95 EG Civic OBD2 Conversion: The Ultimate Guide

Swapping a more modern OBD2 B-series engine into a classic 92-95 Honda Civic (EG chassis) or DC Integra is a popular upgrade. If you’re diving into this exciting project, understanding how to get that OBD2 engine running smoothly in your OBD1 chassis is crucial. This guide provides a clear and concise breakdown of how to perform this conversion, focusing on using an OBD1 ECU or navigating the complexities of an OBD2 ECU setup in your OBD1 Honda.

Understanding OBD1 and OBD2 Differences in 92-95 Hondas

The 92-95 Honda Civic, Del Sol, and Integra models are all natively OBD1 (On-Board Diagnostics 1). This means their electronic systems, including the ECU (Engine Control Unit), sensors, and wiring, adhere to the OBD1 standard. A key advantage of OBD1 Hondas is the interchangeability of OBD1 electronic components across various models within the same engine series (B or D series). You could generally swap distributors, injectors, ECUs, and engine wiring harnesses among 92-95 Civics, Del Sols, and Integras, simplifying modifications.

However, when you introduce an OBD2 engine – common in later model Integras and Civic Sis – into this OBD1 system, compatibility challenges arise. OBD2 systems are more complex, featuring additional sensors and different wiring configurations. This guide focuses on bridging this gap, specifically for ’95 EG Civic owners looking to convert to OBD2 engine management.

Essential Parts for Your 95 EG OBD2 Engine Swap

To successfully install an OBD2 B-series engine into your 95 EG Civic or DC Integra chassis, you’ll need specific components. Importantly, ’94-95 Integra owners can reuse some existing parts mentioned below.

Front Transmission Bracket: You’ll need a front transmission bracket from a ’94-01 Integra or ’99-00 Civic Si (compatible with any 5-speed model).
Rear Engine “L” Shaped Bracket: Source this rear engine bracket from a ’94-01 Integra (any 5-speed model).
Driver Side 3-Post Mount: Required if you’re installing a B18B/C/C5 engine. This mount is not necessary if you’re using an OBD2 B16/B17 engine. Note that for OBD2 B16A swaps, you can reuse your existing Civic/Del Sol driver side dual-post mount.
A/C Bracket: Obtain an A/C bracket from a ’94-01 Integra or ’99-00 Civic Si if you plan to retain air conditioning.
Complete Shift Linkage: Use a complete shift linkage from a ’94-01 Integra or ’99-00 Civic Si. Crucially, Del Sol owners must use a B-series Del Sol specific shift linkage, which can be harder to find used but is available new from Honda.
Complete Axles with Half-Shaft: Employ complete axles with a half-shaft from a ’94-01 Integra or ’99-00 Civic Si.
U.S. 96-01 Integra Engine Wire Harness: This is a mandatory component for this type of swap. A U.S. OBD2 Integra engine harness is designed to be backwards-compatible with OBD1 vehicles, simplifying the wiring process. Honda’s engineering cleverly made these harnesses adaptable for OBD1 chassis. Avoid using a JDM OBD2 Integra harness as it’s designed for right-hand drive vehicles, leading to significant wiring complications. Similarly, a U.S. OBD2 Civic engine harness is incompatible due to its one-piece design, unlike the two-piece design of OBD1 Civic/Integra and OBD2 Integra harnesses which allows for this backwards compatibility.
OBD1 ECU or OBD1-to-OBD2 Jumper Harness: You have two primary options for engine management:
1. Use an OBD1 ECU that corresponds to your engine type (e.g., OBD1 GSR ECU for an OBD2 GSR engine).
2. Utilize an OBD1-to-JDM OBD2a/b ECU jumper harness adapter to use a JDM or US OBD2 ECU.

ECU and Wiring Strategies for Your OBD2 Swap

The key to a successful OBD2 engine swap in your 95 EG Civic is the correct wiring and ECU setup. Using a U.S. OBD2 Integra engine harness significantly streamlines this process, eliminating the need to convert the OBD2 engine to OBD1 specifications. Remember, a JDM OBD2 Integra harness is not suitable for USDM vehicles due to right-hand drive configuration differences. Stick with a U.S. OBD2 Integra harness to avoid wiring headaches.

When installing the OBD2 Integra harness, you’ll notice some plugs won’t connect to your OBD1 vehicle’s main shock tower plugs. This is expected and won’t affect the engine’s operation.

Wiring Considerations for VTEC and JDM Engines

If you are installing an OBD2 VTEC engine into a non-VTEC OBD1 chassis, you will need to manually wire in components like VTEC, the knock sensor, and IAB (Intake Air Bypass) for GSR/SiR-G engines. Wire these components as you would for an OBD1 engine, using the same ECU pinout locations.

For JDM OBD2 engines, note that they typically lack a VTEC Pressure Switch (VTPS). You’ll need to address this for proper VTEC function in a USDM OBD1 car. You can either perform a wiring modification or replace the JDM VTEC Solenoid (VTS) with a USDM VTS.

VTPS Wiring Fix for JDM OBD2 Engines:

Splice the power wire for the VTPS into the VTS wire.
Ground the VTPS ground wire to the body of the VTEC Solenoid.

This simple fix prevents a Check Engine Light (CEL) for code 22 (VTPS) when using a USDM OBD1 ECU that expects a VTPS signal. If you opt for a JDM OBD2 ECU, this VTPS fix is unnecessary as JDM OBD2 ECUs do not monitor for a VTPS.

ECU Options: OBD1 vs OBD2

You have two primary paths for ECU management in your 95 EG OBD2 conversion:

OBD1 ECU (Recommended): The simplest and often best option is to use an OBD1 ECU appropriate for your OBD2 engine type. For example, for an OBD2 GSR engine, use an OBD1 GSR (P72) ECU. This ECU will plug directly into your existing OBD1 ECU plugs and control the engine. If a direct OBD1 equivalent ECU isn’t available for your specific engine (like an OBD1 ITR ECU), use a reprogrammable OBD1 ECU such as a chipped P28 ECU.
OBD2 ECU (Requires Jumper Harness): If you prefer to use an OBD2 ECU, it’s achievable but requires additional steps.
- OBD1-to-OBD2 Jumper Harness: Purchase an OBD1-to-OBD2a or OBD2b jumper harness adapter, depending on the OBD2 ECU type you choose.
- US OBD2 ECU Considerations: If using a U.S. OBD2 ECU, you’ll need to wire in a secondary O2 sensor and perform the “CKF (Crankshaft Fluctuation Sensor) Fix.” US OBD2 ECUs monitor these components, which may not be present or directly compatible with your OBD1 chassis.
- JDM OBD2 ECU Advantages: JDM OBD2 ECUs do not require a secondary O2 sensor or the CKF sensor fix, simplifying the installation if you choose this route.

While using an OBD2 ECU is possible, for a cleaner and often more straightforward conversion in a 95 EG Civic, opting for a compatible OBD1 ECU is generally the preferred method for many enthusiasts. This approach minimizes wiring modifications and potential sensor compatibility issues, making your OBD2 engine swap as seamless as possible.