so i wanted to start off by saying hello and to thank you all for how much this site has helped me but after alot of reading this is my first post I have just recently bought another f150 is a 99 5.4l 4x4 it has 140000 miles the truck sat before i bought it for at least a year and before that about 6 years inside a garage there is absolutely no rust on this truck at all so I bought it first thing i did was new manifolds and studs as they were leaking terribly next was front brakes and calipers and spark plugs bc i had a miss and i threw a p0303 and p0308 code so i put a new cop on #3 plug it helped but still had random misfire so thats when i changed all the plugs number 3 plug was super rusty and number 8 had about an inch of hard crusty white residue but was all dry ... as i got it to break away slowly i would blow air down the hole to get the crap out and the 1 time i blew in the hole i got some of the dust in my mouth ... tasted like antifreeze so i really started looking around but i cannot find any leaks so finish changing all the plugs 2 days ago and she ran awesome until this morning last night we had very strong winds and heavy rain and i got in the truck this morning drove about 2 miles ran fine went into bank came out fired it up and misfire from hell and now it is during and idle and while under load ... i used motorcraft plugs by the way and all the cops had good looking boots but i did forget to use dielectric grease oops so my question is could this be rain related and leaking into cylinder 8 or 3 and thats y they were rusty and corroded or do i need to start saving my money to buy new cops ... i am in the first months of opening my own motorcycle repair shop so i am always pulling trailers and such so i need to get this fixed asap and i appologize if all this has been asked before i tried to search the best i could..
Thanks
Alex

 

Oh man, I think you just set the record for the longest sentence ever on the the FTE web site! Yer killin' us older folks!

What condition is the hood seal at the rear of the hood? If it's shot, rainwater can be dripping in on the engine.

 

Alex, since your going to depend on the truck for your repair shop, invest in a good scanner and learn how to use it for viewing live data and seeing when the data is out of limits.
For example use it to look at mode 6, test 53.
This shows the misfire counts for each cylinder.
It will show you what ones need correction whether the coil is new, the boot is bad etc.
You need to get into doing the service correctly to minimize the wasting of your time by failing to fix the issues reliably and quickly.
Go back and pull those cylinders coils, inspect the boots for being hard, pin holes and use the proper grease to help seal the boots to the plug tips.
Grease needs to be used to help the boot tip find the plug tip so it does not hang up to the side and cause misfires.
Check out the heater hoses for leakage.
Make sure the coils and boots set down on the cylinder head plug well to help keep water out.
Check the hood seal as suggested.
Bottom line is you have 8 coils not 1 or 2.
If 1 or more are not working the motor misses so it's 8 times more sensitive than the old ignitions.
Sorry if it sounds like a lecture but you need to look at these things a bit differently for your own success.
Good luck.