Only the 3.5L engine is equipped with a knock sensor(s). This engine has two knock sensors, one for the right bank of cylinders and one for the left. The sensors thread into the top of the cylinder block below the cylinder heads. When a sensor detects a knock or pining in one of the cylinders, it sends an input signal to the PCM. In response the PCM retards the timing by a scheduled amount. The knock sensor is a tuned piezoelectric crystal transducer.
Perform a basic knock sensor test as follows. To make this test you will need a timing light.
- Connect a timing light to the engine.
- Start the engine and allowing warm up sufficiently.
- Position the timing light toward the timing marks on the harmonic balancer.
- Locate the knock sensor(s).
- Using a suitable metallic tool, tap on the intake manifold or side of the engine block which ever is closest to the knock sensor. Do not strike hard or hit the sensor directly, light tapping should cause the knock sensor to react.
- If the knock sensor is working the ignition timing will begin to retard as you tap.
- If the timing does not change, you will need to check voltage at the knock sensor harness connector. Also make sure the connector is clean and making good connection.
- Set the voltmeter on the AC scale and run the engine at 3000 rpms. If the voltage reading is 0.3-3.0 volts, the sensor is OK.
REMOVAL & INSTALLATION
See Figure 1
Only the 3.5L engines are equipped with a knock sensor. This engine utilizes two sensors threaded into the cylinder block, directly below the intake manifold.
- Remove the intake manifold plenum and manifold as described in Engine & Engine Overhaul .
- Disconnect the wiring harness attached to the knock sensor(s).
- Using a crows foot socket, remove the knock sensor(s).
- Install the knock sensor(s) and tighten to 7 ft. lbs. (10 Nm).
Over or under tightening of the sensor will result in poor sensor performance, and possible improper spark control.
- Attach the electrical connector to the knock sensor.
- Install the intake manifold and plenum as described in Engine & Engine Overhaul .