Service manual

90-898303 2-17

DETONATION CONTROL SYSTEM FUNCTION

1) Combustion noise (or vibration) excites the piezoelectric circuit located

inside the detonation sensor, which transmits a voltage to the control

module.

2) When cylinder number two ignition primary fires, it signals the controller to

look at a one millisecond window of sensor output, which it retains as a

reference level of combustion “background noise.”

3) When “background noise” reaches a measurable value, usually between

2500 and 3500 RPM (it is dependent on load), the ignition timing is

advanced 6 degrees beyond what the mechanical timing is set at. Timing

advance is accomplished by lowering the bias voltage.

4) The controller continues to monitor sensor output. If the output exceeds a

pre-determined threshold level over the “background noise” (which is

indicative knock is occurring) ignition timing is retarded by up to 8 degrees

and fuel flow is enriched by up to 15% until the sensor output is reduced

below the threshold level.

The detonation control system actually acts as an ignition advance module,

when knock occurs it takes away the advance. Ignition timing will not advance

if:

• Knock sensor fails.

• Blue/White wire becomes disconnected.

• Black wire has poor ground connection.

• Purple power wire becomes disconnected.

NOTE: Disconnected Gray/White wire will not affect ignition timing and will not

allow fuel enrichment.

Notes

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