GMC 2006 Sierra - Manual (Page 418)

Gasoline
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 5-122.
If your vehicle has the 5.3L V8 engine (VIN Code Z),
you may use either regular unleaded gasoline or ethanol
fuel containing up to 85% ethanol (E85); also see
Fuel E85 (85% Ethanol) on page 5-8. In all other
gasoline engines, use only regular unleaded gasoline.
Gasoline Octane
For all vehicles, except those with the 6.0L V8 engine
(VIN Code N), use regular unleaded gasoline with a
posted octane rating of 87 or higher. If the octane rating is
less than 87, you may notice an audible knocking noise
when you drive, commonly referred to as spark knock.
If this occurs, use a gasoline rated at 87 octane or higher
as soon as possible. If you are using gasoline rated at
87 octane or higher and you hear heavy knocking, your
engine needs service.
If your vehicle has the 6.0L V8 engine (VIN Code N), use
premium unleaded gasoline with a posted octane rating
of 91 or higher. You may also use regular unleaded
gasoline rated at 87 octane or higher, but your vehicle’s
acceleration may be slightly reduced, and you may notice
a slight audible knocking noise, commonly referred to as
spark knock. If the octane is less than 87, you may notice
a heavy knocking noise when you drive. If this occurs,
use a gasoline rated at 87 octane or higher as soon as
possible. Otherwise, you might damage your engine.
If you are using gasoline rated at 87 octane or higher and
you hear heavy knocking, your engine needs service.
Gasoline Specifications
At a minimum, gasoline should meet ASTM
specification D 4814 in the United States or
CAN/CGSB-3.5 in Canada. Some gasolines
may contain an octane-enhancing additive called
methylcyclopentadienyl manganese tricarbonyl (MMT).
General Motors recommends against the use of
gasolines containing MMT. See Additives on page 5-7
for additional information.
5-6