Chrysler Front Wheel Drive Cars 6-CYL 1988-1995 Repair Information

Crankshaft Position Sensor (CKPS)

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OPERATION



The non-Premier and Monaco 3.0L engines do not have a separate Crankshaft Position Sensor (CKPS). Those engines utilize a distributor pick-up for this purpose.

3.3L and 3.8L Engines

See Figures 1, 2 and 3

The Crankshaft Position Sensor (CKPS) perceives slots cut into the transaxle drive plate extension. There are 3 sets of slots, each set containing 4 slots, for a total of 122 slots. Basic timing is determined by the position of the last slot in each group. Once the engine computer (Powertrain Control Module-PCM) senses the last slot, it determines crankshaft position (which piston will next be at Top Dead Center/TDC) from the camshaft position sensor input. The 4 pulses generated by the CPS represent the 69°, 49°, 29°, and 9° Before Top Dead Center (BTDC) marks. It may take the PCM one engine revolution to determine crankshaft position during cranking.



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Fig. Fig. 1: Crankshaft Position Sensor (CKPS)



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Fig. Fig. 2: The CKPS timing slots found in the transaxle drive plate



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Fig. Fig. 3: The CKPS location and wiring connectors

The PCM uses the camshaft position sensor to determine fuel injector sequence. The PCM determines ignition timing from the CKPS. Once the crankshaft position has been determined, the PCM begins energizing the injectors in sequence.

The CKPS is located in the transaxle housing, above the vehicle speed sensor. The bottom of the sensor is positioned next to the drive plate.

The distance between the bottom of the sensor and the drive plate is critical to the operation of the system.

Early Premier and Monaco

See Figures 4, 5, 6 and 7

If you are not sure whether your Premier or Monaco is designated as an early or late model, please refer to the model differentiation portion of this section.

The CKPS in this vehicle is also the speed sensor. The speed sensor, attached to the torque converter drive plate housing, provides an input signal to the ECU relating to crankshaft angle (position). The ECU converts the rate of change of the crankshaft angle into engine RPM and the crankshaft angle to piston position. The speed sensor senses TDC, BTDC and engine speed by detecting the flywheel teeth as they pass during engine operation. The speed sensor is nonadjustable.

The drive plate pulse ring has three trigger notches, 120° apart. There are 20 small teeth (windows) between each trigger notch. Each large trigger notch is located 12 small teeth before TDC position of the corresponding pistons.



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Fig. Fig. 4: Crankshaft timing sensor



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Fig. Fig. 5: Crankshaft timing sensor location



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Fig. Fig. 6: CPS/engine speed sensor and trigger notches on the transaxle drive plate-Premier and Monaco (1988-90 and early 1991 models)



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Fig. Fig. 7: The notches in the flexplate affect the magnetic field generated by the CKPS, and this effect triggers the voltage pulses sent to the ECU-Premier and Monaco (1988-90 and early 1991 models)

When a tooth and notch pass the magnet core of the speed sensor, a voltage spike is induced in the sensor pick-up coil winding. The voltage spikes allow the ECU to count the teeth as they pass the sensor. When a trigger notch passes the speed sensor there is a longer than usual delay between voltage spikes. This longer delay tells the ECU that a piston will be at the TDC position 12 voltage spikes later. The ECU uses information from the speed sensor to control spark timing and fuel injection timing for each cylinder.

The longer voltage spike indicates to the ECU that a piston will soon be at the TDC position, 12 teeth later. The ignition timing for the particular cylinder is either advanced or retarded as necessary by the ECU according to sensor inputs.

Late Premier and Monaco

See Figures 4 and 5

If you are not sure whether your Premier or Monaco is designated as an early or late model, please refer to the model differentiation portion of this section.

The crankshaft timing sensor input is used by the SBEC to determine timing for the ignition system and fuel injector firing. The CKPS sensor senses four sets of slots (4 slots per set) cut into the transmission drive plate. Basic timing is set by the position of the last slot in each group. This is a fixed timing system with no means of adjustment.

TESTING



Except Early Premier and Monaco

For this procedure a dwell meter, or the equivalent, will be needed.

  1. Unplug the Crankshaft Position Sensor (CKPS) connector.
  2.  
  3. Turn the ignition ON .
  4.  
  5. Using a voltmeter, measure the voltage from the wiring harness connector 5-volt supply circuit (orange wire) to ground.
    1. If the voltage is 8-9.5 volts, skip to the next step.
    2.  
    3. If the voltage measured is lower than 8 volts, or higher than 9.5 volts, the CKPS is not receiving the correct current to function properly. There is a problem in the wiring or related components.
    4.  

  6.  
  7. Turn the ignition OFF .
  8.  
  9. Attach the CKPS wiring and engine wiring harness connectors back together.
  10.  
  11. Attach a dwell meter to the battery. Attach the lead probe of the dwell meter to the sensor signal wire (gray with black tracer) by backprobing the connector or by using jumper cables between the terminals.
  12.  
  13. Place the dwell meter out of the way of any mo