1997 GMC Sonoma Owner's Manual - Page 241

Adding Equipment to the Outside of Your Vehicle Things you might add to the outside of your vehicle can affect the airflow around it. This may cause wind noise and affect windshield washer performance. Check with your GM dealer before adding equipment to the outside of your vehicle. Fuel Use regular unleaded gasoline rated at 87 octane higher. or At a minimum, it should meet specifications ASTM D48 14 in the United States and CGSB 3.5-M93 in Canada. Improved gasoline specifications have been developedby the American Automobile Manufacturers Association (AAMA) for better vehicle performance and engine protection. Gasolines meeting the AAMA specification could provide improved driveability and emission control system protection compared to other gasolines. Be sure the posted octane is at least 87. If the octane is less than 87, you may get a heavy knocking noise when you drive. If it's bad enough, it can damage your engine. If you're using fuel rated at 87 octane orhigher and you still hear heavy knocking, your engine needs service. But don't worry if you hear a littlepinging noise when you're accelerating or drivingup a hill. That's normal, and you don't have to buy a higher octanefuel to get rid of pinging. It's the heavy, constant knock that means you have a problem. If your vehicle is certified to meet California Emission Standards (indicated on the underhood tune-up label), it is designed to operateon fuels that meet California specifications. If such fuels are not available in states adopting California emissions standards, your vehicle will operate satisfactorilyon fuels meeting federal specifications, but emission control system performance may be affected. The malfunction indicator lamp on your instrument panel may turn on and/or your vehicle may fail a smog-check test. If this occurs, return to your authorized GM dealer for diagnosisto determine the cause of failure. In the event it is determined that the cause of the condition is the type of fuels used, repairs may not be covered by your warranty. Some gasolines that are not reformulated for low emissions contain an octane-enhancing additive called methylcyclopentadienyl manganese tricarbonyl (MMT); ask your service station operator whether or not his fuel contains MMT. General Motors does not recommend the use of such gasolines. If fuels containingMMT are used, spark plug life may be reduced and your emission control system performance may be affected. The malfunction indicator lamp on your instrument panel may turn on. If this occurs, return to your authorized GM dealer forservice. 6-3