I have a 2011 f150 EcoBoost and the other day I decided to change the plugs. Everything went smoothly and the truck seemed much more responsive and gained a couple MPG, that was only for around 10 miles. Then under heavy load the truck had two misfires in cylinders 3 and 4 and also threw a code for “random misfire”. I have now been chasing these misfires all day with no luck. Nothing I have read on other posts have helped. I checked plug gal numerous times replaced all the boots, drilled the weep hole in the CAC and swapped ignition coils with no luck. All of the wiring appears to be in good condition there’s no carbon tracing on the old plugs or the new ones so I am close to giving up and just reaching out for help.

 

You might need to change the plugs. They should be replaced every 30-40k on those engines.

 

As stated in the original post i did not run into any issues until after i had changed the plugs.

 

Try putting the old plugs back in and see what happens.

 

x2

glc might be on to something.

 

What was the solution to your mis-fire issue?