Chrysler Front Wheel Drive Cars 4-CYL 1981-1995 Repair Information

Detonation (Knock) Sensor

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OPERATION



Chrysler Electronic Spark Control (ESC) System

The ESC system is used only on 2.2L carbureted engines.

The detonation sensor is tuned to the frequency characteristic of engine knocking ("spark knock'' or "ping''). When detonation occurs, the sensor sends a low voltage signal to the computer, which retards ignition timing in proportion to the strength and frequency of the signal. The maximum amount of retard is 20 degrees. When the detonation condition is no longer detected, the computer advances timing to the original value.

Chrysler Multi-Point Fuel Injection (MFI) System

The MFI system is used on 2.2L and 2.5L turbocharged and flex fuel engines.

EXCEPT 2.5L FLEX FUEL ENGINE

The detonation sensor is a device that generates a signal when spark knock occurs in the combustion chamber(s). It is mounted at a position on the intake manifold where detonation in each cylinder can be detected. The sensor provides information used by the engine controller to modify spark advance and boost schedules in order to eliminate detonation.

Eagle Throttle Body Fuel Injection (TBI) System

The Eagle TBI system is used only on 2.5L Premier engines.

The knock sensor is located on the passengers side engine mount just in front of the engine oil filter. It is threaded into a connector that is mounted to the engine block through the engine mount.

The knock sensor provides an input to the PCM that indicates detonation (knock) during engine operation. When detonation (knock) occurs, the PCM retards the ignition advance to eliminate the detonation (knock) at the applicable cylinders.

TESTING



Chrysler Electronic Spark Control (ESC) System
  1. Connect an adjustable timing light or magnetic timing unit light to engine.
  2.  
  3. Start engine and run it on second highest step of fast idle cam (at least 1200 rpm).
  4.  
  5. Connect an auxiliary vacuum supply to vacuum transducer and set on 16 in. Hg.
  6.  
  7. Tap lightly on the intake manifold near sensor with a small metal object.
  8.  
  9. Using the timing light, look for a decrease in spark advance. The amount of decrease in timing should be directly proportional to strength and frequency of tapping. The most decrease in timing will be 20 degrees.
  10.  
  11. If the sensor fails to perform as specified, replace the sensor and retest.
  12.  
  13. Turn ignition switch to OFF position and disconnect timing light.
  14.  

Chrysler Multi-Point Fuel Injection (MFI) System
EXCEPT 2.5L FLEX FUEL ENGINE

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: The detonation (knock) sensor on 2.5L Turbo I engines is located in the cylinder head between the center two fuel injector ports

A DRB scan tool is required for this test procedure. If a scan tool is not available, the test procedure for the ESC system can be used as a general procedure for this system as well; alter the procedure as needed.

  1. Connect Chrysler Diagnostic Readout Box (DRB II) or an equivalent scan tool to the diagnostic connector.
  2.  
  3. Place the scan tool into Sensor Test Mode to observe the knock sensor operation.
  4.  
  5. Warm the engine to normal operating temperature.
  6.  
  7. Raise the engine speed above 1000 rpm and using a metal object, lightly tap around the knock sensor. The scan tool should indicate knock is occurring. The DRB scan tool will do this by displaying an 8 in the readout box.

    If the scan tool is displaying a knock signal has occurred, the system is operating properly.
     
    If the scan tool is not displaying a knock signal, proceed to the next step.
     

  8.  
  9. Disconnect the electrical connector from the knock sensor.
  10.  
  11. Connect a jumper wire to the harness connector.
  12.  
  13. Raise the engine speed above 1000 rpm and momentarily touch the jumper wire to the positive battery terminal. The scan tool should indicate knock has occurred.

    If the system does not perform as indicated, the problem is not the knock sensor. Check the sensor wiring and the engine controller operation.
     
    If the system now indicates a knock signal, replace the knock sensor and retest.
     

  14.  

Eagle Throttle Body Fuel Injection (TBI) System

Direct testing of the knock sensor is not possible. To determine if the sensor is operating properly requires testing of various engine subsystems. Have the system tested by a qualified automotive technician.

REMOVAL & INSTALLATION



Chrysler Electronic Spark Control (ESC) and Multi-point Fuel Injection (MFI) Systems

EXCEPT 2.5L FLEX FUEL ENGINE

The detonation sensor is located in the cylinder head, behind the PCV breather/separator unit.

  1. Disconnect the negative battery cable.
  2.  
  3. Disengage the detonation sensor electrical wiring connector.
  4.  
  5. Use a wrench or socket and ratchet wrench to remove the detonation sensor from the cylinder head.
  6.  

To install:
  1. Apply anti-seizing compound to the sensor threads, then carefully start the sensor into the cylinder head by hand. Make sure that the sensor does not crossthread in the cylinder head.
  2.  
  3. Tighten the sensor until secure.
  4.  
  5. Attach the electrical connectors to the sensor.
  6.  
  7. Connect the negative battery cable.
  8.  

Eagle Throttle Body Fuel Injection (TBI) System

The detonation sensor is mounted in the engine mount, next to the oil filter.

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the detonation sensor electrical connector from the sensor.
  4.  
  5. Remove the detonation sensor from the adapter on the engine mount.
  6.  

To install:

WARNING
The installation torque is critical for detonation sensor operation. The sensor must be tightened to the correct torque to ensure proper operation.

  1. Install the knock sensor in the engine mount.
  2.  
  3. Tighten the sensor to 89 inch lbs. (10 Nm).
  4.  
  5. Attach the electrical connector to the sensor.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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