SMU - SEC. 6D IGNITION TIMING ADJUSTMENT PROCEDURE

SUBJECT: IGNITION TIMING ADJUSTMENT PROCEDURE

MODEL and YEAR: 1989-92 GEO PRIZM

This bulletin supersedes the ignition timing adjustment procedures found in the following service publications:

Section 6D4 of the 1989/90 Geo Prizm Service Manual (ST373-89/90)

Section 6D4 of the 1990-1/2 Geo Prizm Service Manual Supplement (ST373-90.5)

Section 6D4 of the 1990 Geo Prizm Service Manual Supplement covering the Prizm GSi Model (ST373-90 SUPP)

Section 6D4-A and Section 6D4-B of the 1991 and 1992 Geo Prizm Service Manuals (ST373-91 and ST373-92)

Refer to this bulletin when ignition timing adjustment becomes necessary.

Ignition Timing Adjustment - Tool Required: J 34186 Self Powered Inductive Timing Light

IMPORTANT: * In order to obtain an accurate engine idle speed and timing adjustment, the following vehicle conditions must be met:

- Air cleaner (ACL) and air intake duct are installed correctly.

- All electrical connections secure in their respective connectors.

- Vehicle wheels blocked with the transaxle in neutral.

- All vacuum hoses & connections free of leaks.

- All accessories and electrical loads turned off.

- Engine running at normal operating temp.

1. Open the diagnosis check connector cap and connect a tachometer to the battery and to the diagnosis check connector "IG" terminal (Figure 1).

NOTICE: DO NOT ground the diagnosis check connector "IG" terminal. Grounding this terminal could result in damage to the igniter or the ignition coil.

NOTICE: Make certain that the tachometer is compatible with this ignition system before installation. incompatible equipment installation could cause damage to the ignition system.

2. Install a jumper wire between terminal "T" (early production 1990 models) or terminal "TE1" (late production 1990 models and all 1991 and 1992 models) and terminal "E1" in the diagnosis check connector (Figure 2).

3. Run the engine at 2500 rpm for two minutes.

4. Return the engine to idle speed and adjust the throttle body screw until the correct engine idle speed has been obtained on the tachometer. Refer to the Vehicle Emissions Control Information Label under the hood for the correct idle speed specification.

5. Turn the ignition switch to "LOCK" and connect the inductive pickup lead of the J 34186 to the number one spark plug wire.

6. Connect the J 34186 power leads according to the manufacturer's instructions.

7. Start the engine and aim the J 34186 at the engine timing mark. The notch on the crankshaft pulley should line up at 10 degrees before top dead center (BTDC) on the timing indicator at each flash of the J 34186 (Figure 3). If an adjustment is required, loosen the distributor mounting bolts and slowly rotate the distributor while observing the timing indicator with the J 34186. Rotate the distributor until a reading of 10 degrees BTDC has been obtained.

Tighten

* Distributor mounting bolts to 20 N.m (15 lb. ft.)

8. Recheck ignition timing and adjust if required.

9. Remove the tachometer from the battery and diagnosis check connector "IG" terminal.

10. Remove the jumper wire from the diagnosis check connector and close the cap. Recheck ignition timing. Ignition timing should be varying between 0 and 20 degrees BTDC (Figure 4). Adjust as required.

11. Turn the ignition switch to "LOCK" and remove the J 34186 from the number one spark plug wire.

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.