Please bear with me I have a 2011 super crew 3.5 L eco-boost it has recently started to stumble or shutter under full throttle runs great otherwise, and gets good gas mileage. Last year I changed all the coils and spark plugs. I turn the truck off filled up with gas started it back up and that is when the problem began. I thought I got some bad fuel so I ran the tank empty filled up with 89 and added some fuel injection cleaner. The problem is still there, I am running an SCT4 87tune. It only happens when I’m around 55 to 60 miles an hour and put my foot to the floor runs fine at an idle. I can put it in park and rev the engine with no problems. I was getting a bad clunk in between first and second gear when going slow around corners, I took the driveshaft out. I see no issues. I greased it with the special grease from Ford and that did not cure the clunking problem coming from the rear end. Can this be a transmission issue? Any help would be great. Thanks for reading this long post.

 

Coils could fail. Monitor Mode 6/Misfire counters data using a tool like Forscan. Misfires could happen below the threshold to set the CEL.

If the trans fluid is pushing 80-100K, could be that too.

 

Vehicle Information Miles?
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Clean the MAP sensors. The EcoBoost has 3 MAP sensors ....

 

Hey Jeff,

Did you use factory coils and plugs? Where did you get them from? I had the exact same issue as you and was certain it was the plugs. Changed them out and while the engine ran noticeably smoother, the truck still shuttered and bucked. After some research, I figured out that it was the torque convertor going bad. I purchased the following from amazon and poured it into the transmission and it fixed my problems right away, surprisingly.

 

That is a good product for sure but if it works, it is time to change your fluid. I also believe in Lubegard Red.