I've got a 2003 5.4 that has 70,000 miles on it. It runs like new and always has, I take very good care of this truck inside and out. I decided to spray the motor off last Thursday with my garden hose. Well now I've got a misfire on cylinder 8 according to the scan I ran on it with an autotap program. It's definitly misfiring as you can feel it. I've left the hood open for everything to dry for 3-4 days and still no go. I know my way around a tool box and have worked on many ATV motors but this is no the same. I'm not even sure how to remove the coils form the plugs and I'm not sure which cylinder is #8. I've always changed plugs and wires on all my vehicles but that was years ago before they got all fancy. Help and thanks in advance.

 

There is a 7mm screw that holds the COP in place on top of the spark plug. Number 8 cylinder is the back one on the driver side of the truck.
Pull the COP off, and use a compressed air nozzle to blow out the spark plug well. Pull the plug and check for a broken or cracked insulator on it. If it is good, put it back in, and check the COP for arcing tracks on the boot. You can get a new boot if it needs it. Be sure to put some di-electric grease inside the boot where it fits over the plug. Good luck!

 

also check the engine calbel going from the ecu could of got some water in there i think its a 10 mm bolt just to make sure its the on right in fron of the ac low presser port

 

Sounds like there might be moisture inside the top of the
Distributor cap.

Also, could be the engine was to warm & you cracked a spark plug.

I used to detali cars & i would cover with a plastic bag,
foil or something similar, when i pressure wahed it down.
Still happened every now & then.

98 5.4 85 unkillable 300
74 Mean as the Steeler defense: Mercury capri built with Ford guts

 

I have resolved the problem. Water got down in the spark plug hole. I had to remove the COP and then use an aire compressor to blow the water out of the hole. Put some dielectrical grease on the plug boot and bolted everything back together.

Words of advice, do not spray down the engine unless you have too, or if you are getting ready to change the plugs.

 

You should take a look under the hood of your truck. There is no distributor cap and the spark plugs are six inches down inside a well. Water can get down in the well and is exactly what he found.