Cadillac 1999 DeVille Owner's Manual page 274

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.
If your vehicle is certified to meet California Emission
Standards (indicated on the underhood emission control
label), it is designed to operate on fuels that meet
California specifications. If such fuels are not available
in states adopting California emissions standards, your
vehicle will operate satisfactorily on fuels meeting
federal specifications, but emission control system
performance may be affected. The malfunction indicator
lamp on your instrument panel may turn on and/or your
-
vehicle may fail a smog check test. (See "Malfunction
Indicator Lamp" in the Index.) If this occurs, return to
your authorized Cadillac dealer for diagnosis to
determine the cause of failure. In the event it is
determined that the cause of the condition is the type of
fuels used, repairs may not be covered by your warranty.
Some gasolines that are not reformulated for low
emissions may contain an octane
called methylcyclopentadienyl manganese tricarbonyl
(MMT); ask your service station operator whether or not
the fuel contains MMT. General Motors does not
recommend the use of such gasolines. If fuels containing
MMT are used, spark plug life may be reduced and your
emission control system performance may be affected.
6-4
-
enhancing additive
The malfunction indicator lamp on your instrument
panel may turn on. If this occurs, return to your
authorized Cadillac dealer for service.
To provide cleaner air, all gasolines in the United States
are now required to contain additives that will help
prevent deposits from forming in your engine and fuel
system, allowing your emission control system to
function properly. Therefore, you should not have to add
anything to the fuel. In addition, gasolines containing
oxygenates, such as ethers and ethanol, and
reformulated gasolines may be available in your area to
contribute to clean air. General Motors recommends that
you use these gasolines, particularly if they comply with
the specifications described earlier.
NOTICE:
Your vehicle was not designed for fuel that
contains methanol. 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.
yellowblue