I purchase a 2012 F150 ECB last week with 84K miles. It ran fine for me on the test drive. So the wife and I bought it. The next day I was taking my second set of keys to the dealer for the Jeep JK I traded in and my truck began shuddering severely as we were driving up a steep local hill at ~ 50 - 55 MPH and a flashing Check Engine Light. The ECL never set for some reason. But driving it around I noticed the shuddering was occurring fairly frequently so I knew I had a problem.
I searched Google for answers after doing some drivability tests that set a cylinder #3 misfire (I pulled the code with my trusty ODBII scanner). For some reason this did not set the CEL on.
My first hint was a very good YouTube video that showed OEM Motorcraft plugs that had excessive gaps and cracks with Carbon tracking with far less than the Ford-stated 100K miles. I bought new plugs and when I pulled mine out sure enough...I had Motorcraft plugs with large electrode gaps and one plug also had two vertical cracks with obvious carbon tracking. I replaced all of the plugs and my truck now runs great!
Then of course...while doing further research after I replaced the plugs,
I found the 300+ pages on this very problem right here on this forum. I signed up and I am now a member of this forum.
I have been driving my truck every day since replacing the plugs and it runs awesome.