Truck was running poorly So I did entire timing chain, cam phasers, tensioners, solenoids for cam phasers. Truck immediately was stronger, but still intermitantly was misfiring. Found bad plug connections on two cylinders, #7 and #3. Replaced plugs on top of Coil Packs on those two cylinders. When I was doing the timing set, I remember one of the rockers was loose on cylinder three(intake rocker) but thought it might pump up. Unfortunately it was ticking after I put everything back together. Then a week later the engine make a weird noise, and the lifter was quiet. Fast forward, then when the engine was cold, it would run rough and throw a P0303 code. I changed the coil pack, spark plug, and injector on cylinder 3. Seem to run great, but on a trip to Ohio,Last week at around 4700 rpm while climbing a mountain, it threw a P0303 again and ran rough. Cleared code and continued journey. On the way back from Ohio started the engine while cold and the code came up again. Once the engine is warm it is smooth. Could I be looking at a bad lifter on cylinder 3 that would cause a misfire? I feel real dumb for not replaced the lifters when I had the cams out. By the way this is a 5.4 3valve (2005 F150) with 140k miles. I am running full synthetic 5-30 per Fordmakuloco recommendations. I also have the high volume OIl pump installed. All of this was done with last 6k miles. Whats yours thoughts for a solution. Could the valves be floating at high rpm, Or am I looking at bad lifters. Very frustrating as I just spent a great deal of time, and used all Ford parts except oil pump. I had diagnostics ran it it showed normal specs on injectors, spark, etc. Help? That cylinder three is just giving me a fit.

 

Probably do a compression test and a leak down test to see where you are at..

 

You need to watch this video. He says the failure is most common on cyl 3.

 

Thank you I missed that video from him....Used his video for my timing set replacement. Oh Lord scared to pull that valve cover. But I will.....