GMC 1996 Sierra Owner's Manual page 252

Your vehicle has an air bag system. Before attempting to
do your own service work, see "Servicing Your Air
Bag-Equipped Vehicle" in the Index.
You should keep,a record with all parts receipts and list
the mileage and the date of any service work you
perform. See "Maintenance Record" in the Index.
You can be injured and your vehicle could be
damaged if you try to do service work on a
vehicle without knowing enough about it.
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Be sure you have sufficient knowledge,
experience, and the proper replacement
parts and tools before you attempt any
vehicle maintenance task.
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Be sure to use the proper nuts, bolts and
other' fasteners. "English" and "metric"
fasteners can be easily confused. If you use
the wrong fasteners, parts can later break
or fall off. You could be hurt.
Fuel (Gasoline Engine)
If your vehicle has a diesel engine, see "Diesel Fuel
Requirements and Fuel System" in the Diesel Engine
Supplement. For vehicles with gasoline engines, please
read-this.
Use regular unleaded gasoline rated at 87 octane
or higher. At a minimum, it should meet specifications
ASTM D4814 in the United States and CGSB 3.5-M93
in Canada. Improved gasoline specifications have
been developed by 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.
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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 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 pinging. It's the heavy, constant knock that means
you have a problem.
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