2007 F150 Lariat with P0307 Error Code
 

My 2007 Ford F150 Lariat (5.4L) with 82k miles popped a P0307 (#7 misfire) code one chilly morning. It began stumbing and hesitating a bit between 25-35mph, and each time it occurred, the engine light would flash on and off. Hesitation clears and light goes steady. Cleared the code and didn't see problems again for a month...until the next cold day (freezing temps). Popped again and hesitation returned. Ford dealer wants $350+ to change plugs. I've read coils can also cause the issue. Not sure if I can do either myself. Any advice for best way to fix this without just throwing money and parts at the issue? Thank you.

You are overdue for plugs. They should have been changed at 60k. 350 bucks is a reasonable charge, expect more if they break any. YOU can help by putting a bottle of Techron in every tank of gas till you get the plugs changed, this will help loosen the carbon and minimize breakage.

I ended up buying the Lisle tool from Amazon ($58) just in case, along with 4 Motorcraft 515 plugs. I replaced plugs 5, 6, and 7. Starting with the one that was malfunctioning (7), I found it was barely hand tight. 5 and 6 took a lot to break loose, but were then fine. No screeching and none broke. Put nickel anti-seize on new plugs and dielectric on boot contact. All back together and problem is resolved - under an hour's work. Running much cleaner. I'll do the other 5 plugs later on down the road when I need to.

It is best to do them now. The interval is no longer 100k it is 60k for plugs. I have 40k on my second set. It makes it easier and less likely to break.

While it seemed to be OK initially, the first cold morning, it happened again. Wicked shimmy from the engine and missing. Engine light flashed, but was off by the time I got home. Couldn't get a reader on it. As the truck warmed up, problems went away. So I just ordered the other 4 plugs. Was hoping to wait until weather thawed and I had a warmer day to do it. But guess I'll have to do it in the cold. Still not sure what was going on, but hoping finishing the plugs off will correct it.

Finished the other 5 plugs. #4 was loose as well and the boot smelled burnt. So I replaced that too. Have driven a couple weeks now with no further problems. Glad it wasn't anything more serious. Thanks for the help.