I have been the proud owner of a 99 f 150 , 5.4 4x4 since it had 13 miles on it that has NEVER been to the dealer...seems I am one of the few and the proud..anyway I am almost a daily reader and a very rare poster... but I need some help...On my way to work yesterday Am ...after about a 5 min warm up and less than a mile to the interstate I was off to start my day a mile up the highway at about 70 mph it was missin bad....not coil pack or dead cylinder missing but missin none the less...CEL blinked 15 times and stopped for exactly one min then did it again ...i counted 14 the first time and 15 the second cuz i was lookin for it...on the way home still ran terrible but no light ...went to auto zone to get codes read...no codes......this morning same deal ...warm up , highway about 70, light blinks 15 times, i was waitin'...still missin.....way home same deal but no light....after the auto zone episode, i went home and cleaned throttle body thouroughly , cleaned K&N, and went for a ride same deal....fellas. i have 109k on this truck , but...I have had it for 6 years and it has been driven hard no doubt, pulled EVERTHING I ever hooked to including pulling my neighbors 56' Nortech that weighs 21,000lbs sitting on a trailer out of the water[ thank god for 4 lo] I am trying to save a trip to the dealer . Any help would be much appreciated...PS...NO MODS....K&N , 3" body . 33's 3.73....otherwise stock....

 

I don't know how much this will help but I would clean the mass airflow sensor as well. With a K&N or similar air filter it will get some oil film built up on it over time.

As for what I "think" the problem is... a bad plug or coil over the plug.

Just out of curiosity, when was the fuel filter changed last?

 

I have had this problem, happened at about 70,000 miles and at about 60 to 70 miles an hour. Usually only under load. I changed the plugs and wires. About 6 months after that it started again. I narrowed it down to the wires. on the passenger side they sit funny and overlap. for what ever reason they were arcing each other. When it was at an idle it wouldn't do it so didn't think it was a problem with a dead hole. I spent less than $10.00 on some wire seperaters and never had the problem again. I now have 114,000 miles on the truck and runs like a champ. Hope this helps!!!!

 

Fuel filter was changed around 75k , thanks for your responses .