GM Metro/Sprint 1985-1993 Repair Guide

Diagnosis and Testing

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IGNITION COIL TESTING



See Figures 1 and 2



Click image to see an enlarged view

Fig. Fig. 1: Measuring ignition coil voltage



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Fig. Fig. 2: Measuring ignition coil resistance

  1. Check for spark at each spark plug with a spark plug tester. If no spark is detected, proceed to Step 2. If spark is only detected on some spark plugs, check for a faulty distributor cap or rotor. Also check the spark plugs and wires. Replace as needed.
  2.  
  3. Check for voltage at the ignition coil positive terminal with a voltmeter. If battery voltage is detected, proceed to Step 3. If battery voltage is not detected, repair the open in the wiring between the battery and the ignition coil.
  4.  
  5. Disconnect the connector on the negative coil wire. Check ignition coil resistance. If resistance is within specification, proceed to Step 4. If resistance is not within specification, replace the coil.
    1. Measure the resistance between the positive and negative terminals. Resistance should be 1.08-1.32 ohms electronic ignition with knock control and 1.33-1.55 ohms for all others.
    2.  
    3. Measure the resistance between the positive/negative terminals and the coil high tension wire terminal. Resistance should be 11.6-15.8 kilo-ohms for electronic ignition with knock control and 10.7-14.5 kilo-ohms for all others.
    4.  

  6.  
  7. On Conventional and ESC ignitions, check the resistance of the noise filter and condenser with an ohmmeter. If the resistance is 2.0-2.5 ohms for both units, proceed to Step 5. If the resistance is not within specification, replace both units as a set.
  8.  
  9. On Conventional ignitions, check the continuity of the brown/white wire between the ignition coil negative terminal and the distributor. If continuity exists, replace the pick-up coil and igniter. If continuity does not exist, repair the open in the wire.
  10.  

KNOCK CONTROL SYSTEM TESTING



See Figure 3



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Fig. Fig. 3: Knock controller circuit diagram

  1. Start the engine and allow it to reach normal operating temperature.
  2.  
  3. Depress the accelerator pedal rapidly and race engine. The TURBO light should illuminate on the dash. If not, inspect the lamp wiring and the lamp.
  4.  
  5. Connect a tachometer and check for proper idle speed.
  6.  
  7. Connect a timing light and check for proper ignition timing.
  8.  
  9. Disconnect the check coupler of the igniter. If ignition timing changes, replace the, replace the knock sensor and recheck the timing.
  10.  

The check coupler is located near the knock controller and has gray/yellow lead wires.

  1. With the check coupler disconnected, disconnect the knock sensor wire at the coupler. If ignition timing does not retard, replace the igniter with knock controller.
  2.  
  3. With the knock sensor coupler disconnected, connect check coupler. If timing is not restored to normally quickly, replace the igniter with knock controller.
  4.  
  5. Repeat Step 6 with the check coupler disconnected and connecting the knock sensor coupler. If timing is not restored to normally quickly, replace the igniter with knock controller.
  6.  
  7. Reconnect each coupler and check to ensure that ignition timing is set to specification.
  8.  

CENTRIFUGAL ADVANCE TESTING



  1. Remove the distributor cap.
  2.  
  3. Rotate the rotor counter-clockwise.
  4.  
  5. Release rotor, it should spring back.
  6.  
  7. Replace distributor if centrifugal advance fails this test.
  8.  

VACUUM ADVANCE TESTING



  1. Remove the distributor cap.
  2.  
  3. Remove the vacuum hoses.
  4.  
  5. Connect a vacuum pump to the outside vacuum hose on the distributor.
  6.  
  7. Apply 15 in. Hg of vacuum, the pick-up coil should move.
  8.  
  9. Repeat the same test with the inside vacuum hose.
  10.  
  11. On electronic ignition with knock control, connect a regulated air source to the nipple at the small vacuum chamber on the advance unit. When air pressure is applied, the pick-up coil should move.
  12.  

Never apply more than 18 psi of air pressure to the advance unit.

  1. If the pick-up coil does not move replace the vacuum advance unit.
  2.  

PICK-UP COIL TESTING



See Figure 4



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Fig. Fig. 4: Measuring pick-up coil resistance

  1. Remove the dust cover from the module.
  2.  
  3. Disconnect the red and white wires from the module.
  4.  
  5. Connect an ohmmeter to the red and white wires and measure the generator resistance.
  6.  

Do not connect the ohmmeter in reverse as this will damage the pick-up coil and module.

  1. Pick-up coil resistance should be within 900-1100 ohms on electronic ignition with knock control and 130-190 ohms on all others. If not within specification, replace the pick-up coil.
  2.  

IGNITION MODULE TESTING



See Figure 5



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Fig. Fig. 5: Testing ignition module

Conventional Spark Control Ignition
  1. Remove the dust cover from the module.
  2.  
  3. Disconnect the red and white wires from the module.
  4.  
  5. Connect an ohmmeter, a bulb and a 12 volt battery as shown in the illustration.
  6.  
  7. Set the ohmmeter to the 1-10 ohm range.
  8.  
  9. Touch the negative probe to the red wire terminal and the positive probe to the white wire terminal.
  10.  

Do not connect the ohmmeter in reverse as this will damage the module.

  1. If the bulb is illuminated, the module is good.
  2.  

 
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