UPDATE-IGNITION TIMING ADJUSTMENT PROCEDURE

Models Affected: 1988-90 LEMANS WITH 1.6 AND 2.0

SERVICE MANUAL UPDATE

This bulletin cancels and supersedes the ignition timing procedure found on page 3 in Section 6D4.

The following is the correct procedure for both the 1.6L and 2.0L engines.

PROCEDURE:

---------- IGNITION TIMING ADJUSTMENT --------------------------

1.6L or 2.0L engines

1. Apply parking brake, block wheels and run engine at normal idle with the air conditioning off.

2. Verify that the "SERVICE ENGINE SOON" telltale lamp is not illuminated.

3. Ground the ALDL connector. The ALDL connector is located behind a small cover plate in the right kick panel. To ground the terminal, connect a jumper wire between the 2 left, lower-most cavities on the connector.

IMPORTANT: ---------- Grounding the ALDL connector causes the ignition timing control to shift from the ECM to the HEI module. This is known as Base Timing. The ECM cannot correctly control normal ignition timing unless the Base Timing is adjusted properly; this procedure is designed to adjust the Base Timing.

The "SERVICE ENGINE SOON" lamp should begin flashing when the ALDL connector is grounded.

4. There are 2 options for the timing light hook-up; connect the inductive timing pick up to either the coil wire, or to the #1 and #4 spark plug wires, respectively.

A. With the timing light connected to the coil wire, check for movement of the timing mark on the crankshaft pulley. The average or "middle" of the marks' movement should be 8 degrees BTDC.

B. With the timing light inductive pick up connected to the spark plug wires, check the position of the crankshaft pulley timing mark on the # 1 and 4 cylinders. The position of the marks should average out to be 8 degrees BTDC.

5. To adjust the timing, rotate the distributor slightly: turn clockwise to advance timing; counter clockwise to retard timing. Loosen the distributor mounting bolts to rotate the distributor (2 bolts on the 2.0L, 1 bolt on the 1.6L engine). Tighten the bolts when the ignition timing is within specification.

6. Remove the jumper wire from the ALDL connector. Verify that the "SERVICE ENGINE SOON" lamp stops flashing.

IMPORTANT: ---------- The 1.6L engine also has a magnetic timing probe socket, located just below the oil filter, Use the same procedure as with the timing light, except the timing should be set at 10 degrees BTDC.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.