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. Changing the u-joints in your gmc sierra is a good project for the do-it-yourselfer or home mechanic. the u-joints are located at each end of the drive. If your gmc sierra is running hot, whether it is over-heating or just running at a higher temperature, then it might be time to replace your thermostat. a. How to set the engine timing on a 1988 gmc truck. engine ignition timing governs the spark signal to the spark plugs for firing. the distributor, according. You may also like. how to choose the oil and fluids for a gmc sierra. how do i turn off the change oil light in a gmc 2002 sierra pickup? how to change the.