Ford 1996 Crown Victoria Manual page 308

Motorcraft Parts
If a spark plug is removed for examination, it
must be reinstalled in the same cylinder.
For 4.6L (2V) engines:
Cylinders #1, #2, #3, #4 have a PG suffix.
Cylinders #5, #6, #7, #8 have a P suffix.
If a spark plug needs to be replaced, use only
spark plugs with the service number suffix letter
as shown on the engine decal.
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