Mercury 2009 Grand Marquis - Page 256

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For spark plug replacement, see your authorized dealer. Refer to
scheduled maintenance information for the appropriate intervals for
changing the spark plugs.
Replace the spark plugs with ones that meet Ford material and
design specifications for your vehicle, such as Motorcraft or
equivalent replacement parts. The customer warranty may be
void for any damage to the engine if such spark plugs are not
used.
2009 Grand Marquis (grn)
Owners Guide (own2002), 2nd Printing
USA (fus)
Maintenance and Specifications
256