Spark plugs ignition coil
Misfires in cylinder 2 and 8, can I just
replace those spark plugs and coils or do I
have to replace all 8
I would replace all 8. If a couple are bad, the rest aren't far behind.
worn out spark plugs may be the reason the coils went so at bare minimum you should replace all the spark plugs and just the bad coils for now. But you need to make sure that the misfire is plug and coil and not an injection, crank sensor, ECM or vacuum issue.
How many miles on this vehicle? I would try just replacing the spark plugs and I would change all 8 of them out. If you end up having a bad coil or 2 then I would replace all 8 of those as well. When purchasing coils it is best to stick with Motorcraft coils from Ford as they are far more dependable than some of the aftermarket crap that is sold at the parts stores. Ford Motorcraft coils can be ordered on line as well as from www.tascaford.com at the discounted price of $48.33 each plus freight.
Also could be dirty or clogged fuel injectors or fuel system including low fuel pressure or clogged fuel filter, or low compression including blown head gaskets or burned valves or bad rings. As said above buy Ford Motorcraft, as the other coils are junk.
You really want all spark plugs to be in the same condition.
Looking for a Used Grand Marquis in your area?
CarGurus has 1,103 nationwide Grand Marquis listings starting at $950.
Search Mercury Grand Marquis Questions
Mercury Grand Marquis Experts
Related Models For Sale
Used Cars for Sale