Tools You Will Need:
9/16" (on most cars) Distributor wrench or a socket that has an elbow in it to fit under the distributor platter
Inductive Timing Lights are the best, any timing light will work
Rags, most times you have to wipe off the timing tab on the timing cover
Wrench to unbolt the battery terminals to rest your computers ECM codes
Rubber glove to protect your hand from getting shocked at the distributor cap
Directions:
1) Shut off your car, let it cool off for about 5-10 minutes with the hood up 2) Disconnect the EST (Electronic Spark Timing). It is over on the passenger side and is a brown wire with a black stripe on it. It's not hard to miss because it is should be sticking out the wiring harness and is a big clip about 2" long x 1/2" thick. 3) Hook up your timing light to the negative and positive terminals of your battery. Hook up the timing wire to the #1 spark plug wire. There should be a tag on your light's wire that has an arrow saying "Arrow Towards Plug" or something to that effect. Make sure all of the wires are well away from any belts! 4) Prepare the distributor to be moved by loosening off the distributor's hold-down clamp on the passenger side. You'll see the clamp pressing down on the base of the distributor, it looks like a "V". 5) Start your car. Your Check Engine Soon light should come on and stay on steady. This is normal, because this is your computer telling you that the EST circuit is open. 6) Aim the timing light at the front of your motor down towards the very bottom of your motor. You will see the harmonic balancer turning. If you can't find it, look for the timing mark coming off of the front of the timing cover, it is a tag that should have graduated marks starting at 8 and going to 0. The highest number should be an 8 or 10 (some engines will have pointers beyone 20* BTDC). This is called BTDC (Before Top Dead Center). Advancing the timing towards that direction is called "advancing the timing" whereas moving it away towards the smaller section would be "retarding the timing". 7) Look up on the underside of your hood. If your car has never been repainted you should see a sticker that will tell you what the stock timing should be set at. On most Chevy engines it is 6BTDC or 6 degrees "Before Top Dead Center". 8) If your timing is ATDC (After Top Dead Center) or past the 0 mark (on the right side of it) you need to advance your timing. Go to the passenger side of your car and with the rubber glove on turn the distributor cap a little bit COUNTER-clockwise. Go back and check where the timing mark is. If the mark is hard to see turn off your engine and wipe off the timing mark on the timing cover and wipe off the harmonic balancer where the line is on it and start your car. 9) Set your timing a few times, trying to get it to stay as close to the stock timing setting as you can. Once that is done, shut off your car and tighten down your distributor. 10) Take your car for a drive around the block. Stomp on the gas hard and listen for "ping". It will sound like your motor is rattling. If you hear it, back your timing off by turning your distributor CLOCKWISE a bit. "Ping" is a precursor to engine damage, you want to avoid "ping" or "pre-detonation" as much as possible. 11) After you've set your timing make sure that you reconnect your EST (Electronic Spark Timing) wire over on your passenger side and reset your computer because the EST code will remain in your computer's memory. The code for the EST is 42 so if you don't reset your codes and later on you check them remember that the EST means at some point the EST circuit was open (or the plug was unplugged with the car running). Reproduced with permission from GMperformance.org Edited By: betterthanyou, ircmaxell and 92SonomaST | 
