1994 GMC Safari Owner's Manual - Page 221

NOTICE: If you tryto do your own service work without knowing enough about it, your vehicle could damaged. be The 8th digit of your Vehicle Identification Number(VIN) shows the code letter for your engine. You will find the VIN atthe top left of your instrument panel. (See "Vehicle Identification Number"in the Index.) Use regular unleaded gasoline rated at 87 octane or higher. With the 4.3L (Code W) engine, use premium unleadedgasoline rated at 91 octane or higher for high power performance, when towing a trailer or with a high payload requirement. But when operating with a light load as a normal condition, you may use middle grade or regular unleaded gasolines. The gasoline you use should meet specifications ASTM D4814 in the U.S. and CGSB 35-92 in Canada. These fuels should have the proper additives, so you should not have to add anything to the fuel. In the U.S. and Canada, it's easy to be sure you get the right kind of gasoline (unleaded). You'll see "UNLEADED" right on the pump. And only unleaded nozzles will fit intoyour vehicle's filler neck. Be sure the posted octane is at least 91 for premium, 89 for middle grade and 87 for regular. 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 91 octane or higher and you still hear heavy knocking, your engine needs service. But don't worry if 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 it. It's the heavy, constant knock that means you have a problem. What about gasoline with blending materials that contain oxygen (oxygenates), such as MTBE or alcohol? MTBE is "methyl tertiary-butyl ether.'' Fuel that is nomore than 15% MTBE is fine foryour vehicle.