So, you’re diving into the world of Honda engine swaps and facing the inevitable hurdle of wiring harnesses? If you’re putting an OBD2 engine into an older OBD1 Honda chassis, you’ve likely encountered the term “OBD2 to OBD1 conversion harness.” While there are several ways to tackle this, using a Honda Obd2 To Obd1 Harness, specifically an OBD2 USDM Integra engine harness, stands out as a superior method. Let’s explore why this is the preferred route and how to navigate your options.
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Why an OBD2 Integra Harness is the Smart Choice
Forget about the headaches of splicing wires or investing in a bunch of adapters. The beauty of using a honda obd2 to obd1 harness from a USDM (United States Domestic Market) Integra lies in its near plug-and-play nature. Here’s why it’s a step above other approaches:
- Direct Connection at Strut Towers: Unlike OBD2 Civic harnesses which are often one-piece designs requiring more extensive modification, Integra harnesses are two-piece. This crucial design feature means they have plugs conveniently located at the strut towers, just like your OBD1 Civic harness. This allows for a much cleaner and simpler integration.
- Avoids Unnecessary Modifications: With an OBD2 Integra harness, you can largely bypass modifications to key engine components. The alternator, injectors, and distributor typically remain plug-and-play, saving you time and potential wiring errors. The older methods of swapping to OBD1 parts or aggressively splicing OBD2 harnesses are not only more complex but frankly, unnecessary with this smarter approach.
- Cost-Effective and Accessible: While OBD1 USDM P72 ECUs (Engine Control Units) can be expensive and harder to find, 96+ Integras are commonly found in junkyards like Pick Your Part. This makes sourcing a suitable OBD2 Integra engine harness relatively easy and budget-friendly. Just remember, steer clear of JDM (Japanese Domestic Market) harnesses as they are designed for right-hand drive vehicles and are often found damaged or cut.
Navigating Your ECU Options with a Honda OBD2 to OBD1 Harness
Once you’ve installed your OBD2 Integra honda obd2 to obd1 harness, you’ll find a leftover plug – simply secure it out of the way with a zip tie. Now, you have several paths to choose from regarding your ECU setup. Here are the most common and effective options:
Option 1: The OBD1 USDM Manual P72 ECU Route
Traditionally favored, this involves using an OBD1 USDM manual P72 ECU. You would plug this directly into your Civic ECU harness (now connected via the Integra harness), and then add pins to your ECU harness for features like knock control, IABs (Intake Air Bypass System), and VTEC (Variable Valve Timing and Lift Electronic Control). While effective, manual P72 ECUs are becoming increasingly rare and expensive.
Option 2: OBD1 Automatic P72 ECU Conversion
A smart alternative to Option 1 is to acquire an OBD1 automatic P72 ECU. These are significantly cheaper and more readily available than their manual counterparts. The conversion to manual is straightforward and well-documented, making this a cost-effective solution.
Option 3: Chipped P06 or P28 ECU for Tuning Flexibility
For those seeking maximum tuning capability, using a P06 or P28 ECU that is chipped and flashed with a B18C1 tune is highly recommended. You’ll need to modify the circuit board to incorporate IABs and VTEC (P28 already has VTEC). While this might require professional assistance, the major advantage is the ability to get a custom dyno tune, optimizing your engine’s performance. While Options 1 and 2 ECUs can also be chipped and tuned, starting with a P06/P28 often simplifies the process and can be more economical in the long run if tuning is your priority.
Option 4: OBD2 Manual P72 ECU with Conversion Harness
OBD2 P72 ECUs are generally inexpensive and easier to locate. By pairing an OBD2 manual P72 with a dedicated OBD1 to OBD2 conversion harness (readily available from suppliers like Rywire), you create a viable setup. This option requires bypassing the CKF (Crankshaft Fluctuation Sensor) and adding wiring for knock control, but these are relatively simple procedures. You’ll also need to add a secondary O2 sensor bung downstream of your catalytic converter. Option 4 is often considered a legitimate and legal option for passing emissions testing in stricter regions.
Option 5: JDM OBD2 P72 ECU for Budget Builds (with Caveats)
The JDM OBD2 P72 ECU combined with an OBD1 to JDM OBD2 conversion harness is often the most budget-friendly and easiest to implement. However, it’s crucial to be aware that this setup likely won’t pass BAR (Bureau of Automotive Repair) in California and may face similar regulatory issues in other regions with stringent emissions standards. This option is best suited for off-road or track applications where emissions compliance is not a primary concern.
Conclusion: Choosing the Right Honda OBD2 to OBD1 Harness Strategy
Converting from OBD2 to OBD1 in your Honda engine swap doesn’t have to be a wiring nightmare. Utilizing a honda obd2 to obd1 harness based on a USDM Integra harness simplifies the process significantly, offering a cleaner, more cost-effective, and less intrusive method compared to older techniques. When selecting your ECU option, consider your budget, tuning goals, and local emissions regulations. Options 3 and 4 provide excellent balances of performance, tunability, and legality for most enthusiasts. Remember to consult with experienced tuners or mechanics if you are unsure about any step of this conversion process.
