1993 Pontiac Grand Am Owner's Manual - Page 202

If you're using fuel rated at 91 octane or higher and you still hear heavy knocking, your engine needs service. But don't worryif you hear a little pinging noise when you're accelerating or driving up a hill. That's normal and you don't have to buy a higher octane fuel to get rid of pinging. It's the heavy, constant knock that means you have a problem. 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 than15 % MTBE is fine for your vehicle. Ethanol is ethyl or grain alcohol. Properly-blended fuel that isno more than 1 % ethanol is fine for your 0 vehicle. Methanol is methyl or wood alcohol. I Fuel that is more than 5 % methanol is bad for your vehicle. Don't use it. It can corrode metal parts in your fuel system andalso damage plastic and rubber parts. That damage wouldn't be covered under your warranty. And evenat 5 % or less, there must be : .''cosolvents" and corrosion . . ' 'preventers in this fuel to help avoid these problems. Fuel Capacity: 15.2 U.S. Gallons (57.5L). Use unleaded fuel only. eo1