A knock sensor is a piezoelectric sensor bolted to the block. When the engine knocks, the vibration makes the sensor produce a small voltage signal. The Nexus reads that signal and can pull timing through knock control. Because the signal is small, the wiring matters as much as the sensor.
How we wire it
- Use twin-core shielded cable from the sensor to the ECU's knock input.
- Ground the shield at one end only, at battery ground. Grounding both ends creates a loop that picks up noise.
- Route it away from ignition leads, coils and injector wiring where you can.
- Torque the sensor to spec on a clean, flat mounting face. A loose sensor gives a poor signal.
Assign the input in NSP on the knock wiring page. Some Nexus ECUs share the knock input with an SPI. The Nexus T1 and T2, for example, use SPI 2, so check that nothing else needs that input.
For sensors, the genuine Bosch knock sensor is our usual pick, and LS owners on a Nexus Rebel LS can use the Gen III knock sensor adaptor. Once it's wired, set up knock detection and the knock threshold.
