I have a 2000 F150 5.4. A couple of weeks ago I changed out all 8 spark plugs as it had not been done yet (119000 miles on the truck). I bought new boots to put in also but took them back because the existing ones were in very good shape. This solved the spitting/sputtering feeling that I was getting when accelerating (and cleared the SES light). Until about 2 days ago. The scanner that the auto parts store guy used said that I had a cylinder 5 misfire (same as before) and the spitting/sputtering is worse when I accelerate and when idling (SES is back and sometimes flashes).

Here's my question: bad coil cap, bad fuel injecter, or possibly something else?

Any help would be greatly appreciated
Thank You

 

Hi and welcome to the forum

The most common cause of a misfire is a bad spark plugs, but since you've replaced them and have the same symptom as before, the next likely cause is a bad COP (Coil On Plug).
You can swap #5 COP with another one (#1 is easy to access), and then clear the code by removing a battery terminal for 5 minutes. Drive the truck until the check engine light comes on again and then get it scanned to see what set the code. If the misfire code follows the COP then you know you've found the problem.
Or you can save a bunch of time but spend some money and have your dealer do a cylinder power balance after moving the COP to see if the misfire followed the COP.