work.
- OBD2 Compliance: If emissions testing is a concern in your region (though the original poster mentioned it’s not), using an OBD2 system could be advantageous.
Considerations:
- Availability: OBD2 SR20DET harnesses and ECUs might be harder to find and potentially more expensive than OBD1 counterparts.
- Engine Compatibility: Ensure the OBD2 harness is compatible with your specific SR20DET engine variant.
- Still Requires Adaptation: Even with an OBD2 harness, some level of adaptation or wiring modification might still be necessary to fully integrate with your B14 200SX, especially concerning accessories and gauges.
3. Full OBD2 Car and Engine Harness Swap (Most Complex)
The most complex and generally least recommended approach is to attempt a complete swap of the entire engine and chassis wiring harnesses to match the OBD1 SR20DET system. This would involve replacing significant portions of your car’s wiring, which is a massive undertaking.
Why it’s not recommended:
- Extreme Complexity: This is a highly complex and time-consuming task, requiring deep electrical knowledge and extensive rewiring.
- Increased Risk of Errors: The chances of wiring errors and issues are significantly higher with such a comprehensive rewire.
- Potentially Unnecessary: Conversion harnesses offer a much simpler and more practical solution in most cases.
Key Wiring Considerations and Accessories
Regardless of the chosen solution, certain wiring aspects and accessory integrations need careful attention:
- Alternator Wiring: As mentioned in the original forum, the GA16DE alternator plug might fit the SR20DET alternator. However, always verify compatibility and wiring if needed.
- Cooling Fans: Wiring for the radiator cooling fans will need to be addressed to ensure they function correctly with the SR20DET.
- Air Conditioning (A/C): Retaining A/C functionality is a common concern for daily drivers. Research and confirm if the GA16DE A/C bracket can be modified to work with the SR20DET, as suggested in the forum. Wiring for the A/C compressor clutch will also need to be integrated.
- Dashboard Gauges (Speedometer, Tachometer, etc.): Ensure the conversion harness or wiring solution properly integrates the signals for your car’s gauges to function accurately with the SR20DET.
- MAF Sensor Wiring: Depending on the MAF sensor you are using with the SR20DET, you might need to modify the wiring plug to match. There are guides available online for common MAF sensor wiring modifications for SR20DET swaps.
Choosing the Right Approach
For most DIYers performing an SR20DET swap into a B14 200SX, using an OBD2 to OBD1 conversion harness is the most practical and recommended solution. It strikes a balance between complexity, cost, and functionality.
Recommendation:
- Research Conversion Harnesses: Look for reputable vendors specializing in SR20DET swap harnesses.
- Verify Compatibility: Double-check that the harness is compatible with your specific car (OBD2 B14 200SX) and engine (OBD1 U12 SR20DET).
- Plan for Accessories: Investigate and plan for the wiring of accessories like A/C and cooling fans.
- Seek Expert Advice: Consult online forums and communities dedicated to SR20DET swaps for specific tips and guidance related to your car model and engine.
Conclusion
Changing the wiring harness when swapping from OBD2 to OBD1 for an SR20DET engine in a B14 200SX is a crucial step. While it might seem daunting, using an OBD2 to OBD1 conversion harness simplifies the process significantly. By understanding the challenges, exploring the solutions, and carefully planning your wiring, you can successfully complete your SR20DET swap and enjoy the enhanced performance in your Nissan 200SX. Remember to prioritize safety, double-check all connections, and seek help from experienced individuals or resources when needed. Happy swapping!
