Knock Sensor: Testing and Inspection

Fig. 3 Detonation sensor location:

1. Connect a suitable timing light to engine.
2. Set parking brake. Start engine and position throttle on second step of fast idle cam (at least 1,200 RPM).
3. Using a suitable hand operated vacuum pump, apply 16 inches of vacuum to Spark Control Computer transducer.
4. Using a small metal object, tap lightly on the intake manifold near the detonation sensor, Fig. 3. At the same time, using timing light, look for a decrease in spark advance at the timing marks. The decrease is proportional to the strength and frequency of the tapping. 20° is the maximum timing decrease.
5. Kick engine down to normal idle speed and turn ignition Off. Remove timing light and vacuum pump.