GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

Inspection and Adjustment

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DIS AND C 3 I SYSTEMS



On vehicles equipped with either the Direct or Distributorless Ignition System (DIS) or the Computer Controlled Coil Ignition (C 3 I) system, timing advance and retard are accomplished through the ICM with the Electronic Spark Timing (EST) and Electronic Spark Control (ESC) circuitry. No ignition timing adjustment is required or possible.

HEI SYSTEM



Because your car has electronic ignition, you should use a timing light which has an inductive pick-up. This type of pick-up merely clamps around the No. 1 spark plug wire, eliminating any kind of adapter. Other types of timing lights may cause false timing readings when used with ignition systems.


CAUTION
NEVER use a timing light which requires piercing of the spark plug wire.

  1. Refer to the instructions listed on the emission control label inside the engine compartment. Follow all instructions on the label.
  2.  
  3. Locate the timing marks on the front of the engine and on the crankshaft balances.
  4.  
  5. Clean off the marks so that they are readable. Chalk or white paint on the balancer mark (line) and at the correct point on the timing scale will make the marks much easier to accurately align.
  6.  
  7. If specified on the emissions label, attach a tachometer to the engine according to the tachometer manufacturer's instructions.
  8.  

On 4-cylinder engines, the TACH terminal is at the brown wire connection at the ignition coil; on V6's, it is next to the BAT connector on the distributor cap.

  1. Attach a timing light according to the timing light manufacturer's instructions. Remember that the inductive pick-up is clamped around the No. 1 spark plug wire.
  2.  
  3. Check that all wiring is clear of the fan, then start the engine. Allow the engine to reach normal operating temperature.
  4.  
  5. Aim the timing light at the timing marks. The line on the crankshaft balancer should align the correct timing mark. If the line is within 1° of where it should be, no adjustment is necessary.
  6.  
  7. If adjustment is necessary, loosen the distributor hold-down bolt slightly. Slowly rotate the distributor until the proper setting is attained.
  8.  
  9. Tighten the hold-down bolt, recheck the timing and readjust if required.
  10.  
  11. Turn the engine off and disconnect the timing light (and tachometer, if in use).
  12.  

Disregard the short tube which may be integral with the timing scale on some engines. This tube is used to connect magnetic timing equipment which is marketed to professional shops.

DIESEL



  1. Shut the engine OFF .
  2.  
  3. Note the relative position of the marks on the pump flange and either the pump intermediate adapter.
  4.  
  5. Loosen the nuts or bolts holding the pump to a point where the pump can just be rotated. You may need a wrench with a slight offset to clear the fuel return line.
  6.  
  7. Rotate the pump to the left to advance the timing and to the right to retard the timing. The width of the mark on the intermediate adaptor is about 2 / 3 °. Move the pump the amount that is needed and tighten the pump retaining nuts to 35 ft. lbs. (47 Nm).
  8.  
  9. Start the engine and recheck the timing as described earlier. Reset the timing if necessary.
  10.  
  11. Reset the fast and curb idle speeds.
  12.  

Wild needle fluctuations on the timing meter indicate a cylinder not firing properly. Correction of this condition must be made prior to adjusting the timing.

  1. If after resetting the timing, the timing marks are far apart and the engine still runs poorly, the dynamic timing could still be off. It is possible that a malfunctioning cylinder will cause incorrect timing. If this occurs, it is essential that timing be checked in cylinder 1 or 4. If different timing exists between cylinders, try both positions to determine which timing works best.
  2.  

 
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