I put gas in my 94 z28 and now my car backfires

What octane gas did you put in it? And was it a reliable dealer? Also what engine do you have in it?

I have the 5.7 LT1. I put in 87 octane a Shell dealer, but it was in an old part of a downtown area. It was probably not the best choice. I noticed it almost immediately and unfortunately I let my tank get lower than normal with about 2 gallons left and I had to stop there. I did add some STP gas treatment after I parked it for the night. It idles fine, but as soon as I give it some gas it when it starts to backfire. It never did This before.

Wait until you almost completely run out of gas then put in goodgas and see