Embarking on a Vr6 Obd1 To Obd2 Conversion can seem like a straightforward upgrade, but as many DIY mechanics discover, the devil is in the details. This article delves into the experience of one enthusiast tackling this conversion, highlighting potential pitfalls and troubleshooting steps, particularly focusing on wiring intricacies and sensor compatibility.
Parts Swapped for OBD2 Conversion
The journey began with gathering the necessary components to transition from OBD1 to OBD2. Key parts for this conversion typically include:
- OBD2 Mass Air Flow (MAF) sensor
- Intake boot
- Throttle body
- Intake manifold
- OBD2 Engine Control Unit (ECU) – in this case, a ’99 MK3 ECU
- Engine bay wiring harness (’98)
- Engine wiring harness (’98)
Initially, the secondary oxygen (O2) sensor was intentionally omitted for a simplified setup, focusing on getting the primary conversion running smoothly.
Sensor Plug Differences: O2 Sensor and Cam Position Sensor
During the parts swap, a crucial detail emerged: the difference in plug shapes for sensors between OBD1 and OBD2 systems. Specifically, the O2 sensor plugs transitioned from a square to a round shape. Despite the plug shape change, the underlying wire functionality remained consistent. Similarly, the Cam Position Sensor (CPS) also featured a change in plug shape from square to round in later models like the ’98. While the part number changed, no functional differences beyond the plug interface were identified for the CPS.
To address these plug compatibility issues, a practical workaround was employed: snipping the plugs from the original OBD1 harness and splicing them into the new OBD2 harness. This allowed for the retention of the correct sensor connections despite the harness mismatch.
Initial Run and Idle Issues
With the parts installed and wiring adjustments made, the VR6 engine successfully started. However, the initial startup revealed a ‘jumpy’ or erratic idle. This is a common symptom indicating potential issues with air intake, vacuum leaks, or sensor readings after such a conversion.
Radiator Fan Troubleshooting
A more pressing issue arose with the radiator cooling fans failing to activate. This is critical for preventing overheating, especially during stationary idling. Troubleshooting steps were taken to isolate the problem:
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Direct Fan Test: Bypassing the temperature sensor on the radiator by jumping the pins successfully activated both high and low fan speeds, confirming the fans themselves were functional and the wiring to them was intact. This test was successful regardless of the engine being on or off, indicating the fan motors and relays were operational.
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Coolant Sensor Test: Jumping the pins at the brown coolant temperature sensor on the coolant flange resulted in the high-speed fans running whenever the ignition key was turned on. This suggested the coolant sensor circuit and fan control were partially functional but not being triggered correctly under normal operating conditions.
These tests indicated that the fan system was capable of working but was not receiving the correct signals to activate automatically based on engine temperature or AC engagement. This pointed towards potential issues with sensor inputs to the ECU, wiring discrepancies, or missing connections in the newly installed OBD2 harness.
Unconnected Wires and Potential Missing Links
Further investigation of the engine bay harness near the fuse box revealed a single unconnected wire – a lilac and black wire with a single pin connector. Additionally, a plug near the ECU, present in the OBD2 harness but absent in the original OBD1 setup, was found with no corresponding connection point. The purpose and relevance of these unconnected elements remained unclear, adding to the complexity of diagnosing the fan issue.
Error Codes Pointing to Sensor Signals
Diagnostic efforts using an OBD2 scanner revealed error codes related to:
- MAF Signal Too High: This could be related to a faulty MAF sensor, wiring issues affecting the MAF signal, or even unmetered air entering the intake system.
- CPS Signal Implausible: This code, appearing after splicing the CPS plug, suggested a potential problem with the spliced connections. The initial suspicion was that standard crimp splices might not be providing a reliable enough connection for the CPS signal. The plan was to upgrade to gold-plated crimp connectors to ensure optimal signal conductivity and rule out connection issues.
Next Steps and Community Input
Resolving the radiator fan and idle issues is paramount before considering the VR6 OBD1 to OBD2 conversion complete and reliable for driving, especially in demanding conditions. Further troubleshooting steps should include:
- Thorough Wiring Harness Check: Re-examining the entire engine bay and engine wiring harnesses to identify any missed connections, incorrect pin placements, or damaged wires. Double-checking grounding points is also crucial.
- Sensor Signal Verification: Using a multimeter or oscilloscope to test the signals from the MAF, CPS, and coolant temperature sensors to the ECU. This can help determine if the sensors are functioning correctly and if the signals are reaching the ECU as expected.
- Vacuum Leak Detection: Performing a smoke test to identify any vacuum leaks in the intake manifold or associated hoses, which could contribute to the jumpy idle and potentially affect sensor readings.
- ECU Pinout Review: Consulting the ECU pinout diagrams for both the OBD1 and OBD2 systems to ensure all necessary connections are correctly mapped and that no essential signals are missing or misrouted.
Community input and shared experiences from others who have undertaken the VR6 OBD1 to OBD2 conversion are invaluable. Insights into common pitfalls, specific wiring challenges, and solutions for similar issues can significantly expedite the troubleshooting process and lead to a successful and reliable OBD2 upgrade. Addressing the fan issue and resolving the sensor-related error codes are critical steps towards achieving a fully functional and properly running VR6 engine after the OBD conversion.
