Test Procedures GMC Sierra 1500

The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following

1. With the ignition OFF, install a scan tool to the DLC.
2. Start the engine and bring to normal operating temperature IMPORTANT: Cam retard offset reading will not be accurate below 1,000 RPM
3. Increase engine speed to 1,000 RPM.
4. Monitor the cam retard offset.
5. If the cam retard indicates a value of 0° ± 2°, the distributor is properly adjusted
6. If the cam retard does not indicate 0° ± 2°, the distributor must be adjusted.

Scheme 6

1. With the engine OFF, slightly loosen the distributor hold down bolt. IMPORTANT: Cam retard offset reading will not be accurate below 1,000 RPM
2. Start the engine and raise engine speed to 1,000 RPM.
3. Using a scan tool monitor cam retard offset.
4. Rotate the distributor as follows: To compensate for a negative reading, rotate the distributor in the counterclockwise direction. To compensate for a positive reading, rotate the distributor in the clockwise direction.
5. Repeat step 4 until 0° ±2° is obtained
6. Turn the ignition OFF
7. Tighten the distributor hold-down bolt.
8. Start the engine.
9. Raise the engine speed to 1,000 RPM and recheck camshaft retard offset