Miss fires?
 

I have a 2012 ecoboost I purchased private party. I have replaced the plugs, however I get what I think are misfires at aroud 2500 rpms under hard acceleration. It only happens under hard acceleration. The truck hesitates and occassionally the CEL will blink but not stay lit or throw a code. Run premium gas, and can't figure this out!

What brand of plugs and what were they gapped?

Motorcraft plugs that were supposedly pregapped. Gonna pull them and check the gap.
Have a livewire tuner, with no tune just configured for larger tires and cat back exhaust, everything else is stock. The CEL flashes occasionally when this happens, but never stays lit and never goes into limp mode. So no codes...yet

Have a look at the history of the 3.5 Ecoboost. Engine misfire issues are very common, but can easily be overcome. The ecoboost suffers from condensate that builds in the intercooler. On hard acceleration, condensate that pooled in the intercooler while driving gets blown through and blows out spark. Things to know:
1. Drill the 1/16” weep hole in the intercooler and the cooler will clean itself out while driving. The masses have done this with 100% success.
2. Once you have number one, put new motorcraft sp534 plugs in gapped .030. You will need to verify gap. Reminder, plugs need changed every 20k-30k miles to stay safe.

That is your ecoboost 101 to get the truck down the road. NOW, if the misfire issue has been present all along and not addressed, be prepared for needing new cats ando2 sensors.

Next, be on the lookout for cold start rattling. This would be your cam phasers failing. You can’t let that go... $4k job to fix, but the fix is just new parts. The root cause is clogged oil paths to the cam phasers. That actually can’t be fixed ver well!

I had this same problem. Replaced stock plugs with a step colder plus SP542 and gapped them at .025 since I'm tuned. Haven' had a problem since. If you are stock. Gap them at .030..NEVER trust regapped plugs. Always check them.

Took it to the stealership and they said it needs a new driver side turbo. Found some other posts and others have same issue. Plugs are fine. Its the wastegate opening prematurely. Also replaced the wastegate actuator and it did not fix the problem. Looks like its going to be a new turbo.