2005 GMC Sierra 1500 Pickup Owner's Manual - Page 402

Some gasolines that are not reformulated for low emissions may contain an octane-enhancing additive called methylcyclopentadienyl manganese tricarbonyl (MMT); ask the attendant where you buy gasoline whether the fuel contains MMT. General Motors does not recommend the use of such gasolines. Fuels containing MMT can reduce the life of spark plugs and the performance of the emission control system may be affected. The malfunction indicator lamp may turn on. If this occurs, return to your authorized GM dealer for service. If your vehicle has the 5.3L V8 engine (VIN Code Z only), you may use either regular unleaded gasoline or ethanol fuel containing up to 85% ethanol (E-85); also see Fuel on page 5-6. In all other engines, including the 5.3L V8 (VIN Code T), use only regular unleaded gasoline. Only vehicles that have the 5.3L V8 engine (VIN Code Z) may use 85% ethanol fuel (E-85). General Motors encourages the use of E-85 in vehicles that are designed to use it. The ethanol in E-85 is a "renewable" fuel, meaning it is made from renewable sources such as corn and other crops. Many service stations will not have an 85% ethanol fuel (E-85) pump available. The U. S. Department of Energy has an alternative fuels website (http://www.afdc.doe.gov/refueling_mapsite.shtml) that can help you find E-85 fuel. Those stations that do have E-85 should have a label indicating ethanol content. Do not use the fuel if the ethanol content is greater than 85%. Your vehicle may not operate properly if the ethanol content is greater than 85%. Fuel E-85 (85% Ethanol) The 8th digit of your vehicle identification number (VIN) shows the code letter or number that identifies your engine. You will find the VIN at the top left of the instrument panel. See Vehicle Identification Number (VIN) on page 5-120. 5-8