Backfire. how do I adjust timing?

You need to disconnect the EST wire and then check the ignition timing if its within specs-

where is the est wire located and how do i check the specs? I am new to this so every detail helps. tahnks

Est wire is brown and I think is either under the passenger side dash inside the car pre 1996 or near distributor/coil in engine compartment. You will need a repair manual (or friend) with the specification sheet. Another option is to call the local GM repair shop and ask them very nicely to look it up for you. Have the year, make, model, engine type, and even the VIN Number (look at base of window from outside on driver's side to find VIN)handy in case they ask. Don't waste their time cuz they are really doing you a favor helping you. They will give you the timimg spec in degrees before top dead center (TDC). Then you are ready to set the timing. If you need help with that let us know.