1993 GMC Sonoma Owner's Manual - Page 252

Fuel e m ii i The 8th digit ofyourVehicleIdentificationNumber(VIN)showsthecode letterforyourengine. You will find theVINatthetopleftofyourinstrument panel. (See "VehicleIdentificationNumber" in theIndex.) Useregularunleadedgasolineratedat 87 octane orhigher.Withthe 4.3L (Code W) engine,usepremiumunleadedgasolinerated at 91octaneor higherforhighpowerperformance,whentowingatrailer or withahigh payload requirement.Butwhenoperatingwithalightloadasanormal condition,youmayusemiddlegrade or regularunleadedgasolines. ASTM D4814 in the U.S. The gasoline you useshouldmeetspecifications andCGSB3.5-92inCanada.Thesefuelsshouldhavetheproperadditives, so you should not havetoaddanything to the fuel. In the U.S. and Canada,it'seasyto be sureyougettherightkindof gasoline(unleaded). You'll see UNLEADED right on thepump.Andonly unleaded nozzleswill fit intoyourvehicle'sfillerneck. Be sure the postedoctane is atleast 91forpremium, 89 formiddlegrade and 87 forregular. If theoctaneislessthan 87, you maygetaheavy knocking noisewhen you drive.Ifit's bad enough, it candamageyour engine. 6-4 +' If you try to do your own service wok without knowing enough- about your vehicle could be damaged. KO489