Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

Camshaft Position Sensor (CMP)

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OPERATION



See Figure 1

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Fig. Fig. 1: Camshaft position sensor at the side of the camshaft support-Impreza

The CMP sensor located on the side camshaft support, or in the distributor, detects the number of pulses which occur when protrusions at the back of the camshaft drive sprocket cross the sensor.

The reference signal detected by the photoelectric CMP sensor are sent to the ECU. The ECU determines the optimum ignition timing from these signals and other engine operating parameters and transmits an ignition signal to the ignition coil igniter. The igniter amplifies the ignition signal and causes the primary current to flow intermittently in the ignition coil.

TESTING



Justy and Loyale

The CMP sensor in the distributor is not serviceable. The distributor should be replaced if the CMP sensor is found to be defective.

Except SVX
  1. Disconnect the CMP sensor connector.
  2.  
  3. Connect a voltmeter across the CMP sensor terminals.
  4.  
  5. Crank the engine. Voltage should vary around 0.1 volt alternating current and in time with engine movement.
  6.  
  7. If the CMP sensor tests satisfactorily, check the CMP sensor harness.
  8.  

SVX
  1. Remove the CMP sensor from the engine.
  2.  
  3. Connect a lab-type oscilloscope across the CMP terminals. Set the voltage scale to low level.
  4.  
  5. Wave a magnet past the CMP pickup area. The magnet should pass as close as possible without contacting the CMP sensor.
  6.  
  7. Examine the waveform on the oscilloscope as the magnet passes pickup. A waveform should appear as the magnet passes. If no waveform is present, replace the CMP sensor.
  8.  

REMOVAL & INSTALLATION



Justy and Loyale

The CMP in these models cannot be replaced independently. the entire distributor assembly most be replaced. Refer to the distributor removal and installation procedure in Engine Electrical for details.

Impreza
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the camshaft position sensor-to-camshaft support bolt.
  4.  
  5. Disconnect the electrical harness, and remove the camshaft position sensor from the engine.
  6.  

To install:
  1. Install the camshaft position sensor to the camshaft support and tighten the bolt to 36 ft. lbs. (49 Nm).
  2.  
  3. Connect the camshaft position sensor electrical harness.
  4.  
  5. Connect the negative battery cable.
  6.  

Legacy
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the timing belt.
  4.  
  5. Remove the left camshaft sprocket-to-camshaft bolt and the sprocket. Remove the left side-rear belt cover.
  6.  
  7. Remove the left camshaft support-to-cylinder head bolts.
  8.  
  9. Pull the camshaft support forward; be careful not to damage the camshaft position sensor wiring. Remove and discard the O-ring from the camshaft support.
  10.  
  11. Remove the camshaft position sensor-to-camshaft support bolt.
  12.  
  13. Disconnect the electrical harness and remove the camshaft position sensor from the engine.
  14.  

To install:
  1. Install a new O-ring into the camshaft support. Lubricate the camshaft support oil seal lips with grease.
  2.  
  3. Install the camshaft position sensor to the camshaft support, and tighten the bolt to 3.6 ft. lbs. (5 Nm).
  4.  
  5. Install the camshaft support to the cylinder head. Tighten the large bolt to 12 ft. lbs. (16 Nm) and the 2 smaller bolts to 7 ft. lbs. (10 Nm).
  6.  
  7. Install the camshaft sprocket, and tighten the sprocket-to-camshaft bolt to 47-54 ft. lbs. (64-74 Nm).
  8.  
  9. Install the timing belt.
  10.  
  11. Connect the camshaft position sensor electrical harness.
  12.  
  13. Connect the negative battery cable.
  14.  

SVX
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the timing belt.
  4.  
  5. Remove the left camshaft sprocket-to-camshaft bolt and the sprocket. Remove the left-side rear belt cover.
  6.  
  7. Remove the camshaft position sensor-to-cylinder head bolts.
  8.  
  9. Disconnect the electrical harness, and remove the camshaft position sensor from the engine.
  10.  

To install:
  1. Install the camshaft position sensor to the cylinder head, and tighten the bolts to 3.6 ft. lbs. (5 Nm).
  2.  
  3. Install the camshaft sprocket, and tighten the sprocket-to-camshaft bolt to 80-94 ft. lbs. (108-127 Nm).
  4.  
  5. Install the timing belt.
  6.  
  7. Connect the camshaft position sensor harness.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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