My 09 f150 pulled a p0308 cylinder 8 misfire code the other day. it has 90,000 miles on it and idk what to look for. I have checked the coil and its fine. im replacing plugs tomarrow hoping that it but i needed some info. It did it after i left the car wash and i guned it and the light started blinking then went off later on so the next day i tried to see if it would do it again and sure enough it did it started shaking when i let go of gas and lost power but sometimes it work perfectly fine and drives completely normal. WHy does it keep pulling the code and acting weird then i try it some other time and its fine...

 

There's no way to tel if a COP (coil over plug) is good or bad just by looking at it. You're likely misfiring because of a bad COP.

 

i switched the coil pack 5 and 8 and it still showed the same code

 

i was trying to check the wire from the coil today to see if it was bad cause the light keeps going on and off. could it be one of my sensors?

 

Thats the way my old 04 F250 5.4 work truck acted when a COP was going out( had well over 100k when this started IIRC). It would run OK then fall on its face. It happened to 2-3 other COP's before I "persuaded" our shop to just change the rest of them out, I was tired of bringing my truck in for a loaner every 3-4 weeks. Welcome to FTE, lots of friendly, knowledgeable folks here

 

thanks you so you think all of them are going out since i switched 5 and 8

 

No, I'm not suggesting you buy all 8. You could, I suppose- if you wanted to. I was just relaying my personal experience. I had 3 go out over the course of 3'ish months. That doesn't mean it would happen to yours

 

ok thanks could it be the plug by any chance if that not the problem or could it b the engine

 

Id start with the COP and go from there. I doubt its the engine. Keep us posted with your findings

 

If the coil was bad the misfire would follow it.
I would check the spark plug, it probably got water in the well and cracked the ceramic. You will see a black line (carbon track).

 

0308 code
i went thru all the coils, new plugs, checked injectors and looking for wiring breaks. Finally bought a compression tester and discovered 50psi in number 8, while the rest of the cylinders ranged 140-150 psi. Save some time while you are checking coils etc and While you have the plugs out, do the compression test.
In the end decide to pull the heads as the engine had 225000 kilometres, gave me a chance to regrind all the valves and polish up the cams, check all the wiring around the engine, clean out the mouse nest, change out soft parts and generally clean out accumulated sludge.