Knock Sensor: Testing and Inspection

Knock Sensor Location:

1. Start and warm the engine to operating temperature.
2. Connect a suitable timing light to cyl #1.
3. While watching the timing marks, lightly tap on the cylinder block with a hammer or wrench near each sensor.

^ The timing should retard at least 3° in conjunction with the tapping.

If the timing does not change:

a. Check that the knock sensor mounting bolt torque is within specification (engine cold, 15 - 18 ft. lbs.). CAREFULLY, loosen and retorque as necessary.

WARNING: Disconnect the battery ground strap. Limited space between the alternator electrical connection and the knock sensor mounting bolt may cause an accidental short between the two components.

b. The harness should be checked for continuity and proper routing, Refer to CHASSIS ELECTRICAL DIAGRAMS.
c. Verify that the terminals for the knock sensor harness connectors are of the same material. Replacement knock sensors have gold plated terminals. Earlier original equipment sensors have alloy plated terminals. If a knock sensor with gold terminals is installed, be sure to replace the matching harness connector with gold terminals.


OSCILLOSC0PE TEST

4. With the engine "OFF", disconnect the knock sensor harness connectors.
5. Connect the positive lead of an oscilloscope to terminal #1 and the negative lead to terminal #2 of the knock sensor I. Refer to scope manufacture instructions.
6. Start the engine and warm to operating temperature.

Oscilloscope Display:

7. Operate the engine at 5000 rpm and observe the scope pattern.
8. Repeat steps 5 - 8 for knock sensor II.
9. If the pattern does not appear similar to the example, replace the knock sensor.