Sudden rough engine at all speeds
 

Hi all, I am hoping someone can tell me the most likely failure mode for my '06 Grand Marquis (160K). I was traveling at speed (55-60) everything seeming fine when suddenly, with no prior symptoms, the engine began to run rough. Within less than a mile, before I could pull over, the check engine light came on. I pulled into a parking lot, pulled out my smart phone and launched my OBDII app (ain't technology great). Trouble code P0308 - cylinder 8 misfire.

With this vehicle, what is the most likely cause? Spark plug, spark plug wire, coil pack (if it has one)? In the three years I have had this beauty I have never had a lick of trouble. Other than changing fluids I haven't had to do anything under the hood.

Any assistance greatly appreciated.

Roy

Your Grand Marquis has a "coil-on-plug" type ignition, which means there are no ignition wires to fail.
I misfire would be from a bad spark plug or a bad coil on the #8 cylinder.
Looking from the front toward the firewall, #8 is on the right (driver's side), closest to the firewall.
I don't know how old the plugs are, but I would replace them all so you know EXACTLY what is in your engine and how long the plugs will last.
I use and recommend the BOSCH #9606, which is a fine-wire, Double-Iridium design that has a life span of 100,000 miles +
I got mine at RockAuto -- best price !!