GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Ignition Timing



Ignition timing can be set on the 2.0L (VIN M) engine and the 2.5L (VIN U) engine equipped with the HEI ignition system only. The 2.5L (VIN U) engine was only equipped with HEI in 1985-86. From 1987 on, the 2.5L (VIN U) engine was equipped with the Direct Ignition System (DIS) which is distributorless.

All other engines are distributorless. Accordingly, ignition timing is controlled by the computer control module (ECM/PCM) and is not adjustable.

If the following procedures vary from the Vehicle Emission Control Information (VECI) label located in the engine compartment, set the timing according to the procedure indicated on the VECI label.


See Figure 1

  1. Start the engine, set the parking brake and run the engine until at normal operating temperature. Keep all lights and accessories off.
  3. Stop the engine. Connect the red lead of a tachometer to the terminal of the coil labeled TACH and connect the black lead to a good ground.
  5. If a magnetic timing unit is available, insert the probe into the receptacle near the timing scale. If a magnetic timing unit is not available, connect a conventional power timing light to the No. 1 cylinder spark plug wire.
  7. Start the engine and allow it to idle.
  9. With the parking brake safely set, place the automatic transaxle in D or leave the manual transaxle in Neutral.
  11. Ground the ALDL connector under the dash by installing a jumper wire between the A and B terminals. The check engine light should begin flashing.
  13. Aim the timing light at the timing scale or read the magnetic timing unit. Record the reading.
  15. Repeat Steps 3-6 using the No. 4 spark plug wire. Record the reading.
  17. Use the average of the 2 readings to derive an average timing value.
  19. Loosen the distributor hold-down nuts so the distributor can be rotated.
  21. Using the average timing value, turn the distributor in the proper direction until the specified timing (according to the Vehicle Emission Control Information label) is reached.
  23. Tighten the hold-down nuts and recheck the timing values.
  25. Remove the jumper wire from the ALDL connector. To clear the ECM memory, disconnect the ECM harness from the positive battery pigtail for 10 seconds with the key in the OFF position.