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NA6 Miata ECU Grounding

When installing a standalone ECU on an NA6, there is one step that is often overlooked and not well-documented. This step is to ensure that the car sensors are grounded to the ECU instead of the chassis.

Grounding sensors directly to the ECU rather than the chassis provides numerous benefits including reduced electrical noise, improved signal integrity, and better sensor performance. Eliminating factory ECU ground connections to the chassis becomes particularly important when swapping to a standalone ECU with additional sensors, as it ensures a centralized grounding system and avoids potential conflicts in sensor readings.


There is a stud coming off the intake manifold below the fuel rail, holding a P clamp for the wire harness with a connector to the Cam Angle Sensor. This is where a pair of grounds meet on a round ring terminal: one being a chassis ground (black), the other being an ECU ground (black and green). The black and green wire must be cut from this ring terminal and isolated. The location of this wire is shown in the images below:




Note: If your car's ground is different due to modifications, follow the harness from the passenger side firewall to the cam angle sensor, and the pair of grounds may have been relocated to another location. See the NA6 wiring diagram at the end of this guide for further information.


Sensor grounds play a critical role in ensuring accurate readings and proper functionality of various vehicle sensors. It is preferable to have sensor grounds connected to the ECU rather than the chassis. Eliminating a factory ECU ground connected to the chassis is important for several reasons:

  • Noise and Interference Reduction: Grounding sensors directly to the ECU helps minimize electrical noise and interference that can affect sensor signals. The ECU acts as a central point for grounding, providing a cleaner and more stable electrical reference for sensor operation.
  • Signal Integrity: Grounding sensors to the ECU ensures consistent and reliable signal integrity. By eliminating ground loops and potential differences between sensor grounds and the ECU ground, accuracy and precision in sensor readings are maintained, leading to more reliable engine management and diagnostics.
  • Improved Sensor Performance: Sensors rely on stable ground connections to function optimally. By grounding sensors to the ECU, they benefit from a more controlled electrical environment, resulting in improved sensor performance, responsiveness, and accuracy.
  • Preventing Ground Offset Issues: When sensors are grounded to the chassis, there can be voltage potential differences between the sensor ground and the ECU ground. This can lead to ground offset issues, where sensor readings are skewed or erratic due to voltage differentials. By grounding sensors directly to the ECU, these issues are minimized or eliminated. Maintaining Factory ECU Grounding: Factory ECU ground connections to the chassis should be eliminated if aftermarket modifications are made to the vehicle's electrical system. This ensures that sensor grounds are centralized and routed through the ECU, maintaining a consistent electrical reference and preventing potential conflicts or inconsistencies in sensor readings.

NA6 Wiring

If you are having difficulties tracing the correct wires to isolate, the wiring diagram below highlights the black and green ground wire and where it connects to on the car. By cutting the black and green wire from the engine block, you can see that the crank angle sensor is only wired to the ground on the ECU.