Rover 820 Lucas Ignition

Knock Sensor

  • Purpose: To pick-up high frequency vibrations generated by pinking and pass the signal to ignition ECU which retards the spark timing.
  • Description: Piezo-Electric vibration transducer can be though of a a sensitive microphone exactly tuned to frequency band of noise generated by pinking.
  • Location: On the 16 Valve 820 is located in the centre of the rear side of the cylinder block, can be very difficult to get access to. Single cam carb equipped 820 models may have it located on the front of the block as on some Montego models.
  • Output Signal: Series of high frequency low (circa 0.7 V) Voltage peaks, will not show up on normal digital or analogue multimeter.
  • Connections & Pin Out.

    Two signal wires which connect to pins (1) and (3) of the Lucas AB17 Ignition ECU on the engine compartment  bulkhead and a grounded screen to  prevent radio frequency (RF) interference with the output.  On  820 16 valve engines the connection from the sensor to the ignition loom can be difficult to gain access to from above because of the inlet manifold, throttle body and starter however the output signal wires can be easily reached at the Ignition ECU where they are located near the top of the multiplug.  Wire piercing adapters (sold by Tandy) on the test equipment leads greatly simplify making the connection.
    Knock Sensor connections
    Vehicle Wiring Colour Code
    Ignition ECU Pin Number
    Light Green / Slate Grey trace
    1
    Slate Grey
    3

    Testing The Knock Sensor

    Test (1) Reaction of ECU to Knock Sensor Signal If you can't get a pass in the above test check the connections to the sensor also the condition of the wiring and that the sensor is tight in the threaded mounting boss on the block.

    Test (2) Checking Sensor Output

    For this test an oscilloscope is required although I have had results using a home made  low voltage (0 to 1.0 volt) tester I  use for measuring Lambda sensor output. A pass on Test (2) and Fail on Test (1) indicates an ECU or connection problem, a fail on both Tests (1) & (2) would indicate a sensor failure. Spurious trigering of the retard function of the ECU may be due to RF interence from the HT leads  so remember to check condition and grounding of the shielding on the sensor connecting cable.

    Test (3) Sensor Resistance

    Because of the very high impedance (30 million  Ohms) of the sensor this test is generally inconclusive, however if an oscilloscope is not available it may be of some diagnostic value if a suitable digital multimeter is available.

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