I have been dealing with a misfire issue for cylinder number 4 on my 1999 F150 4.6 liter V8 (265000 miles) continuously for the last month. Before this time, I would have to deal with it a couple of times a year for the last 4 or 5 years.

In the past, before this past month, I would pull the no. 4 spark plug boot off and blow the moisture out of the spark plug hole. The strange thing is that sometimes it blow out antifreeze, other times it blow out water(?). What the heck? I would then coat the inside of the boot with a little Dielectric grease and be good to go!

Well, that all changed in May of this year. My truck decided it wanted me to work on it every few days concerning the misfire.

First Fix: I found and fixed a leaking windshield washer connector that was (guess where!) over the no.4 spark plug hole.

Second Fix: So, I decide it was time to replace the heater hoses. Keep in mind I had read horror stories about removing these hoses. I was not looking forward to this at all. One of them was leaking a little at the connection on the firewall. Ended up replacing both heater hoses. In order to do this I took my throttle body assembly off of the intake manifold. This gave me a lot more room to access those god forbidden connectors on the hoses. Got them removed after about 10 minutes of swearing at Ford engineering. LOL!

I had rented the heater hose connector removal "tool" and it didn't work worth a damn! I ended up using a small flat blade screwdriver and breaking the tabs off of the connector and sliding it off the heater core pipes. They both slid right off! I was shocked to say the least.

I get the hoses replaced and while I was replacing the EGR valve back on the throttle body, I drop a bolt and it fall underneath the intake manifold! I am thinking no big thing, I'll just fish around for it with my magnetic pick up and get it back in no time. It wasn't that easy. After a few more cuss words (and sobbing) I was unable to pick it with magnetic pick up
tool.

Third Fix: It was, at that time that I decided to go ahead and pull the intake manifold off to retrieve the EGR valve bolt. I had wanted to replace the intake manifold gaskets for quite awhile due to the age of my truck and to head off any future unforeseen problems. That was the best decision I made that weekend. After pulling the intake manifold off, retrieved the EGR bolt, I noticed the gasket had blown it's seal around the water jacket port next to the spark plug hole for number 4. Ahah! Number four spark plug was getting hit with two leakages! Replaced both of the intake manifold gaskets. Reinstalled the intake manifold and everything else being extra careful not to drop a bolt again ()
Fired it up and it ran like a champ!

But WAIT, it's not that easy! Within a few days it started misfiring again! WTF!
I pull the boot off of no. 4 and it is dry! I did the same with the other boots on that side and all is good. What the heck???? So, I decide just for grins that I will check the drivers side spark plug boots. No. 8 and 7 were dry, and when I checked no. 6 there was moisture on the boot and in the spark plug hole. Again, how did that happen? There are no water ( antifreeze) sources on that side of the engine. The only thing I could think of is when I pulled the intake manifold off some of the antifreeze spilled out and trickled down the no. 6 spark plug hole. So anyway, I blew the hole out, dried the boot off and applied dielectric grease, then reinstalled the boot.
I checked no. 5 and it was dry. :-) Engine ran fine.

Fourth Issue: BUT Wait! There's more! AND it is still not over...yet...............After a couple of more days it starts misfiring AGAIN!?! So I decide to run diagnostics and everything checks out fine, no misfires, all systems are go! I pull out my voltage meter and again all systems check out fine! Coil packs even checked out to spec! They can't be, my
engine is not running well at all. I was thinking about selling my truck at that point.

So, I take a step back and think "What is the main issue I have been dealing with all of this time?" Misfires!

Ok, back to square one. I pull all of the spark plug boots off on the passenger side. Sure enough there was moisture down on the no.4 spark plug boot! I put a paper towel over the hole and blow it out with my air nozzle. I smell the paper towel and it is water (!) not antifreeze. Somehow, Rain is getting in under the rear of the hood and dripping down the firewall over (what else?) the no. 4 spark plug boot and hole. After a heavy thunderstorm this past weekend, I opened the hood and saw a few drops of water on the back of the firewall. So, I dried the boot off, blew the hole out again, applied dielectric grease not only on the inside of the boot, but all over the outside of the boot, too! Fired it up and ran great! No hesitation, no low grade misfiring. Engine ran great even after the horrendous thunder storm overnight this past weekend. Problem solved!

Don't know if any of you guys are aware of the weather news around Dallas or Texas lately, but we have had heavy rains and bad flooding here for the past month or so. I had to literally work on my truck in between storms on one Saturday.

To make a long story short. I had four issues causing my misfire problem:
1) Leaking Windshield washer connector - Fixed
2) Heater Hose connector leaking - Fixed
3) Intake manifold blown gasket seal - Fixed
4) Rain somehow working it's way under the hood. Still troubleshooting that one at the moment.

Thanks for reading! I hope this may help others in resolving their misfire issues!

David

 

There should be a seal across the front of the wiper cowl covering the back of the hood area

 

Checked the rear hood seal. It looks ok to me but I am going to keep an eye on it.

Thanks,
David

 

Thanks for the write up! We learned something!