GM Cadillac 1967-1989 Repair Guide

Checking and Adjustment

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EXCEPT 4.1L, 4.5L AND 5.0L ENGINES



  1. Warm the engine to normal operating temperature. Shut off the engine and connect the timing light to the No. 1 spark plug (left front).
  2.  


WARNING
DO NOT, under any circumstances, pierce a spark plug wire to hook up the light. Once the insulation is broken, voltage will jump to the nearest ground, and the spark plug will not fire properly.

  1. Clean off the timing marks and mark the pulley or damper notch and the timing scale with white chalk or paint. The timing notch on the damper or pulley can be elusive. Bump the engine around with the starter or turn the crankshaft with a wrench on the front pulley bolt to get it to an accessible position.
  2.  
  3. Disconnect and plug the vacuum advance hose at the distributor, to prevent any distributor advance. The vacuum line is the rubber hose connected to the metal cone-shaped canister on the side of the distributor. A short screw, pencil, or a golf tee can be used to plug the hose.
  4.  

1981 and later models with Electronic Spark Timing have no vacuum advance, therefore you may skip the previous step, but you must disconnect the four terminal EST connector before proceeding.

  1. Start the engine and adjust the idle speed to that specified in the Tune-Up Specifications chart. Some cars require that the timing be set with the transmission in Neutral. You can disconnect the idle solenoid, if any, to get the speed down. Otherwise, adjust the idle speed screw. This is to prevent any centrifugal advance of timing in the distributor.
  2.  

On 1975-77 HEI systems, the tachometer connects to the TACH terminal on the distributor and to a ground. For 1978 and later models, all tachometer connections are to the TACH terminal. Some tachometers must connect to the TACH terminal and to the positive battery terminal. Some tachometers won't work at all with HEI. Consult the tachometer manufacturer if the instructions supplied with the unit do not give the proper connection.


WARNING
Never ground the HEI TACH terminal; serious system damage will result, including module burnout.

  1. Aim the timing light at the timing marks. Be careful not to touch the fan, which may appear to be standing still. Keep your clothes and hair, and timing light wires clear of the fan, belts, and pulleys. If the pulley or damper notch isn't aligned with the proper timing mark (see the Tune-Up Specifications chart), the timing will have to be adjusted.
  2.  

TDC or Top Dead Center corresponds to 0; B, or BTDC, or Before Top Dead Center, may be shown as BEFORE; A, or ATDC, or After Top Dead Center, may be shown as AFTER.

  1. Loosen the distributor base clamp locknut. You can buy special wrenches which make this task a lot easier.
  2.  
  3. Turn the distributor slowly to adjust the timing, holding it by the body and not the cap. Turn the distributor in the direction of rotor rotation (found in the Firing Order illustration) to retard, and against the direction to advance.
  4.  
  5. Tighten the locknut. Check the timing, in case the distributor moved as you tightened it.
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  7. Connect the distributor vacuum hose or engage the EST connector, as applicable. Check for the proper idle speed and, adjust as applicable.
  8.  
  9. Shut off the engine and disconnect the light.
  10.  

4.1L (V6) ENGINE



  1. Connect a timing light to the No. 1 spark plug wire according to the light manufacturer's instructions. DO NOT pierce the spark plug wire to connect the timing light.
  2.  
  3. Set the parking brake and position the transaxle in the PARK position.
  4.  
  5. Turn the ON and allow it to reach normal operating temperatures. Be sure the air cleaner is installed and the air conditioning turned OFF .
  6.  
  7. Inspect the instrument panel to be sure the CHECK ENGINE light is turned OFF .
  8.  
  9. Disconnect the 4-wire terminal connector from the distributor. See the Underhood sticker for identification. The CHECK ENGINE light will turn ON .
  10.  
  11. If necessary, loosen the distributor hold-down bolt and turn the distributor until the specified timing is obtained.
  12.  

All V6 engines harmonic balancers have 2 timing marks, 1 measuring1/8in. (3mm) wide and 1 measuring the normal

1 / 16 in. (1.5mm) wide. The smaller mark is used for setting the timing with a hand held timing light. The 1 / 8 in. (3mm) wide mark is required when using magnetic timing equipment. All engines have a mounting bracket on the front cover which will accept a magnetic timing pick-up probe.

  1. Tighten the mounting bolt and recheck timing to see if it changed during tightening.
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  3. Reconnect the electrical connector to the distributor.
  4.  
  5. Stop the engine, then, temporarily disconnect the negative battery terminal to cancel any stored trouble codes.
  6.  

4.1L AND 4.5L (V8) ENGINES



See Figure 1

The engine incorporates a magnetic timing probe hole for use with special electronic timing equipment. Consult manufacturer's instructions before using this system. The following procedure is for use with the HEI - EST distributor.

  1. Connect a timing light to the No. 1 spark plug wire according to the light manufacturer's instructions. DO NOT pierce the spark plug wire to connect the timing light.
  2.  
  3. Set the parking brake and position the transaxle in the PARK position.
  4.  
  5. Follow the instructions on the emission control label located in the engine compartment.
  6.  

DO NOT attempt to time the engine if it is operating on 7 cylinders for damage to the catalytic converter may occur.

  1. On the 4.5L (273 cu. in.) engine, connect a jumper wire between pins A (ground) and B of the Assembly Line Data Link (ALDL) connector (located near the parking brake pedal under the dash).
  2.  

By jumping the Assembly Line Data Link (ALDL) connector, the ECM will command the BCM to display a SET TIMING message on the Climate Control Driver Information Console (CCDIC). The engine will now operate at base timing. The timing can now be checked with a standard timing light at 10 degrees BTDC at 900 rpm or less.

  1. Start the engine and run it at idle speed until normal operating temperatures are reached.
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  3. Aim the timing light at the degree scale just over the harmonic balancer; the line on the pulley should align with the mark on the timing plate.
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  5. If necessary to adjust the timing, use the Distributor Wrench tool No. J-29791 or equivalent, to loosen the hold-down clamp, then, rotate the distributor until the desired ignition advance is achieved. When the correct timing is set, torque the hold-down clamp nut/bolt to 20 ft. lbs. (27 Nm).
  6.  

To advance the timing, rotate the distributor opposite the normal direction of rotor rotation. Retard the timing by rotating the distributor in the normal direction of rotor rotation.



Click image to see an enlarged view

Fig. Fig. 1: Jumping the ALDL connector in order to prevent advance while setting base ignition timing

5.0L (V8) ENGINE



See Figure 1

  1. Connect a timing light to the No. 1 spark plug wire according to the light manufacturer's instructions. DO NOT pierce the spark plug wire to connect the timing light.
  2.  
  3. Set the parking brake and position the transaxle in the PARK position.
  4.  
  5. Turn the engine ON and allow it to reach normal operating temperatures. Make sure the choke is FULLY OPEN and the air conditioning turned OFF . Connect a jumper wire between pins A (ground) and B of the Assembly Line Data Link (ALDL) connector (located near the parking brake pedal under the dash).
  6.  
  7. Aim the timing light at the timing plate. If necessary, loosen the distributor hold-down nut and rotate the distributor until the specified timing adjustment is obtained.
  8.  
  9. While the engine is still operating, remove the ground wire from the diagnostic terminal.
  10.  

If the ground wire is removed before the engine is turned OFF, no trouble codes will be stored.

  1. Remove the timing light.
  2.  

 
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