Im Not sure how to post on here.This being my first time.
I purchased a 2006 F150 XLT with 5.4 and about 144k
Well the day i was going to pick it up from the dealer(MUELLER FAMILY AUTO) they called me and said when they were pulling it in to get it ready for me they noticed it started kinda hard so they were gonna change fuel pump. Ok thanks i said. Well it was real cold here in Wisconsin & It was ok the day before when i test drove it.
So heres where the fun starts
It had a random misfire which occured while driving it home on freeway(70mph) right after buying it. Next day I stopped after work at autozone and advance to have it scanned and determined cylinder 4 misfire and codes were recently cleared?!
So i took it back, they agreed to fix it, they changed 3 spark plugs(idk what kind?) Well a week later random misfire came back. was only happening at higher speeds. Went back again and they changed the plug again. Misfire was always on cylinder 4. Well random misfire came again. I then changed coil pack and injector on cylinder 4. Ran good and nice smooth low idle like it should be.
Random misfire came back on same cylinder. I then took it to a local Ford dealer where they also changed that plug cause it wasnt a Motorcraft. Well random misfires returned on same cylinder. I then moved around coil packs and put a known good one on cylinder 4, 8 & 5. It ran good for a cple days with no misfires but chugging started which got worse and dieseling sound. I then found a bad coil connector. I changed that and ALL coil packs with new ones. For 4 days No More misfire but it chugged a bit and dieseling reduced. Chuggin got worse and worse then engine light returns now misfire on cyl 8. This whole time the 5.4 tick was there and seemed to get worse. So i then put one of my old cps on cyl 8. Now the tick is really less noticeable but the chug exists and you can actually here a sputter from exhaust.
Plugs werent changed during or after MY own repairs. The current plugs are most likely different brands and i hear these engines are finnicky.(NEED all the same kind/brand of plugs (MOTORCRAFT)) I did use fuel system cleaners and premium gas.
So now i really have no idea what next. Both places couldnt diagnose it which was a total of at least 3 technicians.
Could it be the Cat convertor? Plugs? Fuel filter? or what else? what to try and diagnose next? Please help
Thanx

 

I've moved this post to engine section so you can get appropriate assistance.


Have they replaced the FPDM?

 

Yes changed the fpdm and still didnt change anything. Took it in for all new plugs after numerous misfires on cylinder 8. Now its runs great and the tick is even gone!
Thanx