Ddawg 99 f.150 5.4

Hey guys I had an on going problem that happens every now and then. Well when it rains or I'm offroading or if i park it for a period of time when it's humid my truck starts skipping, misfiring and so on and the service engine soon light comes on then in about three days of driving it clears up and the light goes off. Is it just me or are my coils very sensitive? Truck is a 1999 5.4 spark plugs were changed 4 months ago. Any suggestions? Thanks, Clay.

Fordfan2006

one might be bad my 5.4 doesn't act up when wet but I was driving a 2006 5.4 and it was wet out and it acted like it wasn't going to start and acted like it was going to stall it turned out a coil was bad on it now it runs like new

Tackle

Make sure the rubber seal that goes between the hood and the firewall part is good and not missing. That would allow water to run in.

Who ever changed your plugs should have used more dielectric grease both in the boot and around the boot on the bottom. Makes a better seal and will keep water from causing the problems you're having.

Or you have one bad one (if it's always the same one when you scan the CEL).

If they are not Motocraft that could be part of the problem.

Ddawg 99 f.150 5.4

Oh alright it might be because it's got all the original coils and it has 120k but when's it's dry it runs great so I figured they just didn't like water so I guessed it was fine but I might just replace all 8 and call it a day

Ddawg 99 f.150 5.4

I changed the plugs myself and I used alot of dielectric grease in the boots and all the coils are original that I know of and it has 120k and there is a seal between the firewall and hood

Jbrew

Also can depend upon which plugs you used. Night and day. The housings also crack, that's usually from over tightening. Coils should remain movable on the bushings. You should be able to move them from side to side after a light spec torque. They should NEVER be tight. They will stress crack then suck that moisture right in.

Ddawg 99 f.150 5.4

I use just standard motorcraft plugs and I tighten the coils just hand tight and on a ford I use motorcraft everything

Tackle

So since we are all just spewing garbage and you've done everything right, your truck is possessed.

I give up because your truck has a one of a kind problem we've never seen.

Really...you have prety much all possible causes in this thread.

SouthernSteel

^Amen! There could be a number of different causes. Next time the MIL comes on, get the codes read. Sayin its coils is like saddling a dead horse if you don't know for sure.

biglee88

WhAt about the coil boots? Did u replace them? Any of them look like crap? It's just rubber over 14 years it can rot, tear, shrink ,the ridge on top that helps seal the spark plug hole can deteriorate from 14 years of service. If I was you and because boots are cheap I'd pull the coils and replace the boots before re installation I would blow all spark plug holes out with compressed air then reinstall. It sounds like water seeps down in your spark plug hole and untill it evaporates out from the heat of the engine it misses. But a miss fire is not good for your engine that's y they set check engine lights. You can damage your cats you can cause abnormal wear on your crank bearings from the abnormal pulsing. Just food for thought.