I did a search on the forums for "miss" and "misfire", but couldn't see anything that answered my specific question. I just got a 2005 F150 Lariat 4x4 super crew 5.4 on Thursday. On Sunday, I noticed what felt like a slight miss or stumble when coasting down the highway at about 60 mph. I switched the cruise control off, and it went away. As the day went on, I noticed that the "miss" would recur when coasting, and it got to where it would do it even with the cruise off.

On Monday, it was more of the same, and on Tuesday, it was a little more pronounced. This morning, it was like it was on Tuesday, but when I went out for lunch, it didn't do it.

There is no CEL on, and it's quite random with the exception that it NEVER does it under load or at idle...only when coasting. Any ideas what could be going on here? The fella I bought it from replaced the 2 piece MC plugs with the 1 piece Champions at about 93K miles. The truck has 118K miles now.

Thanks in advance for any help or advice!

 

Get your codes read anyway its probably pending or wait sooner or later you'll get a cel. Probably just a coil. Could be those awful Champion plugs. Pull the code find out what cylinder start by swapping the coil if the miss moves get a new one if it doesn't pull the plug and see what it looks like.

 

I'd be more inclined to think you have a bad injector. The 2005's were known for lousy injectors. You could try a fuel injector clean like Techron or BG-44 but I doubt it's going to help. A miss fire while coasting is usually associated with excess fuel getting into one or more combustion chambers causing an imbalance of power and you will read it as a miss.