I’m posting this thread to share my recent experience and hopefully save some people headache and money. This thread will be long.
2004 F150 XLT 5.4 3v with 201000. At 194k I did a complete timing repair with all lash adjusters and cam followers. Did all the plugs with new coil packs. VCT solenoids and sensors as well as other miscellaneous parts and maintenance. Total in parts $2600. I did all the labor.
Three weeks ago and 7000k later my truck misfired twice and died while driving. Had it towed to garage. After $400 for “diagnosis” they said I needed new coil packs, 6 of 8 were bad. $1,100 estimate to do the job. I said thanks but no thanks I can do it myself. Drove the truck home and after 6 miles same thing happened, misfired and died. Had it towed to my house. Codes show problems with coil packs. P0351 and P0356. I purchased new Motocraft coil packs and replaced the aftermarket ones I put in during the overhaul. Test drives still did the misfiring and shutting off. Coil packs 1 and 6 were the culprit. Swapped 1 and 2 and 5 and 6 and same problem and codes. Replaced plugs for 1 and 6. Same problem but the truck stopped throwing any codes.
Searched the internet and found an old thread with the owner having same issues. After he had spent money chasing problems he changed his crank position sensor and his problems were solved.
So, I purchased new Motocraft crank position sensor, replaced the recently replaced Duralast sensor, and the truck is running fine. The duralast sensor had some dirt on the end, not sure from the engine or when I removed it (tight in there and could have picked up some grime on removal)! No further misfires and no dying when driving.
I understand that a bad crank position sensor has its own codes but after looking at all the symptoms I was having the crank position sensor made sense. After the truck would die out, the truck would crank over but not start. After 30 minutes or so the truck would fire up again, run fine then misfire and quit. Also, with no issues for 7000k miles, I honestly doubt 6 of 8 coil packs would suddenly crap out. Even cheap ones.
What I know is these engines run great if taken care of and not many mechanics know how to work on them. I’m a YouTube mechanic, so by no means I’m an expert. But I know people can go down a rabbit hole with these engines if they listen to every mechanic. I would have paid $1,100 for nothing. Then probably $1400 for fuel pump and so on and so on.
Anyway, this may help someone in the future. I hope it does. Think over the symptoms your having before throwing money at a diagnosis that may very well not be accurate.
Sorry for the long thread and thanks for reading.

 

Fighting same thing with my 95, mechanics no longer around, they are parts changers, hell I can do that, without testing anything, the dealership wants $95/hr to check/work, now I understand they have to 'make a living', that's above and beyond 'make a living' and when it doesn't fix it...O, they were bad, OK, give me, my old parts(deer in head light stare) we threw away. I can change parts too, just cant afford to start down that rabbit hole, of stupidity. Then the mom/pop place tells me speedo was like that, (changed MLPS no reverse lights) speedo reads 70-80 mph, drive/reverse, at idle.