Adjusting the timing on a GMC Sierra with a distributed ignition requires special tools and a working knowledge of engine mechanics. A GMC Sierra model with a distributorless ignition controlled by the onboard computer requires professional reprogramming. Adjusting the timing on a GMC Sierra gets you more horsepower and lower emissions.
Instructions
1. Locate the crankshaft pulley at the front of the engine and clean it off to expose the timing marks. Start the car and turn off any accessories such as climate control, lights and the radio. Allow the engine to idle until it reaches normal operating temperature.
2. Connect the timing light to the battery and then to the number one ignition wire. Locate the assembly line diagnostic link also called an ALDL and use a jump wire to connect the diagnostic terminal B to the ground terminal marked A. The ALDL is located under the left side of the instrument panel. Not all models of the GMC Sierra have an ALDL.
3. Point the timing light at the crankshaft pulley to verify the need for adjustment. Adjust the timing by loosening the distributor mounting bolts and turning the distributor until the crankshaft timing mark lines up with the middle line of the timing light.
4. Tighten the distributor mounting bolts and recheck the timing. Remove the jumper wire from the ALDL with the engine running. Turn the engine off and remove the tachometer and timing light. Reconnect the number one ignition wire.
Tips Warnings
Failing to adjust the ignition timing properly causes excess engine wear or permanent damage.
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