I have a 2003 4.6L 2wd Supercrew F150 with 150K miles....I replaced all 8 COP's prob. about 40K miles ago. About 3 weeks ago truck had a rough idle and engine light came on so went and had checked out at auto parts store and #3 cyl. misfire code came up so I just did a temporary fix and put in one of the old COP'S I had thrown in a box when I replaced the new ones and had been running fine since then. About 3 days ago, the check engine light came on again with #3 misfire so I put in another one....and now again last night the engine light came on again and its #3 engine misfire/running lean on scanner at auto parts store. Does anyone know why it would keep doing this day after day after day? Is it just old coil pack causing problem that was fine when I took them out or does anyone think it could be another problem....let me know your thoughts.

 

Pull the #3 plug and look at it - it may be bad. Are the plugs Motorcrafts?

What are the EXACT codes (by P-number) that the scanner picked up?

Could be a dirty fuel injector - throw some Techron in the tank.

 

Didnt get the exact code no. form the guy. The plugs have been replaced but when I was at the auto parts store last night I went ahead and bought 1 new Motorcraft plug to replace that #3 one and I am gonna try that also tonight. And I also put in a can of Seafoam last night.

 

I said Techron, not Seafoam........

 

I know.......I had already put a can of Seafoam in there before u mentioned the Techron. I put a new plug and coil pack in #3 and so far so good....we'll see.