So, you’re diving into the world of Honda engine swaps and considering an OBD1 conversion for your B-series engine? You’ve come to the right place. This guide provides a detailed walkthrough on how to navigate the B Series Obd2 To Obd1 conversion, specifically tailored for those seeking enhanced engine management and tuning capabilities. Whether you’re working on a 96-98 Civic, 99-00 Civic, or an OBD2 Integra, understanding the nuances of this conversion is crucial.
Before we get started, let’s decode some common acronyms to make things smoother:
- OBD2a: Refers to 1996-1998 Civic and 1996-1999 Integra models.
- OBD2b: Denotes 1999-2000 Civic and 2000-2001 Integra models.
- EWH: Engine Wire Harness.
- VTS: VTEC Solenoid.
- VTPS: VTEC Pressure Switch.
- KS: Knock Sensor.
- IACV: Idle Air Control Valve.
- Dizzy: Distributor.
- PnP: Plug and Play.
OBD1 Conversion for 96-98 Civics
Engine Installation
When swapping in a B16, B18, B20VTEC, or any B-series engine into your 96-98 Civic, ensure compatibility with engine mounts, shift linkage, and axles.
Mounts and Brackets
For 96-98 Civics, consider using 99-00 Si engine brackets for a seamless fit:
- Front transmission bracket
- Rear engine “T” bracket (99-00 Si or JDM EK4/9 “T” bracket is recommended over Integra “T” bracket)
- A/C bracket
- Left side (driver side) dual-post engine block mount (only if using a B18 engine)
Alternatively, 94-01 Integra brackets are also compatible:
- Front transmission bracket
- A/C bracket
To retain A/C, use a “P54” 94-97 Delsol DOHC VTEC or a CRV A/C bracket, designed for the smaller Civic A/C compressor.
Reuse your stock Civic brackets for compatibility with B-series engines:
- Top transmission mount
- Left side (driver side) dual-post bracket
Shift Linkage
For 96-00 EK chassis, a 99-00 Si or JDM EK4/9 shift linkage is highly recommended for optimal shifter centering. Integra shift linkages may cause the shift lever to sit too far back.
Axles
Compatible axles include those from:
- 94-01 Integra (all 5-speed models, JDM or US)
- 99-00 Si
- 94-97 DOHC Delsol
Once the engine is mounted, wiring is the next step.
Wiring: Part 1
For 96-98 Civics, you can reuse your existing Engine Wire Harness (EWH), especially if it’s from a 96-98 EX 5-speed model. Note that OBD1 EWHs are incompatible due to their 2-piece design, unlike the 1-piece design in all EK Civics. Also, OBD2a (96-98 Civic) and OBD2b (99-00 Civic) harnesses are not interchangeable.
OBD2a and OBD2b harnesses are similar but not interchangeable, highlighting differences crucial for engine swaps.
If starting with a non-VTEC Civic harness, modifications are necessary to support an OBD1 VTEC engine:
- Add VTEC wiring (VTS & VTPS)
- Wire in the Knock Sensor (KS)
- Perform the IACV mod (convert 3-wire IACV plug to 2-wire)
The IACV mod is essential as OBD1 engines and 96-00 5-speed EX/99-00 Si Civics use a 2-wire IACV.
Wiring diagram for 96-98 Civics, illustrating the connections relevant for OBD1 conversion.
Detailed wiring diagram focusing on the A-plug for 96-98 Civics, crucial for understanding OBD1 integration points.
For VTEC Civic (like 5-speed EX) owners, using the existing EWH simplifies the process as VTEC and KS wiring are already present. However, the 2nd 02 sensor wiring is part of the cabin harness in EX models, not the engine harness. This becomes relevant if using a US OBD2 ECU. For OBD1 ECUs, the 2nd 02 sensor is not required.
For non-VTEC Civic owners hesitant about wiring, using a 96-98 5-speed EX EWH is a recommended, compatible alternative. Ensure it’s a 5-speed EX harness, not an automatic, as automatic harnesses are wired differently and may prevent starting.
Wiring: Part 2
Further wiring adjustments are needed to integrate an OBD1 engine into an OBD2 Civic, focusing on distributor, injectors, alternator, IAT, and CKF sensor.
- Distributor Plug: Convert to OBD1 distributor plugs by splicing or use an OBD2 B-series VTEC distributor (96-00) for a plug-and-play solution.
- Injector Clips: Convert to OBD1 injector plugs by splicing or use OBD2 injectors (96-00 B-series or D-series) for plug-and-play. Alternatively, modify OBD2 injector clips by removing the blue cap and securing them with zip ties onto OBD1 injectors.
Visual guide on modifying OBD2 injector clips for OBD1 injectors, offering a cost-effective wiring solution.
- Alternator Plug: OBD1 alternators use a round plug, while OBD2 use a square plug. Options include splicing OBD1 plugs, using an OBD2 B-series alternator (96-01), or swapping the inner plug from an OBD2 alternator into an OBD1 alternator.
Comparison of OBD1 and OBD2 alternator plug types, essential for correct wiring during the conversion.
- IAT Sensor: OBD2 and OBD1 IAT sensor plugs differ. Either modify your intake arm for the OBD2 sensor or splice in an OBD1 IAT plug to use the OBD1 sensor located on the intake manifold runner.
- CKF Sensor (Crankshaft Position Sensor): For US OBD2 ECUs, a CKF sensor workaround is necessary. US OBD2 ECUs expect this sensor, unlike OBD1 and JDM OBD2 ECUs. The CKF bypass trick eliminates the need to upgrade to a US OBD2 oil pump with CKF sensor.
ECU Options
Choosing the right ECU is crucial for your OBD1 conversion. Here are your options, from easiest to most complex:
-
JDM OBD2 ECU (Easiest)
- Pros: Direct plug-and-play, no VTPS requirement.
- Cons: Limited OBD2 ECU upgrades, fails US smog tests, 115-120mph speed limiter.
-
OBD1 ECU Conversion via OBD2a to OBD1 Jumper Harness
- Pros: OBD1 ECUs are easily reprogrammable, no 2nd 02 & CKF sensor requirements, more forgiving than US OBD2 ECUs.
- Cons: Fails smog tests, VTPS wiring needed.
-
US OBD2 Spec ECUs
- Option 3a: 96-97 DOHC VTEC Delsol P30 ECU; 96-99 Integra P72/GSR ECU; or 96-98 P73/ITR ECU.
- Option 3b: Convert to OBD2b spec via OBD2a to OBD2b jumper harness and use a 99-00 Civic Si ECU.
- Pros: Can pass smog with CKF bypass in Integra or Civic Si chassis, potentially in B-series BAR’d Civics.
- Cons: 2nd 02 sensor must be wired and functional.
OBD1 Conversion for 99-00 Civics
Engine installation steps for 96-98 Civics are also applicable to 99-00 models.
Wiring: Part 1
Wiring for 99-00 Civics is similar to 96-98 but with slight differences. For non-VTEC 99-00 Civics converting to OBD1 VTEC:
- Add VTEC wiring.
- Wire in the Knock Sensor (KS).
- Perform IACV mod.
- Change distributor plug to a 99-00 Si, 96-98 Civic, or 96-01 Integra large-sized distributor plug.
The IACV mod remains the same, converting to a 2-wire system.
Wiring diagram for 99-00 Civics, highlighting the specific wiring considerations for OBD1 engine swaps.
Detailed wiring diagram focusing on the B-plug for 99-00 Civics, essential for understanding OBD1 integration points.
99-00 SOHC Civics use a smaller distributor plug, requiring a change to a 99-00 Si or 96-98 distributor plug when reusing the SOHC EWH. Switching to a 99-00 Si EWH is recommended, similar to using an EX harness in 96-98 Civics, but the 2nd 02 sensor wiring is in the cabin harness, needing manual wiring for US OBD2 ECUs.
Wiring: Part 2
Wiring information from the 96-98 Civic section applies to 99-00 models as well.
ECU Options
ECU options for 99-00 Civics include:
-
99-00 Si ECU (Easiest)
- Pros: Direct plug-and-play, compatible with US OBD2 scanners, potentially passes smog with CKF bypass.
- Cons: CKF bypass required, limited OBD2 ECU reprogramming, 2nd 02 sensor needed.
-
OBD1 ECU Conversion via OBD2b to OBD1 Jumper Harness
- Pros: OBD1 ECU benefits as mentioned for 96-98 Civics.
- Cons: Fails smog tests, VTPS wiring needed.
-
US OBD2b Spec ECUs
- Option 3a: 99-00 Si ECU; 00-01 Integra GSR or ITR ECU (requires immobilizer removal).
- Option 3b: Convert to OBD2b spec via OBD2a to OBD2b jumper harness and use a 99-00 Civic Si ECU.
- Pros: Smog compliance with CKF bypass.
- Cons: 2nd 02 sensor needed.
-
JDM OBD2 ECU via OBD2b to OBD2a Jumper Harness or JDM CTR (PCT) ECU (OBD2b PnP)
- Pros: Smog compliance with CKF bypass possible in some cases.
- Cons: OBD2b to OBD2a jumper needed, fails smog tests, 115-120mph speed limiter.
OBD2a/OBD2b Integra OBD1 Conversion
Engine Installation
Reuse existing engine brackets, mounts, axles, and shift linkage in 96-01 Integras.
Wiring
Reuse the existing EWH and follow the wiring guides for 96-98 Civics (for 96-99 Integras) or 99-00 Civics (for 00-01 Integras).
Alternatively, 96-01 Integras can use a US OBD1 engine wire harness due to their 2-piece harness design, which is backward compatible with OBD1 EWHs. Compatible OBD1 VTEC EWHs include:
- 94-95 Integra GSR
- 92-95 Civic Si/EX
- 93-95 DOHC Delsol
For non-VTEC Integras, ensure VTPS, VTS, and KS are wired from the ECU plugs to the shock tower plug.
ECU Options
Note: 96-01 OBD2 Integras have the 2nd 02 sensor integrated into the cabin harness, eliminating the need for manual wiring. 00-01 Integra ECUs have immobilizers that must be removed for swapping.
- (96-99 Integra) JDM OBD2 ECU: Direct plug-and-play. Same pros/cons as 96-98 Civic with JDM ECU.
- (00-01 Integra) JDM OBD2 ECU: OBD2b to OBD2a jumper needed. Same pros/cons as 96-98 Civic with JDM ECU.
- (96-01 Integra) OBD1 ECU Conversion: Same pros/cons as 96-00 Civic OBD1 conversion.
- (96-99 Integra) OBD2a US ECU: Plug-and-play. Same pros/cons as 96-98 Civic.
- (00-01 Integra) OBD2a US ECU: Same pros/cons as 99-00 Civic.
- (96-99 Integra) OBD2b US ECU: OBD2a to OBD2b jumper needed; 00-01 Integra ECU requires immobilizer removal.
- (00-01 Integra) OBD2b US ECU: 99-00 Si ECU is plug-and-play; pin A15 to A16 move for fuel pump operation if using 00-01 Integra ECU; immobilizer removal or bypass chip needed for 00-01 Integra ECU.
Conclusion
Converting from OBD2 to OBD1 for your B-series engine opens up significant tuning and engine management possibilities. While it involves careful wiring and ECU selection, this guide breaks down the process for 96-98 Civics, 99-00 Civics, and OBD2 Integras. By understanding the nuances of each model and ECU option, you can successfully perform this conversion and unlock the full potential of your B-series engine. Remember to prioritize accurate wiring and choose the ECU solution that best fits your performance goals and local emissions regulations.
