GMC 1995 Jimmy Owner's Manual page 243

The gasoline you use should meet specifications ASTM D4814 in the
United States and CGSB 3.5-92 in Canada. These fuels should have the
proper additives, so you should not have to add anything to the fuel.
In the United States 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 into your 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 heavv.
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 no more than 15%
MTBE is fine for your vehicle.
Ethanol is ethyl or grain alcohol. Properly-blended fuel that is no more than
10% ethanol is fine for your vehicle.
Methanol is methyl or wood alcohol.
I
NOTICE:
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 and
also damage plastic and rubber parts. That damage wouldn't be
covered under your warranty. And even at 5% or less, there
must be "cosolvents" and corrosion preventers in this fuel to
help avoid these problems.
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