I have a 2006 F250 5.4L. I was getting a noticeable misfire after not driving the truck for a while.
Mode 6 revealed that cylinder #8 was misfiring.

I took off the coil/boot and there was coolant on the tip of the boot and some at the bottom of the spark plug well.

I cleaned everything up and put everything back together and that took care of that problem when I started the car. I also stuck a wad of paper towel by the intake manifold nearest spark plug number 8 and tightened the manifold bolts down a little. Some of them were not as tight as others.

I went back today and started the vehicle and it has the same problem again!

I took a look at the paper towel and it was totally dry! There is no coolant around the top of the spark plug well - only in the bottom of it. Where is this coolant even coming from? There are no coolant lines near cylinder #8. Is this a head gasket leak? I have taken a look at the head gasket and that doesn't seem possible since the head gasket does not seal around the spark plug well at all as far as I can tell.

Anyone have any ideas?

 

Why don't you start by giving us some information on the truck you're talking about.

 

I've got a V10 with a coolant leak from the intake manifold crossover tube putting coolant in the spark plug weeks all down the passenger side, and it to developed a wicked misfire. Haven't yet determined whether the two are for sure related. Mostly posting here to follow and learn more.

 

Whoops. It's an f250 2006 5.4L gas.

 

Its sounds like a cracked intake manifold.

Take a look at this: 2004 F250 Intake Manifold Replacement

 

That's what I had initially thought but a uv light showed no coolant around the spark plug and the paper towels by the intake soaked up no coolant either.

 

Is there any way water could be getting in there? Leaking through the cowl or the hood gasket or something?

 

Might have a bad cop.

 

Hey, I think looking around the cowl was a good idea. I looked today and it rained today too but there was no water under the cowl and there was no water on the COP.

I replaced took the COP off and there was no water down in the well. I don't know why it was misfiring. I replaced the COP and that solved the problem. I still don't know where the water came from originally though. Maybe it was from snow melt and that got around the cowl somehow? Don't really know.