Vehicle, is a '98 E-150 Chateau 172,000 now.
Last summer the CEL came on, misfire in #4, engine showed no problems, ran great so I just chalked up to minor sensor glitch on an 18 year old vehicle.

Couple weeks ago she starts running like crap when it's damp out, rain/snow of soon after before the streets dry up. Wet/damp in the morning, missing badly, power low, dry in the afternoon and it would smooth out again.
Figured a bad wire, not looking forward to changing them on a mod motor especially in a van. Had the codes checked again and now it showed a misfire in 4 and 7. Hmm, they run off the same side of the coil pack so I figured it was the coil as the wires were changed by the previous owner just over 4 years ago but only have 30,000, done at a Ford dealer, motorcraft wires, autolite platnums.
So I changed the one coil pack, fired her up, no CEL, seemed smooth, so far so good, though slight misfire at higher rpm. Driving it around it didn't quite feel smooth but compared to before it was running good and no CEL....well that lasted maybe 20 minutes. Missing again but not as bad as before.
THRowing the 304 code again, figured from runningb ad the past couple weeks maybe it fouled or burnt up the plug.
Brought it to a very reputable garage, kinda know them too. Anyhow they found the plug boot for #4 was full of rust?!?!?!?! They changed both 4 and 7 (just in case) wires and plugs (been out of work and cant really afford the extra couple hours to change the rest of the plugs and wires).
Anyhow, she ran GREAT afterwards, floored it thru first and second and it just ripped thru them like a new car, tried lugging it down and easing on the throttle (to avoid a down shift) and she was smooth. Drove around 30 miles running some errands, next morning taking my son to school, perfect, going to pick him up in the afternoon, perfect. Stopped at a store, came out and she seemed to have a very slight miss puttering thru the parking lot, nahhhh just my imagination. Pulling out onto the road. the friggen misfire is back
WTF?!?!?!?!?!?!?!?
This time it is only half as bad, maybe a little less then half as bad as it was the week before changing the coil pack and (4,7) plug&wires.
How could it run like new for 45-50 miles then suddenly go into crap mode again? Code is p0304 again.

What else to look for?
I'm sorta thinking the injector? Maybe while it was running bad with the 'rusted' wire it fouled or gummed it up? Though again, seems odd it ran super great for a day then...poof, right back to misfiring.





BTW, in all pics #4 is on the left. INcluded pic of coil side of 4 and 7 also, strange it looks like the brass on #4 is starting to rust?!?!
The old coil itself was all clean and shinny inside.

 

Almost forgot, pic of the #4 plug boot cut away.
Strange since the contact is brass and there was only very slight surface rust on the nipple on the plug.
It's actually so mild (on the plug) it seems more like it just came from the wire, not the nipple itself rusting.

 

 

Your story seemed to be more rhetorical...I didn't really see much of a question in there.

 

Sorry, I was adding as much background info/details as possible rather then just ask "I changed plugs, wires and coil but still have a misfire in #4, what could cause it?".
Too many people do that then those responding need to keep asking questions back to get the details before answering.
Anyhow, that was the question, "after doing what I did, why would I still have P0304?"


That said, I found the problem, the wire wasn't fully seated on the plug. Having large hands I cant get them in those tight places and couldn't push it down hard enough, the boot was gripping the plug just a little too much and was acting like a spring, after about a day (after installing it) it pushed the contact in the boot off the top of the plug. Took the engine cover off and could hear it arcing in the boot. Tried pushing it down as best I could get my fingers on it, I could feel the clip hitting the plug but it wouldn't stay.
Took it off, thoroughly greased the inside of the boot with a Q-tip, it slid down and snapped on the plug with out a fight...this time.

 

If only all the misfire solutions were so simple, nice job finding the issue.

 

thanks.....now if only changing the plugs and wires on a mod motor in a van was as easy as the 289 in my Galaxie.
In the time it took to do just #4 I coulda changed all of them and been at the local burger place eating a chicago style hot dog.

 

It looks to me like water is getting in there. Have you checked for any water leaks near there?

 

Yeah, all dry up there and it's been raining a lot lately.
I'm guessing I must have really hit a puddle a while ago that got a lot of water up there, probably on a day I didn't drive enough to get the engine hot enough to cause it to evaporate. Probably also at a time it sat a while, long enough to stay wet enough to cause all that rust.
Sometimes, especially in summer she sits a week or so with just being driven in and out of the driveway, in the past almost 4.5 years I've put just under 20k on it