Ford Town Car 2009 Owner's Manual page 266

Maintenance and Specifications
equivalent replacement parts. The customer warranty may be
void for any damage to the emissions system if such a PCV valve
is not used.
3
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.
266
2009 Town Car (tow)
Owners Guide, 1st Printing
USA (fus)