GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Ignition Timing



This applies to the 3.1L engine only.

The Vehicle Emission Control Information label is attached to the front, right-hand shock tower in the engine compartment. Follow all instructions on the label. However, if the label is missing or defaced making it unreadable, use the following procedures:

Make timing adjustment with engine at normal operating temperature and the air conditioning system, if so equipped, turned off.

  1. Set the parking brake and block the drive wheels. The vehicle should be in Neutral or Park. Check the Service Engine Soon light. It should not be lit. Set the IC (Ignition Control) in the bypass mode by grounding the bypass circuit.

The IC bypass circuit is a single tan wire with a black stripe and connector that breaks out from the engine harness located adjacent to the right hand shock tower.

  1. With the ignition off, connect an inductive type timing light to the number one spark plug lead. Find the timing marks on the indicator plate on the front of the engine just above and slightly to the side of the crankshaft pulley. Make sure this is clean and readable. If necessary, mark the timing mark at 10° BTDC with a dot of white paint or White Out®. There is a slot cut on the crankshaft pulley that should be dabbed with a spot of paint to ease in setting the timing.
  3. Start the engine and aim the timing light at the timing mark. The line of the balancer or pulley will line up at the timing mark. If a change is necessary, loosen the distributor hold-down clamp bolt at the base of the distributor slightly. While observing the mark with the timing light, slightly rotate the distributor until the line indicates the correct timing. Tighten the hold-down bolt to 25 ft. lbs. (34Nm).
  5. Turn off the engine and remove the timing light. Disconnect the Ignition Control (IC) bypass wire from ground and clear any trouble codes from the Electronic Control Module. Refer to Driveability and Emission Controls for a further explanation of codes.