1993 Pontiac Firebird Owner's Manual - Page 219

Service & Appearance Care Be sure the posted octane for premiumis at least 91 (at least 89 for middle grade Use premium unleaded gasoline rated at 91 octane or higher. You may use middle and 87 for regular). If theoctane is less than 87, you may get a heavy knocking grade or regular unleaded gasolines, but noise when you drive. If it's bad enough, your vehicle may notaccelerate as well. it can damage your engine. The gasoline you use should meet specifications ASTM D4814 in the U.S. If you're using fuel rated at 91 octane or and CGSB 3.5-92 in Canada. These fuels higher and you still hear heavyknocking, should have the proper additives, so you your engine needs service. But don't should not have to add anything to the worry if you hear a little pinging noise fuel. when you're accelerating or driving up a hill. That's normal and you don't haveto In the U.S. and Canada, it's easyto be buy a higher octane fuel to get rid of sure you get the right kind of gasoline pinging. It's the heavy, constant knock (unleaded). You'll see UNLEADED right ,on the pump. And only unleaded nozzles that means you have a problem. will fit into your vehicle'sfiller neck, 218 5.7L LT1 (Code P) All Engines What about gasoline with blending materials that contain oxygen, such as MTBE or alcohol? MTBE is "methyl tertiary-butyl ether." Fuel that is no more than 15% MTBE is fine for your vehicle. Ethanol is ethyl or grain alcohol. Properly-blended fuel that is no more than 10% ethanol is fine for your vehicle.