Jeep Wagoneer/Commando/Cherokee 1984-1998

Knock Sensor

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OPERATION



The knock sensor is located on the lower left side of the cylinder block, just above the oil pan. The knock sensor provides and input to the ECU that indicates detonation (knock) during engine operation. When detonation occurs, the ECU retards the ignition timing advance to eliminate the detonation at the applicable cylinder.

TESTING



This procedure requires the use of a special tool M.S.1700, or an equivalent knock sensor tester.

  1. Connect diagnostic tester M.S.1700, or equivalent, to the vehicle according to the manufacturer's instructions.
  2.  
  3. Proceed to state display mode.
  4.  
  5. Start the engine.
  6.  
  7. Observe and note the knock unit value.
  8.  
  9. Using the tip of a screwdriver or a small hammer, gently tap on the cylinder block near the knock sensor and watch the knock value. The knock value should increase while tapping on the block.
  10.  
  11. If the knock value does not increase while tapping on the block, check the sensor connector. If the connection is good, replace the knock sensor.
  12.  

 
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