Converting your BMW E36 from OBD2 to OBD1 can seem daunting, but with careful planning and execution, it’s a manageable project. This guide provides a detailed walkthrough of the process, outlining the necessary parts, potential challenges, and solutions.
Why Convert to OBD1?
The primary motivation for an Obd2 To Obd1 Conversion in a BMW E36 is the performance potential. The OBD1 M50 intake manifold offers superior airflow compared to its OBD2 counterpart, leading to noticeable power gains. Additionally, OBD1 systems are often favored for their tuning simplicity and flexibility.
Parts Required for OBD2 to OBD1 Conversion
A successful conversion requires gathering the correct parts. Here’s a comprehensive list:
- OBD1 Engine Harness: Sourced from a non-EWS (BMW anti-theft) vehicle like a 1994 325i.
- OBD1 ECU: A “red label” 413 ECU is recommended as it typically comes from non-EWS cars.
- OBD1 Chip: Programmed for your specific engine setup and modifications.
- OBD1 Intake Manifold: The cornerstone of the performance gains.
- OBD1 Fuel Rail: Necessary due to differences in fuel line routing and pressure regulator location.
- OBD1 Crank Position Sensor: Located on the timing cover, unlike the OBD2 sensor on the engine block.
- OBD1 Cam Position Sensor: Required for proper engine timing.
- OBD1 Knock Sensors (x2): Essential for detecting engine knock and adjusting timing accordingly.
- OBD1 Oxygen Sensor: OBD1 systems utilize a single pre-cat O2 sensor.
- OBD1 HFM (Hot Film Air Mass Meter): Measures airflow for fuel injection calculations.
- OBD1 Main Coolant Hose: Connects to the timing cover, heater core, and expansion tank.
- OBD1 Throttle Boot: Adapts to the OBD1 throttle body and intake manifold.
- OBD1 Throttle Body (Optional): Can be used with an adapter or replaced with an OBD1 unit.
- OBD1 Valve Cover and Coil Packs (Optional): Offers a cleaner wiring solution.
Conversion Challenges and Solutions
While conceptually straightforward, several nuances require attention:
Valve Cover and Coil Packs
OBD1 and OBD2 coil pack wiring entry points differ. You can modify your OBD2 valve cover or use an OBD1 valve cover with corresponding coil packs. Both options function with the OBD1 harness.
Vanos Solenoid Wiring
The OBD1 Vanos solenoid connector is longer. Extend the OBD2 wiring using BMW part #12-52-2-274-971 or use an OBD1 solenoid.
Coolant Pipe
Address the difference in coolant pipe connections with an adapter or by replacing the OBD2 timing cover with an OBD1 version.
Throttle Body
Use an adapter plate or extended gasket to mate the OBD2 throttle body to the OBD1 intake manifold, or utilize an OBD1 throttle body.
Coolant Temperature Sensor
Splice the OBD2 wiring or use a plug-and-play adapter for the OBD1 dual-sensor setup.
Fuel Lines
Significant modifications are required, including rerouting fuel lines and relocating the fuel pressure regulator to the OBD1 fuel rail.
PCV System
Adapt the OBD2 PCV system, use an OBD1 breather valve, or install a catch can.
EWS Delete
Disable the EWS system by cutting wire #66 (solid green or black/violet) in the ECU connector.
Power Distribution and Grounding
Relocate the power distribution box and carefully connect power and ground wires, ensuring proper identification.
Wiring Harness Preparation
Thoroughly label all connectors on the OBD1 harness using wiring diagrams for accurate installation.
Conclusion
Converting your BMW E36 from OBD2 to OBD1 is a rewarding process that unlocks performance potential and tuning flexibility. By meticulously following this guide and addressing the specific challenges outlined, you can successfully complete the conversion and enjoy the benefits of the OBD1 system. Remember to disconnect the negative battery terminal before performing any electrical work.
