4000,S L4-1781cc 1.8L SOHC (MG) (1985)
Fig. 32 Ignition Map With Faulty Knock Sensor
Fig. 33 Ignition Map With Faulty Pressure Sensor or Throttle Switch
The control unit checks the knock sensor and its connections by measuring the background noises from the sensor which are present during normal
engine operation. If a fault develops in the sensor, the ignition timing will be constantly retarded to its 15° limit, Fig. 32. When this occurs, the
dashboard indicator light will come on.
The ignition control unit checks the operation of the pressure sensor and the throttle switches. If a problem develops in either of these components, the
ignition timing is retarded to a predetermined ignition curve Fig. 33, and the indicator light will come on.
If the ignition control unit fails, an electronic bypass in the control unit is switched on. The ignition timing then remains at the starting value of 6°
BTDC at all engine speeds, and the indicator light will come on.