Jeep Cherokee Forum

Jeep Cherokee 1987-1990: How to Replace Knock Sensor

The knock sensor is in place to detect and signal to the ECM of any ping or knock that occurs in the engine. A broken or failed knock sensor can result in poor engine performance and possible engine damage.

By Joseph Coelho - September 21, 2015

This article applies to the XJ Jeep Cherokee (1987-1990).

A knock sensor is a small piezoelectric device that can detect the frequencies associated with engine knock or detonation. Fitted to Jeep XJ models equipped with Renix fuel injection systems, the knock sensor will signal to the ECM when engine pinging/knocking occurs to allow for ignition timing adjustments to be made in an attempt to cure the problem. A vehicle operating with a malfunctioning or broken knock sensor can often lack performance and suffer from severe engine damage if the issue is left untreated. Individuals who regularly wrench on their XJ or take it off-road can easily break the vulnerable knock sensor, protruding out the side of the engine block. Fortunately, the knock sensor is easily accessed and can be quickly replaced to keep your Jeep running at its best. This article will outline the procedure for replacing the knock sensor on the 1987 to 1990 XJ Jeep Cherokee.

Materials Needed

  • Metric wrench set
  • Floor jack and jack stands (optional)
  • New knock sensor (Napa Echlin part #: DKS111)
  • Inch-pound torque wrench

Only 1987 to 1990 XJ Jeep Cherokee engines equipped with a Renix fuel injection system have a knock sensor. All other XJ engine configurations do not utilize a knock sensor.

Step 1 – Locate and remove knock sensor

  • The knock sensor is located on the driver's side of the engine block, just aft of the motor mount. It is best accessed from the underside of the vehicle. Depending on the suspension modifications, tire size, and general ride height of your XJ, lifting the vehicle and supporting it with jack stands may be necessary for easiest access to the sensor. (Related Article: How to Jack Up Your Car - CherokeeForum.com)
  • Remove the two prong electrical plug from the sensor. Inspect the plug for damage and replace if necessary.
  • Using the appropriate size metric wrench, unscrew the old knock sensor and remove it from the engine block.
Figure 1. Knock sensor location.

Pro Tip

Determining the correct knock sensor at a local parts house can be a bit difficult; however, many auto part stores can order or cross reference the Echlin part number provided above.

Step 2 – Install new knock sensor

  • Do not worry if your new knock sensor looks completely different from your old one. Several design changes have been made over the years and the original knock sensor has been superseded by improved sensors that vary in design.
  • Thread the new knock sensor into the engine block. It is important to not over-tighten the delicate sensor. Torque to 89 in/lbs (7.5 ft/lbs).
  • With the new sensor in place, reconnect the electrical plug.
  • Lower the vehicle off of jack stands if lifting was required.
Figure 2. Original knock sensor.

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