This sensor generates a signal when the engine is detonating. It does this using a piezo-electric element which generates a voltage when vibrated. The logic module monitors this voltage and considers it to be engine detonation when the voltage is above 0.8V at 2,000 rpm or above 4.0V at 4,000 rpm.
The 1984 logic module will reduce the maximum advance ignition timing for all cylinders by 2 degrees when detonation occurs. If the detonation continues, the maximum advance is reduced again by 14 degrees. If the detonation stops after the timing has been reduced again, the 14 degrees of maximum advance is restored.
For all later model logic modules, the amount of timing taken away from the maximum, depends on the severity and persistence of the detonation. The logic module identifies which cylinder is detonating (using the ignition reference and sync pickup sensors) and only reduces timing for that cylinder. When the throttle is partially open and there is no boost generated by the turbo, the maximum advance timing is reduced by 4.2 degrees, up to a maximum for 8.2 degrees when detonation occurs. If the engine is in boost, 2.1 degrees, up to a maximum of 15 degrees is reduced. The logic module will also reduce boost when the engine detonates while in boost. If detonation occurs more than once every 5.5 seconds, boost is reduced until the MAP sensor output is reduced up to 8% of what it was. If detonation occurs more than once every 17 seconds, but less than once every 5.5 seconds, boost is reduced to a percentage, based on the frequency of detonation up to a maximum of 8%. If detonation occurs once every 18 seconds or more, there is no reduction in boost.
Only 1985 model logic modules diagnosed the detonation sensor. If the engine speed is above 5,000 rpm and the detonation sensor voltage output is not greater than 0.04V for 3 seconds, a fault code 17 is stored and the power loss light is turned on. If the sensor ever outputs more than 0.04V, the power loss light is turned off.
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Updated 12/17/2003.
Copyright © 1996-2003 Russ W. Knize.